KR102452681B1 - Method for reducing exhaust gas of engine in case of controlling scavenging - Google Patents

Abstract

The present invention relates to a control method capable of reducing exhaust gas during scavenging control, comprising the steps of: determining whether a current engine state enters a scavenging region in an overlapping section between an intake valve and an exhaust valve; determining whether an oxygen storage capacity (OSC) of a catalyst for exhaust gas purification disposed in an exhaust passage of an engine is deteriorated to less than a predetermined threshold value; When it is determined that the oxygen intake/release capability of the catalyst is deteriorated below the threshold value, the air-fuel ratio control of the engine is performed based on the air-fuel ratio (lambda) value at the catalyst position.

Description

Exhaust gas reduction method at the time of scavenging control of an engine

The present invention relates to a method for reducing exhaust gas during scavenging control of an engine, and in particular, in a scavenging (scavenging) state in which new components are directly transferred from an intake port of an engine to an exhaust port of an engine, harmful gas removal through air-fuel ratio control It relates to a control method capable of reducing exhaust gas by preventing the deterioration of the function of the catalyst.

Recently, an engine having a turbocharger and an intercooler has been in the spotlight to reduce fuel consumption and obtain greater output. In such an internal combustion engine, exhaust gas or external air is sucked in and compressed by a compressor of a turbocharger, and the generated supercharged air is supplied to the engine side.

In an engine with such a turbocharger, the supercharged air that has passed through the supercharger is supplied to the combustion chamber inside the cylinder of the engine through the intake port, and the exhaust gas burned in the combustion chamber is discharged through the exhaust port.

However, in the case of an engine having such a turbocharger, a region in which the intake pressure at the intake port is greater than the exhaust pressure at the exhaust port occurs due to the increase of the boost pressure in the low-speed and high-load region during operation. In this case, in a section where the intake valve and the exhaust valve overlap, a phenomenon in which the fresh air component supplied through the intake port is directly transferred to the exhaust port occurs.

As disclosed in Patent Document 1, under such a scavenging state, the scavenging efficiency increases and the amount of residual gas in the combustion chamber decreases, so that the fuel filling efficiency is increased and the torque is improved.

Patent Document 1: Unexamined Patent Publication No. 2013-0020600 (2013.2.27)

FIG. 2 discloses a method of controlling the air-fuel ratio of the engine during scavenging control of the engine. In this control method, it is first determined whether the state of the engine is in the scavenging control region (S10), and when it is in the scavenging control region, the lambda value inside the combustion chamber is based on the amount of air bypassed without staying in the cylinder of the engine. to perform air-fuel ratio control (S20).

However, as fresh air containing a large amount of oxygen is bypassed directly to the exhaust manifold during scavenging air control, a large amount of oxygen is instantaneously filled inside the catalyst. lose the ability to

Therefore, if the control is performed in the above manner, catalyst loss can be prevented, but a phenomenon in which the exhaust gas purification ability is deteriorated occurs because it causes rapid oxygen storage of the catalyst.

An object of the present invention is to improve the problem of emission of harmful substances in exhaust gas that may occur while performing scavenging control.

The present invention for solving the above problems, in the overlap section of the intake valve and the exhaust valve, determining whether the current state of the engine has entered a scavenging (scavenging) region; determining whether an oxygen storage capacity (OSC) of a catalyst for exhaust gas purification disposed in an exhaust passage of an engine is deteriorated to less than a predetermined threshold value; When it is determined that the oxygen intake/release capability of the catalyst is deteriorated below the threshold value, the air-fuel ratio control of the engine is performed based on the air-fuel ratio (lambda) value at the catalyst position.

accumulating the air filling amount in the cylinder of the engine from a point in time when the oxygen intake/release capability of the catalyst preferably falls below the threshold value; The method further comprises the step of determining whether an integrated air filling amount exceeds a predetermined reference value, wherein when the integrated air filling amount exceeds a predetermined reference value, based on the air-fuel ratio (lambda) value at the catalyst position Perform air-fuel ratio control.

Preferably, when the accumulated air filling amount is less than a predetermined reference value, the lambda value inside the combustion chamber is calculated using the actual air filling amount inside the combustion chamber of the engine, and the air-fuel ratio control of the engine is performed based on this lambda value gksek

Preferably, the air-fuel ratio value at the catalyst position is measured by an oxygen sensor installed upstream of the catalyst.

In another preferred embodiment according to the present invention for solving the above problems, in an overlapping section between the intake valve and the exhaust valve, determining whether the current engine state has entered a scavenging region; determining the degree of catalyst deterioration by comparing an oxygen storage capacity (OSC) of a catalyst for exhaust gas purification disposed in an exhaust passage of an engine and a predetermined threshold value; accumulating the air filling amount in the cylinder of the engine from the point in time when the oxygen intake/release capability of the catalyst deteriorates below the threshold value; determining whether the accumulated air filling amount exceeds a predetermined reference value; and performing purging control of the catalyst by richly injecting fuel into the combustion chamber of the engine when the accumulated amount of air filling exceeds a predetermined reference value.

According to the present invention, it is possible to prevent deterioration of the exhaust gas purifying ability of the catalyst during scavenging control, thereby effectively reducing the harmful gas contained in the exhaust gas.

According to the present invention, it is possible to actively use the scavenging air control without the problem of catalyst deterioration, so that drivability such as increase of output torque can be enhanced.

1 is a diagram schematically illustrating an example of a configuration of a turbo engine system that can be applied to a control method according to an embodiment of the present invention.
2 is a flowchart related to an air-fuel ratio control method at the time of scavenging.
3 is a flowchart illustrating a preferred embodiment according to the present invention.
4 is a flowchart illustrating another preferred embodiment according to the present invention.

A preferred embodiment of the present invention will be described in detail based on the accompanying drawings as follows.

1 is a diagram schematically illustrating an example of a configuration of a turbo engine system that can be applied to a control method for reducing exhaust gas during scavenging control according to an embodiment of the present invention.

First, outside air is supplied into the turbo engine system, and the inflow of the supplied outside air is preferably measured through a hot film mass air flow (HFM) sensor. The introduced outside air is compressed and supercharged by the compressor 10 of the turbocharger. And the supercharged air is cooled to a predetermined temperature by the intercooler 50 . The boost pressure, which means the pressure at the rear end of the compressor 10, is obtained by measuring the air cooled by the intercooler 50 by the boost pressure sensor.

Air cooled through the intercooler 50 is introduced into the carburetor to form a mixture with the fuel supplied from the fuel tank 120 . The amount of air supplied to the carburetor is regulated by the throttle valve 130 . The mixture mixed with fuel is supplied to the combustion chamber inside the cylinder 90 of the engine and burned according to the operation of the piston 80 and the intake valve 60 inside the cylinder. The intake air pressure into the combustion chamber is preferably measured with a MAP (Manifold Absolute Pressure) sensor.

The exhaust gas generated by combustion in the combustion chamber inside the cylinder 90 is discharged from the inside of the cylinder 90 by the operation of the exhaust valve 70 . A part of the exhaust gas discharged here is introduced into the turbine 20 of the turbocharger to rotate the turbine 20, and as described above by the compressor 10 coaxially connected to the turbine 20, to supercharge the new air. do. And, the amount of exhaust gas flowing into the turbine 20 is controlled by adjusting the opening degree of a waste gate valve (WGV) 40 by a waste gate actuator (WGA) 30 . Specifically, as the opening degree of the WGV 40 decreases, the flow rate of the exhaust gas supplied to the turbine 20 among the total exhaust gas flow rate increases.

The exhaust gas is post-processed by a manifold catalytic converter (MCC) 100, an underbody catalytic converter (UCC) 110, etc. and then discharged to the outside of the vehicle. do.

In addition, an intake-side pressure sensor 140 and an exhaust-side pressure sensor 150 for sensing intake-side and exhaust-side pressures are provided inside the intake port and exhaust port of the engine, respectively. In addition, a first oxygen sensor 160 and a second oxygen sensor 170 are provided at the front and rear ends of the catalysts 100 and 110 for removing harmful gas from the exhaust side, respectively.

3 is a flowchart illustrating a preferred embodiment according to the present invention. According to FIG. 3 , a controller (eg, an electronic control unit (ECU)) not shown determines whether the current engine is in the scavenging state ( S100 ).

In the scavenging air state, the pressure in the intake port is higher than the pressure in the exhaust port, so that a phenomenon occurs in which fresh air is directly transferred from the intake port 12 to the exhaust port 13 . Accordingly, the pressure value of the intake port affects the presence or absence of the scavenging state. In addition, scavenging occurs in a valve overlap state in which both the intake port and the exhaust port are open.

In addition, in the case of an engine having a turbocharger, it enters a skiing state in a low-speed, high-load region. Accordingly, the rotational speed of the engine also affects the judgment as to whether the engine is under the scavenging condition. And, under the scavenging state, the unburned fuel increases in the combustion chamber, and a change occurs in the combustion state. Accordingly, the temperature of the engine also affects the determination of whether the scavenging state is present.

Therefore, preferably, the controller collects information about the valve timing control amount, the rotational speed (RPM) of the engine, the temperature of the engine, and the pressure of the intake port, and combines at least two or more of these information, thereby determine whether the state is

When it is determined that the engine is in the scavenging control region, the controller determines whether the oxygen intake/release capability of the catalyst has reached a predetermined threshold ( S110 ).

To this end, the controller determines the delay time from the time when the signal of the first oxygen sensor 160 moves upward to the time when the signal of the second oxygen sensor 170 installed on the downstream side of the catalysts 100 and 110 moves upward. The oxygen absorption/release capability (OSC) of the catalysts 100 and 110 to be determined is detected. That is, when the air-fuel ratio is changed from lean to rich, the first oxygen sensor 160 installed on the upstream side of the catalyst and the second oxygen sensor 170 installed on the downstream side of the catalyst according to the degree of deterioration of ceria, which is a constituent material of the catalyst, ), using the principle that the time delay is different, the oxygen absorption/release capability (OSC) is detected, and this is compared with a predetermined limit value.

When it is determined that the oxygen storage capacity of the catalysts 100 and 110 is no longer the oxygen absorption/release capacity of the current catalysts 100 and 110 exceeds a predetermined limit, as will be described later, based on the lambda value at the catalyst position The air-fuel ratio is controlled (S150).

On the other hand, in the present invention, preferably, before the air-fuel ratio control is performed based on the lambda value at the catalyst position, after the oxygen intake/release capacity of the catalysts 100 and 110 exceeds a predetermined limit, the air inside the cylinder 90 of the engine The charging amount is accumulated (S120) and compared with a predetermined reference value (S130).

The reason that whether or not to control the air-fuel ratio based on the lambda value at the catalyst position is based on the air filling amount of the cylinder 90 is that the amount of gas burned in the engine is the main factor of exhaust gas, and the value determining it is 90) because of the air charge. When the amount of air filling exceeds a certain value, it means that the element that generates exhaust gas exceeds a certain value, which is because there is a risk that a lot of exhaust gas and harmful components contained therein are generated due to combustion of a certain flow rate or more.

Meanwhile, in order to obtain the air filling amount in the cylinder 90 , the controller uses the intake/exhaust pressure difference and the valve overlap measured using the intake-side pressure sensor 140 and the exhaust-side pressure sensor 150 to determine the amount of air filling. The flow rate of fresh air that is directly bypassed to the port is calculated, and the amount of fresh air in the combustion chamber of the cylinder 90 is calculated based on the remaining amount of air except for this value, and this is integrated.

Next, the controller determines whether the accumulated air filling amount in the combustion chamber of the cylinder 90 exceeds a reference value (S130), and when this value is exceeded, it is determined that there is a risk of contamination due to the mass generation of exhaust gas Accordingly, the air-fuel ratio of the engine is controlled based on the lambda value at the catalyst position (150).

The lambda value at the catalyst location preferably uses a value measured by the first oxygen sensor 160 positioned upstream of the catalysts 100 and 110 . When the air-fuel ratio control is performed based on the lambda value of the catalyst position, the oxygen sensor measurement value is sparse due to the influence of oxygen in the fresh air flowing into the catalyst after bypassing, and based on this value, it is determined that the fuel in the combustion chamber is lean. It makes a judgment, and this results in a rich injection of fuel.

Then, the fuel is injected richly into the cylinder 90 to flow the fuel into the exhaust system.

When sent, this causes intended post-combustion to remove oxygen stored in the catalysts 100 and 110. Accordingly, all of the oxygen adsorbed in the catalysts 100 and 110 is removed, so that the catalysts 100 and 110 can purify the exhaust gas normally again.

On the other hand, when the accumulated air filling amount in the combustion chamber of the cylinder 90 does not exceed the reference value, the controller determines that it is not necessary to perform control for recovering the performance of the catalysts 100 and 110, so that the combustion chamber lambda An air-fuel ratio control is performed based on the value (S140).

At this time, the controller calculates the flow rate of fresh air that is directly bypassed to the exhaust port based on the intake/exhaust pressure difference and the degree of valve overlap measured using the intake-side pressure sensor 140 and the exhaust-side pressure sensor 150 . and calculates the amount of air in the combustion chamber of the cylinder 90 based on the amount of air remaining except for this value, and controls the air-fuel ratio based on this. In this case, the fuel is injected based on the calculated air amount excluding the bypassed air flow rate.

4 is a flowchart illustrating another preferred embodiment according to the present invention. Comparing the embodiment shown in FIG. 4 with the embodiment shown in FIG. 3 , only the control method when the accumulated air filling amount in the combustion chamber of the cylinder 90 exceeds the reference value is different. Accordingly, duplicate description will be omitted and only differences from the embodiment shown in FIG. 3 will be mainly described.

According to the embodiment shown in FIG. 4 , it is determined whether the accumulated air filling amount in the combustion chamber of the cylinder 90 exceeds a reference value (S230), and when the reference value is exceeded, catalyst purge control is performed (S250).

That is, the controller temporarily sets the target lambda value to be rich, whereby unburned combustion is transferred to the catalysts 100 and 110 to be post-burned together with oxygen. According to this embodiment of the present invention, it is possible to intentionally and more actively solve the performance degradation of the catalysts 100 and 110 .

10: compressor 20: turbine
30: waste gate actuator (WGA) 40: waste gate valve (WGV)
50: intercooler 60: intake valve
70: exhaust valve 80: piston
90: cylinder 100: manifold type catalytic converter (MCC)
110: underbody type catalytic converter (UCC) 120: fuel tank
130: throttle valve 140: intake side pressure sensor
150: exhaust side pressure sensor 160: first oxygen sensor
170: second oxygen sensor

Claims (5)

determining whether a current engine state has entered a scavenging region in an overlapping section of the intake valve and the exhaust valve;
determining whether an oxygen storage capacity (OSC) of a catalyst for purifying exhaust gas disposed in an exhaust passage of the engine has deteriorated to less than a predetermined threshold value;
When it is determined that the oxygen intake/release capability of the catalyst is deteriorated below the threshold value, the air-fuel ratio control of the engine is performed based on the air-fuel ratio (lambda) value at the catalyst position,
accumulating the air filling amount in the cylinder of the engine from the point in time when the oxygen intake/release capability of the catalyst falls below the threshold value;
Further comprising the step of determining whether the accumulated air filling amount exceeds a predetermined reference value,
The method for reducing exhaust gas during scavenging control of an engine, characterized in that when the accumulated air filling amount exceeds a predetermined reference value, the air-fuel ratio control of the engine is performed based on an air-fuel ratio (lambda) value at the catalyst position. determining whether a current engine state has entered a scavenging region in an overlapping section of the intake valve and the exhaust valve;
determining the degree of catalyst deterioration by comparing the oxygen storage capacity (OSC) of the catalyst for exhaust gas purification disposed in the exhaust passage of the engine with a predetermined threshold value;
accumulating the air filling amount in the cylinder of the engine from the point in time when the oxygen intake/release capability of the catalyst deteriorates to less than the threshold value;
determining whether the accumulated air filling amount exceeds a predetermined reference value;
and performing purging control of the catalyst by richly injecting fuel into the combustion chamber of the engine when the accumulated air charging amount exceeds a predetermined reference value. How to reduce gas. delete 3. The method according to claim 2,
When the accumulated air filling amount is less than a predetermined reference value,
A method for reducing exhaust gas during scavenging control of an engine, comprising calculating a lambda value inside the combustion chamber by using an actual air filling amount inside the combustion chamber of the engine, and controlling the air-fuel ratio of the engine based on the lambda value. The method according to claim 1,
The method for reducing exhaust gas during scavenging control of an engine, characterized in that the air-fuel ratio value at the catalyst position is measured by an oxygen sensor installed on an upstream side of the catalyst.

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