JP7206625B2 - Control device for internal combustion engine - Google Patents

Description

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

In order to reduce the amount of NOx generated in an internal combustion engine, an EGR device is provided that takes part of the exhaust gas from the exhaust passage of the internal combustion engine as EGR (Exhaust Gas Recirculation) gas and recirculates the EGR gas to the intake passage of the internal combustion engine. It is known.

In Patent Document 1, the flow rate of EGR gas is calculated based on the pressure difference between the intake pressure and the exhaust pressure respectively detected by an intake pressure sensor and an exhaust pressure sensor, and the opening of the EGR valve that realizes the flow rate is calculated. ing.

JP-A-10-238412

However, with the conventional technology, when the amount of intake air is low, the increase in exhaust pressure (back pressure) cannot be accurately detected, and depending on the operating conditions, a large amount of EGR gas is supplied to the intake passage, which may cause deterioration of combustion. be. In addition, the supply of a large amount of high-temperature EGR gas may deteriorate the durability of intake system components.

Therefore, an object of the control device for an internal combustion engine disclosed in the present specification is to supply an appropriate amount of EGR gas even when the amount of intake air is small.

In order to solve this problem, the internal combustion engine control apparatus disclosed in this specification recirculates part of the exhaust gas from the exhaust passage of the internal combustion engine to the intake passage of the internal combustion engine as EGR (Exhaust Gas Recirculation) gas. a passage, an EGR valve provided on the EGR passage to adjust the flow rate of the EGR gas, a particulate filter provided on the exhaust passage to collect particulate matter in the exhaust gas, and the internal combustion engine. an intake air amount detection unit for detecting an intake air amount; an exhaust pressure detection unit for detecting pressure in the exhaust passage on the upstream side of the particulate filter as an exhaust pressure; a PM accumulation amount estimator for estimating an amount of PM accumulated; and an estimation of PM accumulated in the particulate filter after the intake air amount becomes less than the first threshold when the intake air amount is less than the first threshold. and an estimated amount of PM accumulated in the particulate filter before the intake air amount became less than the first threshold value . a determination unit, a second determination unit that determines a first target value of the flow rate of the EGR gas based on the exhaust pressure when the intake air amount is equal to or greater than a first threshold value, and a flow rate of the determined EGR gas a control unit that controls the degree of opening of the EGR valve according to a first target value .

According to the control device for an internal combustion engine disclosed in this specification, an appropriate amount of EGR gas can be supplied even when the amount of intake air is small.

FIG. 1 is a schematic diagram showing the configuration of an engine system to which a control device for an internal combustion engine according to one embodiment is applied. FIG. 2(A) is a diagram showing an example of a map for obtaining the PM deposition amount from the intake air amount and the exhaust pressure, and FIG. 2(B) is a diagram showing an example of a map for obtaining the EGR gas flow rate from the exhaust pressure. is. FIG. 3(A) is an enlarged view of the low GA region of the map shown in FIG. 2(A), and FIG. 3(B) is a view showing an example of the map used to determine the EGR gas flow rate. FIG. 4 is a flowchart showing an example of EGR gas flow rate calculation processing executed by the ECU. FIG. 5 is a diagram showing an example of a map for obtaining the EGR gas flow rate from the PM estimated deposition amount.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, etc. of each part may not be illustrated so as to completely match the actual ones. In some drawings, details may be omitted.

First, with reference to FIG. 1, an engine system to which a control device for an internal combustion engine according to one embodiment is applied will be described. FIG. 1 is a schematic diagram showing the configuration of an engine system 100 to which a control device for an internal combustion engine according to one embodiment is applied.

The engine system 100 includes an internal combustion engine 10 mounted on a vehicle. The internal combustion engine 10 of the present embodiment is assumed to be of the in-line four-cylinder type, but the present invention can be applied to internal combustion engines having any number of cylinders. Note that FIG. 1 shows a cross section of one of the four cylinders. A piston 12 is provided in each cylinder of the internal combustion engine 10 . An intake passage 20 and an exhaust passage 30 communicate with each cylinder.

The intake passage 20 is provided with an air flow meter 21 for detecting the amount of intake air, an electronically controlled throttle valve 22 and a surge tank 23 in this order from the upstream side. The airflow meter 21 is an example of an intake air amount detector.

An exhaust purification catalyst 31 that purifies exhaust gas is arranged in the exhaust passage 30 . An exhaust pressure sensor 32 that detects the pressure in the exhaust passage 30 on the upstream side of the exhaust purification catalyst 31 is arranged in the exhaust passage 30 . The exhaust purification catalyst 31 is an example of a particulate filter, and the exhaust pressure sensor 32 is an example of an exhaust pressure detector.

Each cylinder of the internal combustion engine 10 is provided with a fuel injector 15 for injecting fuel into an intake port, a spark plug 16 for igniting the air-fuel mixture in the combustion chamber, an intake valve 17, and an exhaust valve 18. there is Note that in the present invention, an in-cylinder injector that directly injects fuel into the cylinder may be provided in place of the fuel injector 15 or together with the fuel injector 15 .

A crank angle sensor 19 for detecting the rotation angle (crank angle) of the crankshaft 11 is provided near the crankshaft 11 of the internal combustion engine 10 . A water temperature sensor 52 for detecting the temperature of the cooling water of the internal combustion engine 10 is also provided. An accelerator position sensor 44 that detects the position of the accelerator pedal is installed near the accelerator pedal.

The internal combustion engine 10 also includes an EGR passage 40 for performing so-called external EGR (Exhaust Gas Recirculation), in which the exhaust gas in the exhaust passage 30 is recirculated to the intake passage 20 . One end of the EGR passage 40 is connected to the exhaust passage 30 and the other end of the EGR passage 40 is connected to the intake passage 20 on the downstream side of the surge tank 23 . An EGR valve 41 is provided in the middle of the EGR passage 40 for controlling the exhaust gas recirculation amount by opening and closing the EGR passage 40 .

The engine system 100 also includes an ECU (Electronic Control Unit) 200 . The ECU 200 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a storage device, and the like. The ECU 200 executes an EGR gas flow rate calculation process, which will be described later, by executing a program stored in the ROM or storage device. The ECU 200 is an example of a first determination section, a second determination section, and a control section.

Various actuators such as the fuel injector 15, the spark plug 16, the throttle valve 22, and the EGR valve 41 are connected to the output side of the ECU 200. FIG. The ECU 200 includes various sensors such as the air flow meter 21, the exhaust pressure sensor 32, the crank angle sensor 19, the accelerator position sensor 44, the water temperature sensor 52, and a cylinder pressure sensor for detecting the cylinder pressure to detect the operating state of the engine. and various information and signals related to operating conditions are input. The ECU 200 calculates the flow rate of the EGR gas based on the information and signals described above, and controls the EGR valve 41 so as to achieve the flow rate.

Here, an example of a conventional method for calculating the EGR gas flow rate when the internal combustion engine 10 has the exhaust purification catalyst 31 will be described. Note that the ECU that executes the conventional EGR gas flow rate calculation method will be described as the ECU 200A.

The ECU 200A detects particulate matter (hereinafter referred to as PM) deposited on the exhaust purification catalyst 31 based on the intake air amount (GA) input from the air flow meter 21 and the exhaust pressure input from the exhaust pressure sensor 32. ) (deposited amount of PM) is acquired. For example, the ECU 200A acquires the PM deposition amount in the exhaust purification catalyst 31 using a map for determining the PM deposition amount from the intake air amount (GA) and the exhaust pressure shown in FIG. 2(A). Each line in FIG. 2(A) represents the amount of deposited PM. Then, the ECU 200A calculates the EGR gas flow rate from a map for obtaining the EGR gas flow rate from the exhaust pressure shown in FIG. Note that in the map shown in FIG. 2(B), the EGR gas flow rate is defined with respect to the exhaust pressure so as not to cause misfiring or deteriorated durability (OT) of intake system parts.

FIG. 3(A) is an enlarged map of the intake air amount range of 0 to 20 [g/s] in FIG. 2(A). As shown in FIG. 3A, in a region where the amount of intake air is small (low GA region), when the exhaust pressure fluctuates by 1 kPa, the amount of accumulated PM also fluctuates greatly. Considering the measurement variation (about ±1 kPa) of the exhaust pressure sensor 32, the calculation accuracy is low in the low GA region, so the map shown in FIG. 2A cannot be used to calculate the PM deposition amount. Therefore, as shown in FIG. 3B, the ECU 200A calculates the EGR gas flow rate using a map in which the low GA region is masked.

However, if the internal combustion engine 10 continues to operate in the low GA range, PM continues to accumulate without knowing how much PM is accumulated in the exhaust purification catalyst 31 (the degree of PM clogging), and the exhaust pressure rises. . As a result, the EGR gas flow rate becomes excessive, causing misfiring and deteriorating the durability of intake system parts.

Therefore, in the present embodiment, while the internal combustion engine 10 is operating in the low GA range, the ECU 200 estimates the PM deposition amount and calculates the EGR gas flow rate from the estimated PM deposition amount.

FIG. 4 is a flowchart of the EGR gas flow rate calculation process executed by the ECU 200. As shown in FIG.

First, the ECU 200 determines whether or not the intake air amount is smaller than the first threshold value (step S11). In this step, it is determined whether or not the internal combustion engine 10 is operating in the low GA range.

If the intake air amount is smaller than the first threshold value (step S11/YES), the ECU 200 calculates the amount of PM deposited on the exhaust purification catalyst 31 from the start of the operation of the internal combustion engine 10 in the low GA region to the present time ( PM deposition change amount) is calculated (step S13). For example, the ECU 200 determines the fuel injection amount based on the rotational speed and load factor of the internal combustion engine 10 calculated from the outputs of the crank angle sensor 19 and the accelerator position sensor 44 and the cooling water temperature input from the water temperature sensor 52. Calculate The ECU 200 estimates the amount of PM deposited on the exhaust purification catalyst 31 based on the calculated fuel injection amount. The ECU 200 accumulates the estimated amount of PM to calculate the PM accumulation change amount.

Subsequently, the ECU 200 calculates the sum of the PM amount (estimated value) accumulated in the exhaust purification catalyst 31 before the internal combustion engine 10 is operated in the low GA region and the PM accumulation change amount calculated in step S13 (PM estimated amount of deposition) is calculated (step S15).

Next, the ECU 200 calculates the EGR gas flow rate using the map that defines the relationship between the PM estimated deposition amount and the EGR gas flow rate shown in FIG. 5 (step S17).

By the way, if the intake air amount is equal to or greater than the first threshold value (step S11/NO), the internal combustion engine 10 is operating in the normal region. Therefore, in this case, the ECU 200 uses the exhaust pressure to calculate the EGR gas flow rate (step S21). Specifically, the ECU 200 acquires the PM accumulation amount from the intake air amount and the exhaust pressure in the map shown in FIG. EGR gas flow rate is calculated using a map (see FIG. 2(B)) defining the relationship between (step S21).

After completing step S17 or S21, the ECU 200 updates the EGR gas flow rate to the calculated EGR gas flow rate (step S19).

Next, the ECU 200 changes the opening degree of the EGR valve 41 so as to realize the updated EGR gas flow rate (step S21), and ends the processing of FIG. For example, in the process of step S17, the EGR gas flow rate is maintained when the estimated PM deposition amount is greater than the second threshold indicated by the dotted line in the map shown in FIG. In this case, since the exhaust pressure is rising due to PM deposition, the ECU 200 reduces the opening of the EGR valve 41 in order to maintain the EGR gas flow rate.

As described above in detail, the engine system 100 according to the present embodiment includes an EGR passage 40 that recirculates part of the exhaust gas from the exhaust passage 30 of the internal combustion engine 10 to the intake passage 20 of the internal combustion engine 10 as EGR gas, An EGR valve 41 provided on the EGR passage 40 for adjusting the flow rate of EGR gas, an exhaust purification catalyst 31 provided on the exhaust passage 30 for collecting particulate matter in the exhaust, and intake air of the internal combustion engine 10. and an exhaust pressure sensor 32 for detecting the pressure in the exhaust passage 30 on the upstream side of the exhaust purification catalyst 31 as the exhaust pressure. Further, when the intake air amount is less than the first threshold, the engine system 100 has the estimated amount of PM deposited on the exhaust purification catalyst 31 after the intake air amount becomes less than the first threshold, and the intake air amount is equal to the first threshold. The flow rate of EGR gas is determined based on the sum of the estimated amount of PM deposited on the exhaust purification catalyst 31 before becoming less than the first threshold value, and when the intake air amount is equal to or greater than the first threshold value, the EGR gas flow rate is calculated based on the exhaust pressure , and controls the opening of the EGR valve 41 in accordance with the determined flow rate of the EGR gas. As a result, even in the low GA range, the EGR gas flow rate can be accurately determined based on the PM estimated deposition amount, so that an appropriate amount of EGR gas can be recirculated. Therefore, it is possible to suppress the occurrence of deterioration of combustion such as misfiring and the deterioration of the durability of intake system parts due to high-temperature EGR gas.

The above-described embodiments are merely examples for carrying out the present invention, and the present invention is not limited to these, and various modifications of these examples are within the scope of the present invention, and furthermore, It is self-evident from the above description that many other embodiments are possible within the scope.

10 internal combustion engine 20 intake passage 21 air flow meter (intake air amount detector)
30 exhaust passage 31 exhaust purification catalyst (particulate filter)
32 exhaust pressure sensor (exhaust pressure detector)
40 EGR passage 41 EGR valve 100 engine system (control device for internal combustion engine)
200 ECU (first decision unit, second decision unit, control unit)

Claims (2)

an EGR passage that recirculates part of the exhaust gas from the exhaust passage of the internal combustion engine to the intake passage of the internal combustion engine as EGR (Exhaust Gas Recirculation) gas;
an EGR valve provided on the EGR passage for adjusting the flow rate of the EGR gas;
a particulate filter that is provided on the exhaust passage and collects particulate matter in the exhaust;
an intake air amount detection unit that detects an intake air amount of the internal combustion engine;
an exhaust pressure detection unit that detects the pressure in the exhaust passage on the upstream side of the particulate filter as the exhaust pressure;
a PM deposition amount estimating unit that estimates the amount of PM deposited on the particulate filter based on the fuel injection amount;
When the intake air amount is less than the first threshold, the estimated amount of PM accumulated in the particulate filter after the intake air amount becomes less than the first threshold and the amount before the intake air amount becomes less than the first threshold a first determination unit that determines a first target value of the flow rate of the EGR gas based on the sum of the estimated amount of PM deposited on the particulate filter and
a second determination unit that determines a first target value for the flow rate of the EGR gas based on the exhaust pressure when the intake air amount is equal to or greater than a first threshold;
a control unit that controls the degree of opening of the EGR valve according to the determined first target value of the flow rate of the EGR gas;
A control device for an internal combustion engine. an EGR passage that recirculates part of the exhaust gas from the exhaust passage of the internal combustion engine to the intake passage of the internal combustion engine as EGR (Exhaust Gas Recirculation) gas;
an EGR valve provided on the EGR passage for adjusting the flow rate of the EGR gas;
a particulate filter that is provided on the exhaust passage and collects particulate matter in the exhaust;
an intake air amount detection unit that detects an intake air amount of the internal combustion engine;
an exhaust pressure detection unit that detects the pressure in the exhaust passage on the upstream side of the particulate filter as the exhaust pressure;
a PM deposition amount estimating unit that estimates the amount of PM deposited on the particulate filter based on the load factor of the internal combustion engine;
When the intake air amount is less than the first threshold, the estimated amount of PM accumulated in the particulate filter after the intake air amount becomes less than the first threshold and the amount before the intake air amount becomes less than the first threshold a first determination unit that determines a target value of the flow rate of the EGR gas based on the sum of the estimated amount of PM deposited on the particulate filter and
a second determination unit that determines a target value for the flow rate of the EGR gas based on the exhaust pressure when the intake air amount is equal to or greater than a first threshold;
a control unit that controls the degree of opening of the EGR valve according to the determined target value of the flow rate of the EGR gas;
A control device for an internal combustion engine.

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