Control device for internal combustion engines

Abstract

This minimizes the decrease in the accuracy of PM (particulate matter) accumulation calculations. [Solution] The internal combustion engine 10 includes a GPF 18 provided in the exhaust passage 15 to collect particulate matter in the exhaust, and a pressure sensor 50 that detects pressure information including the pressure upstream of the GPF 18 from the exhaust. The control device 100 performs an estimation process to calculate an estimated amount of particulate matter deposited in the GPF 18 based on the operating state of the internal combustion engine 10, a range calculation process to calculate upper and lower limits that define the range of the amount of particulate matter deposited in the GPF 18 based on the pressure information, and a correction process to correct the estimated amount of deposit so that it falls within the range defined by the upper and lower limits if the estimated amount of deposit is outside the range defined by the upper and lower limits.

Description

Technical Field

[0001] The present invention relates to a control device for an internal combustion engine.

Background Art

[0002] The internal combustion engine described in Patent Document 1 includes a filter that collects particulate matter in exhaust gas and a pressure sensor that detects the differential pressure before and after the filter in an exhaust passage. Then, a first estimated amount is calculated as an estimated amount of particulate matter deposited on the filter based on the operating state of the internal combustion engine. Also, a second estimated amount is calculated as an estimated amount of particulate matter deposited on the filter based on the differential pressure before and after the filter. And, the larger value of the first estimated amount and the second estimated amount is calculated as the deposition amount of particulate matter.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, even if the differential pressure before and after the filter is the same, the actual deposition amount on the filter may be different. Therefore, if the second estimated amount calculated based on the differential pressure before and after the filter is directly used as the deposition amount of particulate matter, the calculation accuracy of the deposition amount may decrease.

Means for Solving the Problems

[0005] A control device for an internal combustion engine that solves the above problems is applied to an internal combustion engine that includes a filter provided in the exhaust passage for collecting particulate matter in the exhaust, and a pressure sensor for detecting pressure information including the pressure upstream of the exhaust from the filter. This control device performs the following: an estimation process for calculating an estimated amount of particulate matter deposited on the filter based on the operating state of the internal combustion engine; a range calculation process for calculating upper and lower limits that define the range of the amount of particulate matter deposited on the filter based on the pressure information; and a correction process for correcting the estimated amount of deposit so that it falls within the range defined by the upper and lower limits if the estimated amount of deposit is outside that range. [Effects of the Invention]

[0006] According to this invention, it is possible to suppress a decrease in the accuracy of calculating the amount of particulate matter deposited. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic diagram of an internal combustion engine to which one embodiment of the control device is applied. [Figure 2] Figure 2 is a flowchart showing the procedure for calculating the estimated sediment amount performed by the control device of the same embodiment. [Figure 3] Figure 3 is a graph showing the relationship between the upper and lower limits of the accumulation amount and the exhaust pressure. [Figure 4] Figure 4 is a timing chart illustrating the operation of the embodiment. [Modes for carrying out the invention]

[0008] Below, one embodiment of a control device for an internal combustion engine will be described with reference to Figures 1 to 4. <Configuration of an internal combustion engine> As shown in Figure 1, the internal combustion engine 10 has multiple cylinders 10a, and an intake passage 13 is connected to the intake port of each cylinder 10a. A throttle valve 14 is provided in the intake passage 13 to adjust the amount of intake air.

[0009] Each cylinder 10a has a combustion chamber equipped with a fuel injection valve 11. In the combustion chamber of each cylinder 10a, a mixture of air drawn in through the intake passage 13 and fuel injected from the fuel injection valve 11 is ignited by a spark discharge and combusted. The exhaust gas produced by the combustion of the mixture in the combustion chamber is discharged into an exhaust passage 15 connected to the exhaust port of the internal combustion engine 10.

[0010] A three-way catalyst 17 is provided in the exhaust passage 15. This three-way catalyst 17 oxidizes hydrocarbons (HC) and carbon monoxide (CO) contained in the exhaust to produce water and carbon dioxide. In addition, the three-way catalyst 17 reduces nitrogen oxides (NOx) contained in the exhaust to produce nitrogen.

[0011] A gasoline particulate filter (GPF) 18 is provided in the exhaust passage 15 downstream of the three-way catalytic converter 17. The GPF 18 is a filter that collects particulate matter (hereinafter referred to as PM) in the exhaust gas, with the three-way catalytic converter supported on top.

[0012] The control device 100 is equipped with a CPU 110, memory 120, etc., and the CPU 110 executes programs stored in the memory 120 to perform various controls on the internal combustion engine 10.

[0013] The control device 100 receives detection signals from various sensors. For example, a pressure sensor 50 is provided in the exhaust passage 15, downstream of the three-way catalytic converter 17 and upstream of the GPF 18. This pressure sensor 50 detects pressure information, including the pressure upstream of the GPF 18. This pressure information is the differential pressure ΔP between the exhaust pressure EP upstream of the GPF 18 and atmospheric pressure. A crank angle sensor 53 is provided near the crankshaft of the internal combustion engine 10, and the engine speed NE of the internal combustion engine 10 is calculated based on the detection signal from this crank angle sensor 53. The internal combustion engine 10 is also equipped with an air flow meter 54 for detecting the intake air volume GA and a water temperature sensor 55 for detecting the coolant temperature THW of the internal combustion engine 10.

[0014] The control device 100 controls the fuel injection of the fuel injector 11 and the opening degree of the throttle valve 14. Furthermore, the control device 100 calculates the PM accumulation amount Ps, which is the amount of PM that accumulates sequentially in the GPF18 during engine operation and then gradually decreases from the GPF18 during the regeneration process described later. The calculation of this PM accumulation amount Ps will be described later.

[0015] When the amount of PM deposited Ps exceeds a predetermined regeneration threshold α, the control device 100 performs a regeneration process for the GPF18 in order to burn off the PM deposited on the GPF18 and regenerate the GPF18. This regeneration process is a well-known process, so a detailed explanation will be omitted, but basically it involves increasing the temperature of the GPF18 and changing the atmosphere of the GPF18 to an oxidizing atmosphere to burn off the PM.

[0016] Figure 2 shows the procedure for calculating PM accumulation amount Ps performed by the control device 100. The series of processes shown in Figure 2 are realized by the CPU 110 executing a program stored in the control device 100's memory 120 at predetermined calculation cycles T. Furthermore, in the following, step numbers are represented by numbers preceded by "S".

[0017] In the series of processes shown in FIG. 2, the control device 100 first acquires the engine rotational speed NE, the filling efficiency η, and the coolant water temperature THW (S100). The filling efficiency η is calculated by the control device 100 based on the engine rotational speed NE and the intake air amount GA.

[0018] Next, the control device 100 calculates an update amount ΔPs of the PM deposition amount Ps based on the engine rotational speed NE, the filling efficiency η, and the coolant water temperature THW (S110). The PM deposition amount Ps is the amount of PM captured by the GPF 18 and is an estimated deposition amount of PM calculated based on the operating state of the internal combustion engine 10.

[0019] Specifically, the control device 100 calculates a PM emission amount PA, which is the amount of PM discharged from the internal combustion engine 10 to the exhaust passage 15 per calculation cycle T, based on the engine rotational speed NE, the filling efficiency η, and the coolant water temperature THW. Further, the control device 100 calculates the temperature of the GPF 18 based on the engine rotational speed NE and the filling efficiency η. Further, the control device 100 calculates a PM combustion amount PB, which is the amount of PM burned by the GPF 18 per calculation cycle T, based on the temperature of the GPF 18 and the like. Then, the control device 100 substitutes the value obtained by subtracting the PM combustion amount PB from the PM emission amount PA into the update amount ΔPs. Therefore, when the PM emission amount PA is greater than the PM combustion amount PB, the update amount ΔPs becomes a positive value, and when the PM combustion amount PB is greater than the PM emission amount PA, the update amount ΔPs becomes a negative value.

[0020] Next, the control device 100 updates the PM deposition amount Ps by adding the update amount ΔPs to the currently calculated PM deposition amount Psp (S120). Therefore, when the PM emission amount PA is greater than the PM combustion amount PB, the PM deposition amount Ps increases, and when the PM combustion amount PB is greater than the PM emission amount PA, the PM deposition amount Ps decreases. Each of the processes S100, S110, and S120 constitutes an estimation process for calculating an estimated deposition amount of particulate matter deposited on the filter based on the operating state of the internal combustion engine 10.

[0021] Next, the control device 100 acquires the current differential pressure ΔP (S130). Next, the control device 100 executes a range calculation process for calculating the upper limit value Psmax and the lower limit value Psmin based on the acquired differential pressure ΔP (S140).

[0022] As shown in FIG. 3, when the value of the differential pressure ΔP, which is pressure information, is a certain value ΔP1, it has been found that the actual PM deposition amount varies depending on the PM deposition method in the GPF18, and the PM deposition amount becomes a value within the range PsR defined by the upper limit value Psmax and the lower limit value Psmin. Here, the PM deposition method refers to a state where PM is deposited almost uniformly in the GPF18, a state where the PM deposition amount is larger on the rear end side of the GPF18 than on the front end side, and the like. And as the differential pressure ΔP increases, both the upper limit value Psmax and the lower limit value Psmin tend to increase.

[0023] Therefore, in the present embodiment, through preliminary tests and the like, the range PsR of values that can be taken as the actual PM deposition amount is obtained for each differential pressure ΔP. And a setting map showing the correspondence between the upper limit value Psmax and the lower limit value Psmin defining the range PsR and the differential pressure ΔP is stored in the memory 120. In the process of S140, the control device 100 refers to the setting map and calculates the upper limit value Psmax and the lower limit value Psmin based on the differential pressure ΔP. Instead of the setting map, the correspondence between the upper limit value Psmax and the lower limit value Psmin and the differential pressure ΔP may be expressed by a model formula.

[0024] Next, the control device 100 determines whether the current operating state of the internal combustion engine 10 is stable (S150). Here, the operating state being stable means a state where the variation of the differential pressure ΔP is suppressed. In the process of S150, the control device 100 determines that the operating state of the internal combustion engine 10 is stable when the operating state of the internal combustion engine 10 is in a steady state or in an idle operating state.

[0025] In the process of S150, if it is determined that the operating state of the internal combustion engine 10 is stable (S150:YES), the control device 100 determines whether the PM accumulation amount Ps updated in the process of S120 is greater than or equal to the upper limit value Psmax (S160). If it is determined that the PM accumulation amount Ps is greater than or equal to the upper limit value Psmax (S160:YES), the control device 100 performs a process to guard the PM accumulation amount Ps with the upper limit value Psmax by substituting the upper limit value Psmax into the PM accumulation amount Ps (180).

[0026] On the other hand, if the S160 process determines that the PM accumulation amount Ps is less than the upper limit Psmax (S160: NO), the control device 100 executes the S170 process. In the S170 process, the control device 100 determines whether the PM accumulation amount Ps updated in the S120 process is less than or equal to the lower limit Psmin. If it is determined that the PM accumulation amount Ps is less than or equal to the lower limit Psmin (S170: YES), the control device 100 substitutes the lower limit Psmin into the PM accumulation amount Ps, thereby executing a process to lower the PM accumulation amount Ps to the lower limit Psmin (S190).

[0027] The processes S160, S170, S180, and S190 each consist of a correction process that adjusts the estimated amount of particulate matter to a value within the range defined by the upper and lower limits, if the estimated amount of particulate matter is outside the range defined by the upper and lower limits.

[0028] Then, if the process in S180 is completed, or if the process in S190 is completed, or if a negative result is obtained in the process in S150, or if a negative result is obtained in the process in S170, the control device 100 terminates the execution of this process in the current calculation cycle T.

[0029] <Operation of this embodiment> As shown in Figure 4, when the actual amount of PM deposited increases or decreases, the differential pressure ΔP also increases or decreases. Therefore, the upper limit Psmax and the lower limit Psmin change in accordance with the increase or decrease in the actual amount of PM deposited.

[0030] Then, if the PM accumulation amount Ps calculated in the process of S120 above is greater than or equal to the upper limit Psmax (distance traveled t1 to t2), the upper limit Psmax is substituted into the PM accumulation amount Ps and an upper limit guard is performed.

[0031] On the other hand, if the PM accumulation amount Ps calculated in the process of S120 above is less than or equal to the lower limit Psmin (distance traveled t3 to t4), the lower limit Psmin is substituted into the PM accumulation amount Ps and a lower limit guard is performed.

[0032] <Effects of this embodiment> (1) If there is a significant discrepancy between the operating conditions used when conducting the conformity test to calculate the PM accumulation amount Ps and the operating conditions used when calculating the PM accumulation amount Ps during the operation of the internal combustion engine 10, the calculated PM accumulation amount Ps may deviate excessively from the actual PM accumulation amount.

[0033] Furthermore, because the calculation accuracy of PM accumulation Ps is shifted to the positive side and to the negative side in operating regions, repeated operation in the positive-side shifting region may result in an excessively high PM accumulation Ps. Conversely, repeated operation in the negative-side shifting region may result in an excessively low PM accumulation Ps.

[0034] In this respect, according to this embodiment, the upper limit Psmax and lower limit Psmin that define the range PsR of PM accumulation amount on the GPF18 are calculated based on the differential pressure ΔP, which is pressure information including the pressure upstream of the exhaust gas from the GPF18. If the PM accumulation amount Ps calculated based on the operating state of the internal combustion engine 10 is outside the range PsR defined by the upper limit Psmax and lower limit Psmin, a correction process is performed to correct the PM accumulation amount Ps so that it falls within the range PsR. Therefore, a decrease in the calculation accuracy of the PM accumulation amount Ps can be suppressed.

[0035] (2) The above correction process includes a process to set an upper limit guard on the PM accumulation amount Ps with an upper limit value Psmax, and a process to set a lower limit guard on the PM accumulation amount Ps with a lower limit value Psmin. Therefore, it is possible to prevent the PM accumulation amount Ps from becoming excessively large beyond the upper limit Psmax, and to prevent the PM accumulation amount Ps from becoming excessively small beyond the lower limit Psmin.

[0036] (3) When the operating state of the internal combustion engine 10 is unstable, the differential pressure ΔP in the above pressure information becomes unstable, which may worsen the calculation accuracy of the upper limit Psmax and the lower limit Psmin. In this embodiment, however, the above correction process is executed when a positive determination is made in the S150 process shown in Figure 2, that is, when the operating state of the internal combustion engine 10 is stable. Therefore, the PM accumulation amount Ps can be corrected when the calculation accuracy of the upper limit Psmax and the lower limit Psmin is ensured.

[0037] (4) When the PM accumulation amount Ps exceeds the predetermined regeneration threshold α, the regeneration process of GPF18 is started. In this embodiment, as described above, the decrease in the accuracy of calculating the PM accumulation amount Ps can be suppressed. Therefore, it is possible to prevent the GPF18 regeneration process, which is determined based on the PM accumulation amount Ps, from being started incorrectly.

[0038] <Example of changes> This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0039] In the process of S150 shown in Figure 2, the control device 100 may determine that the operating state of the internal combustion engine 10 is stable when the absolute value of the longitudinal acceleration of the vehicle equipped with the internal combustion engine 10 is less than or equal to a predetermined value and the vehicle is in a state of gentle acceleration or gentle deceleration.

[0040] The process in S150 shown in Figure 2 may be omitted, and the process in S140 may be executed first, followed by the process in S160. In this case as well, effects other than those described in (3) above can be obtained.

[0041] The above pressure information was the differential pressure ΔP between the exhaust pressure EP upstream of GPF18 and atmospheric pressure. Alternatively, the above pressure information may also be the differential pressure between the exhaust pressure EP upstream of GPF18 and the exhaust pressure downstream of GPF18.

[0042] The amount of PM accumulation Ps to be updated ΔPs may be calculated in a manner different from that of the above embodiment. The placement of the GPF18 is not limited to the downstream of the three-way catalyst 17 in the exhaust passage 15. Furthermore, the GPF18 may be a filter that does not support the three-way catalyst.

[0043] The control device 100 is not limited to one that includes a CPU and memory and performs software processing. For example, the control device 100 may include a dedicated hardware circuit, such as an ASIC, that performs hardware processing for at least a portion of what is processed by software in the above embodiment. That is, the control device 100 may include a processing circuit having any of the following configurations (a) to (c): (a) A processing circuit comprising one or more processing units that perform all of the above processing according to a program, and one or more program storage devices such as ROMs that store the program. (b) A processing circuit comprising one or more processing units and one or more program storage devices that perform a portion of the above processing according to a program, and one or more dedicated hardware circuits that perform the remaining processing. (c) A processing circuit comprising one or more dedicated hardware circuits that perform all of the above processing. The program storage device, i.e., computer-readable medium, includes any available medium that can be accessed by a general-purpose or dedicated computer. [Explanation of Symbols]

[0044] Internal combustion engine… 10a…Cylinder 11…Fuel injector 13…Intake passage 14…Throttle valve 15…Exhaust passage 17…Through catalytic converter 18…GPF 18…Gasoline particulate filter 50…Pressure sensor 53…Crank angle sensor 54…Air flow meter 55…Water temperature sensor 100…Control unit 110…CPU 120…Memory

Claims

1. A control device for an internal combustion engine, comprising a filter installed in the exhaust passage for collecting particulate matter in the exhaust, and a pressure sensor for detecting pressure information including the pressure upstream of the exhaust from the filter, The control device is An estimation process for calculating the estimated amount of particulate matter deposited on the filter based on the operating state of the internal combustion engine, A range calculation process that calculates upper and lower limits for defining the range of particulate matter accumulation on the filter based on the pressure information, If the estimated amount of sediment falls outside the range defined by the upper and lower limits, a correction process is performed to adjust the estimated amount of sediment so that it falls within that range. Control device for internal combustion engines.

2. The correction process includes a process to set an upper limit guard on the estimated deposit amount with the upper limit value, and a process to set a lower limit guard on the estimated deposit amount with the lower limit value. A control device for an internal combustion engine according to claim 1.

3. The correction process is performed when the operating state of the internal combustion engine is stable. A control device for an internal combustion engine according to claim 1.

4. If the estimated amount of sediment exceeds a predetermined threshold, the filter regeneration process will be initiated. A control device for an internal combustion engine according to claim 1.

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