KR102429054B1 - Method for controlling catalyst light-off time activity of engine using idle stop and go system - Google Patents

Abstract

The present invention relates to a method for controlling catalyst activation of an internal combustion engine employing an ISG system. In the present invention, when at least any one of the temperature of the exhaust system, the amount of heat in the exhaust, and the catalyst heating time is equal to or greater than each predetermined first threshold value, the engine is stopped by performing idle stop control, and the first threshold value at this time is set to the value of the catalyst. By setting it to be changed according to the degree of degradation, it is characterized in that it is decided whether to stop and restart the engine in consideration of the degree of degradation of the catalyst.

Description

A method for controlling catalyst activation in an internal combustion engine employing an ISG system

The present invention relates to a catalyst activation control method for an internal combustion engine employing an ISG system, and more particularly, to a catalyst activation control method for performing idle stop control in consideration of the degree of catalyst deterioration.

As shown in FIG. 1 , the engine 10 of the vehicle sucks outside air from the intake system 20 provided on the upstream side of the intake port 12 , and passes through the intake valve 14 and the intake port 12 . , is supplied to the combustion chamber 11 inside the cylinder 16 of the engine 10 .

External air supplied from the intake port 12 is mixed with fuel supplied through a fuel injection valve (not shown) to form a mixture and is combusted in the combustion chamber 11 , and exhaust gas after combustion is exhausted through the exhaust valve 15 and exhaust gas. It is discharged to the exhaust system through port 13.

A catalyst device 40 is provided downstream of the exhaust port 13 . The catalyst device 40 is a post-processing device that removes harmful gas and particulate harmful substances including soot included in exhaust gas.

As described above, the catalyst provided in the catalyst device 40 is a device that converts harmful components in the exhaust gas into harmless components by redox action and discharges them, and plays an important role in preventing air pollution.

However, in order for the catalyst to perform a purification action, the activation temperature must be reached. At the initial start of the engine or during idle driving with a low engine speed, the catalyst is not heated enough and it is difficult to exert its function due to heat radiation through the case.

To this end, Patent Document 1 discloses a technique for rapidly increasing the temperature of the catalyst by introducing a part of the exhaust gas into the case of the catalytic converter so as to shorten the activation time of the catalyst in order to improve the purification ability of the catalyst.

On the other hand, in recent years, the number of vehicles employing an Idle Stop&Go (ISG) system as in Patent Document 2 is increasing in order to meet the demand for fuel efficiency improvement. The idle stop & go system automatically stops the engine after a few seconds after the vehicle is stopped to improve fuel efficiency, for example, about 3 seconds after the vehicle speed signal is zero and the brake pedal is pressed. For example, when a brake pedal is released or a gear is shifted, the system starts automatically without operation of the ignition key.

Patent Document 1: Republic of Korea Patent Publication No. 10-2013-0005739 (22013-0005739) Patent Document 2: Republic of Korea Registered Patent No. 10-0551306 (Jun. 10, 2006)

As described above, the catalyst used in the internal combustion engine needs to be activated at a certain temperature or higher to ensure the efficiency of purifying the exhaust gas. In addition, high-temperature exhaust gas generated during fuel combustion is actively utilized for early activation of the catalyst. However, in the case of an ISG system, which has been rapidly applied to improve fuel efficiency, it is impossible to actively utilize catalyst heating control for catalyst activation when the engine is stopped for fuel efficiency improvement.

Therefore, in an internal combustion engine including an ISG system, when the catalyst is not sufficiently heated for heating control for catalyst activation, it is preferable not to stop the engine even in the idle section.

However, since the catalyst activation temperature is different when the catalyst is new and when the catalyst is degraded by the use of a certain amount of catalyst, when determining whether to idle the ISG system (engine stop) without considering the deterioration degree of the catalyst, There is a risk that the fuel economy saving effect will be halved.

The present invention has been devised to solve the above problems, and an object of the present invention is to determine whether to perform an idle stop in consideration of the degree of catalyst deterioration, a method for controlling catalyst activation of an internal combustion engine employing an ISG system is to provide

In a method for controlling catalyst activation of an internal combustion engine employing an ISG system according to the present invention for solving the above problems, at least one of an exhaust system temperature, an exhaust heat amount, and a catalyst heating time is greater than or equal to each predetermined first threshold value In this case, idle stop control is performed to stop the engine, and the first threshold value at this time is set to be changed according to the degree of degradation of the catalyst, so that whether to stop and restart the engine is decided in consideration of the degree of degradation of the catalyst. do it with

More preferably, the first threshold value is set to increase/decrease a preset fixed value at a predetermined rate according to the deterioration degree of the catalyst.

More preferably, after stopping the engine, when the temperature of the exhaust system, the amount of heat of the exhaust, and the catalyst heating time become less than each of the predetermined second threshold values, the engine is restarted.

More preferably, the second threshold value is set to be changed by the degree of degradation of the catalyst.

More preferably, the temperature of the exhaust system is the catalyst temperature or the temperature of the exhaust gas.

More preferably, the catalyst heating time is a time for heating the catalyst by increasing the temperature of the exhaust gas through the valve overlap of the intake valve and the exhaust valve of the engine.

More preferably, the catalyst heating time is a time for heating the catalyst by heating the exhaust gas by a separate exhaust gas heater installed on the exhaust system.

More preferably, the catalyst heating time is a time for heating the catalyst by heating the exhaust gas by generating recombustion of the exhaust gas on the upstream side of the catalyst in the exhaust system.

More preferably, it is determined whether the catalyst heating time before the engine is stopped is equal to or less than a predetermined minimum holding time, and thus, whether to heat the catalyst after restarting the engine.

More preferably, the minimum holding time of the catalyst heating is determined as a function of the catalyst deterioration degree.

More preferably, the degree of degradation of the catalyst is determined based on the oxygen absorption/release capability (OSC) of the catalyst.

More preferably, the oxygen absorption/release capability of the catalyst is measured using a time delay between oxygen sensors installed on the upstream and downstream sides of the catalyst.

More preferably, the deterioration degree of the catalyst is determined based on the exhaust gas temperature measured at the rear end of the catalyst.

More preferably, the information on the temperature of the exhaust system, the amount of exhaust heat and the catalyst heating holding time is corrected according to the time elapsed after the stop of the engine.

Advantageous Effects of Invention According to the present invention, it is possible to provide a catalyst activation control method that satisfies recent stringent emission gas regulations through optimal control in consideration of catalyst activation in an engine employing an ISG system.

In addition, according to the present invention, it is possible to provide an optimal control method that satisfies both the catalyst activation for satisfying the emission gas regulation standards and the engine stop request by the ISG for improving fuel efficiency, thereby improving fuel efficiency compared to the prior art. It works.

1 is a diagram schematically showing the configuration of an internal combustion engine having an intake system and an exhaust system;
2 is a block diagram schematically showing a system for performing a method for controlling catalyst activation of an internal combustion engine employing an ISG system according to the present invention;
3 is a flowchart showing a preferred embodiment of a method for controlling catalyst activation of an internal combustion engine employing an ISG system;
4 is a view showing the difference between catalyst heating of a new product and a deteriorated catalyst when the engine is restarted after stopping the engine when the catalyst activation control method according to the present invention is applied.

Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram schematically illustrating a system for performing a method for controlling catalyst activation of an internal combustion engine employing an ISG system according to the present invention.

The internal combustion engine illustrated in FIG. 2 is an engine 10 serving as a power source of a vehicle, and refers to a diesel engine or a gasoline engine. The engine 10 according to the present invention employs an ISG system to improve fuel efficiency. The ISG system is network-connected with the engine controller (ECU) and includes an Integrated Generator Starter (IGS) for the ISG system that performs engine starting and charging functions. When a predetermined idle stop condition is satisfied, for example, the vehicle When a certain time elapses after stopping, the engine is stopped according to the control command of the engine controller. After that, when a driving intention is sensed by the driver, for example, when a brake pedal is released or a gear is changed, the engine is automatically started using the ISG system ISG system starter generator.

The engine controller controls the engine 10 to perform catalyst heating for catalyst activation, while controlling the ISG system to stop and restart the engine when a predetermined condition is satisfied.

In addition, information about the amount of air sucked into the intake system 20 of the engine 10, the RPM of the engine 10, and the air-fuel ratio is measured by various sensor equipment provided in the engine 10 and transmitted to the engine controller, It will be used for catalytic heating control or ISG control. In addition, information such as the position of the accelerator pedal or the vehicle speed is transmitted to determine the driver's intention to drive or stop, and the information is used for the catalyst heating control or ISG control described above.

3 is a flowchart illustrating a preferred embodiment of a method for controlling catalyst activation of an internal combustion engine employing an ISG system according to the present invention.

Referring to FIG. 3 , the engine controller first determines whether the driving state of the engine 10 satisfies an idle stop condition ( S10 ). As described above, the idle stop is normally performed when the vehicle speed signal is zero and a predetermined time has elapsed from the state in which the brake pedal is depressed. Accordingly, it is possible to determine whether the idle stop condition is satisfied by detecting the vehicle speed signal and the brake operation state. On the other hand, even when the above-described basic idle stop condition is satisfied, the idle stop may be limited when the vehicle's battery charging voltage is remarkably low. The engine controller determines whether the idle stop condition is satisfied in consideration of the above-described special condition as well.

When it is determined in step S10 that the idle stop condition is satisfied, the engine controller detects the deterioration degree of the current catalyst 40 (S20).

The degree of degradation of the catalyst 40 may be determined in various ways. For example, according to a preferred embodiment of the present invention, the degree of deterioration of the catalyst 40 is determined based on the oxygen absorption/release capability (OSC) of the catalyst 40 . When the air-fuel ratio is changed from lean to rich, the measurement time of the first oxygen sensor installed on the upstream side of the catalyst 40 and the second oxygen sensor installed on the downstream side of the catalyst according to the degree of deterioration of ceria, which is a constituent material of the catalyst, is A time delay will occur. Using this, the engine controller determines the delay time from the time when the signal of the first oxygen sensor moves upward to the time when the signal of the second oxygen sensor installed on the downstream side of the catalyst 40 moves upward. Oxygen absorption and emission capacity (OSC) of the can be detected. And by comparing this with the reference value, the deterioration degree of the catalyst can be calculated as a percentage ratio.

Meanwhile, according to another preferred embodiment of the present invention, the degree of degradation of the catalyst may be determined based on the exhaust gas temperature measured at the rear end of the catalyst 40 .

In the case of the catalyst 40, the main cause of deterioration is thermal deterioration due to high temperature exposure. Accordingly, by calculating the amount of heat load applied to the catalyst 40 using the time and temperature at which the catalyst 40 is exposed, the degree of deterioration of the catalyst may be calculated as a percentage ratio.

After obtaining the degradation degree of the catalyst through the above-described method, the engine controller determines whether the ISG system performs an idle stop operation, that is, whether the engine is stopped, using the calculated degradation degree of the catalyst.

To this end, the engine controller determines whether at least one of the temperature of the exhaust system, the amount of heat in the exhaust, and the catalyst heating time exceeds each predetermined threshold ( S30 ). At this time, the temperature of the exhaust system, the amount of heat in the exhaust, and the threshold value of each of the catalyst heating time are values determined as a function of the deterioration degree of the catalyst calculated in step S20.

Here, the temperature of the exhaust system is preferably the temperature of the catalyst itself or the temperature of the exhaust gas. The temperature of the catalyst may be measured through a temperature sensor installed in a catalytic converter or the like. In addition, the temperature of the exhaust gas may be directly detected through a temperature sensor installed in the exhaust system, or may be estimated from a preset map using the engine speed and the engine load.

On the other hand, the heat amount of exhaust can be estimated using the following equation (1).

..식(1)

..Equation (1)

Here, M means the exhaust gas flow rate, Cp is the specific heat of the exhaust gas, Tex is the temperature of the exhaust gas, and Tair is the temperature of the outside air. Each factor in Equation (1) can be obtained by measuring using various sensors installed in the engine or estimating using a preset map.

On the other hand, the catalyst heating time means the time required to heat the catalyst in order to advance the catalyst activation time.

Preferably, the catalyst heating can be achieved by heating the catalyst by increasing the temperature of the exhaust gas using the valve overlap of the intake valve 14 and the exhaust valve 15 of the engine. In a section where the intake valve 14 and the exhaust valve 15 overlap, a phenomenon in which a component of fresh air 30 supplied through the intake port 12 is directly transferred to the exhaust port 13 occurs. In this case, the amount of fresh air 30 delivered to the exhaust port 13 increases, so that the oxygen sensor installed near the catalyst device 40 recognizes that combustion is in a lean state. Due to this determination, the amount of fuel into the combustion chamber is increased, so that the amount of unburned fuel in the combustion chamber 11 is increased. This unburned fuel reacts with the new component to cause post-combustion. It is possible to heat the catalyst 40 due to this post-combustion. Therefore, in this case, the catalyst heating time can be regarded as the valve overlap period of the intake valve 14 and the exhaust valve 15 of the engine.

In addition, preferably, the catalyst heating may be made in the form of directly heating the exhaust gas by a separate exhaust gas heater installed on the exhaust system, such as a hot wire. In this case, the catalyst heating time may be regarded as the driving time of the exhaust gas heater.

In addition, preferably, the catalyst heating may increase the exhaust gas temperature by introducing secondary air into the exhaust system through a separate secondary air introduction device to generate re-combustion upstream of the catalyst, thereby accelerating the catalyst temperature rise. In this case, in this case, the catalyst heating time may be regarded as the time the secondary air is introduced into the exhaust system.

Catalyst heating defined in the present invention is not limited to the above-described examples, and any means or method for heating the catalyst for a predetermined time is included in the catalyst heating of the present invention.

Meanwhile, as described above, the engine controller determines whether at least one of the temperature of the exhaust system, the heat amount of the exhaust, and the catalyst heating time exceeds each predetermined threshold value. Here, the threshold values of the exhaust system temperature, the exhaust heat amount, and the catalyst heating time are values that vary depending on judgment criteria such as the exhaust system temperature, the exhaust heat amount, and the catalyst heating time.

As described above, as the catalyst deteriorates, the temperature required for catalyst activation also increases. Accordingly, the above-described threshold for determining whether catalyst heating is required for catalyst activation may be defined as a function of catalyst degradation. For example, the threshold value may be determined by adding a value obtained by multiplying a predetermined constant by a catalyst degradation degree defined as a percentage ratio to a predetermined value.

Therefore, in the present invention, the engine controller determines whether or not to stop the idle by the ISG system by determining whether at least one of the exhaust system temperature, the exhaust heat amount, and the catalyst heating time is greater than or equal to a threshold value determined as a function of the catalyst deterioration degree. made to do it

The engine controller needs to maintain the On state of the engine 10 for catalyst activation when at least any one of the temperature of the exhaust system, the amount of heat in the exhaust, and the catalyst heating time is greater than or equal to a threshold value determined as a function of the catalyst deterioration degree. It is determined that there is no control, and the engine 10 is stopped to reduce fuel efficiency (S40).

On the other hand, after the engine is stopped, heat loss occurs due to heat transfer from the exhaust system, and the catalyst temperature is reduced. Therefore, in order to reflect this, it is preferable to correct the information on the temperature of the exhaust system, the amount of heat in the exhaust, and the catalyst heating time according to the elapsed time after stopping the engine (S50). For example, correction is performed to reduce the temperature of the exhaust system, the amount of heat in the exhaust, and the catalyst heating time at a certain rate during the engine stop time by using the measurement results by various sensors installed in the engine directly or by using values estimated from a preset map. can do.

Meanwhile, after stopping the engine, the engine controller compares the temperature of the exhaust system, the amount of heat in the exhaust, and the catalyst heating time with a second predetermined threshold value ( S60 ), and after stopping the engine, the temperature of the exhaust system and the amount of heat in the exhaust And, when the catalyst heating time is less than the second threshold, catalyst heating is required to activate the catalyst, and the engine 10 is restarted (S70). Here, like the first threshold value, the second threshold value is set to a different value depending on the temperature of the exhaust system, the amount of heat in the exhaust, and the catalyst heating time, which are the criteria for judgment.

In addition, since the timing at which reheating of the catalyst is required for catalyst activation varies depending on the degree of degradation of the catalyst, the second threshold value is determined as a function of the degree of catalyst degradation in the same manner as the first threshold value. can

Meanwhile, when the engine controller restarts the engine for catalyst activation after the engine is stopped, the engine controller compares the catalyst heating time elapsed so far with a predetermined minimum holding time for catalyst activation (S80). Preferably, the catalyst heating time at this time is a value corrected in consideration of the time elapsed since stopping the engine in step S50.

If the catalyst heating time elapsed so far is less than the predetermined minimum holding time for catalyst activation, catalyst heating is performed until the minimum holding time is reached (S90). On the other hand, the minimum holding time of catalyst heating required for catalyst activation varies depending on the degree of degradation of the catalyst. Accordingly, like the first and second thresholds, the minimum holding time of heating the catalyst of the present invention is also determined as a function of the degree of catalyst deterioration.

4 shows the engine state and the catalyst heating state in a vehicle to which the ISG system is applied when the control method according to the present invention is applied. As can be seen from FIG. 4 , when the catalyst is new and the degree of deterioration is not high, the catalyst heating is maintained even after the engine is restarted. It can be seen that this is maintained for a certain period of time.

According to the above-described preferred embodiment of the present invention, a reference value for determining the engine stop and restart conditions in a vehicle to which the ISG system is applied is defined as a function according to the deterioration degree of the catalyst. Therefore, it is possible to prevent the engine stopping and restarting conditions from being different depending on the degree of deterioration of the catalyst, so that it is unnecessary to prohibit the engine stop for activating the catalyst even in a new product in which the catalyst is hardly used. Also, similarly, it is possible to prevent stopping the engine when the idle stop condition is satisfied, although the engine must be prohibited to be stopped in order to maintain catalyst activation when the catalyst is used for a long period of time and deteriorates considerably.

Accordingly, according to a preferred embodiment of the present invention, it is possible to provide an optimal control method that satisfies both the catalyst activation for satisfying the emission gas regulation standard and the engine stop request by the ISG for improving fuel efficiency.

10: engine 11: combustion chamber
12: intake port 13: exhaust port
14: intake valve 15: exhaust valve
16: cylinder 17: piston
18: connecting rod 20: intake system
21: intake camshaft 22: exhaust camshaft
30: Fresh Air 40: Catalyst device

Claims (15)

A method for controlling catalyst activation of an internal combustion engine employing an ISG system, the method comprising:
determining whether the driving state of the engine satisfies an idle stop condition;
When it is determined that the idle stop condition is satisfied, the oxygen intake/release capability (OSC) of the detected catalyst is compared with the reference value using a time delay between the oxygen sensors installed on the upstream and downstream sides of the catalyst. By doing so, calculating the degradation degree of the catalyst as a percentage ratio;
Calculating a first threshold value by adding a value obtained by multiplying a predetermined constant by a predetermined constant by the degree of deterioration of the catalyst defined as a percentage ratio to a predetermined value related to at least one of the temperature of the exhaust system, the heat amount of the exhaust, and the catalyst heating time;
When at least one of the temperature of the exhaust system, the amount of heat in the exhaust, and the catalyst heating time is equal to or greater than the first threshold value, the ISG system comprising the step of stopping the engine by performing idle stop control. A method for controlling catalyst activation in an internal combustion engine. delete The method according to claim 1,
An internal combustion engine employing an ISG system, characterized in that after stopping the engine, the engine is restarted when the temperature of the exhaust system, the calorific value of the exhaust, and the catalyst heating time become less than the respective second predetermined threshold values. of catalytic activation control method. 4. The method of claim 3,
The method for controlling catalyst activation of an internal combustion engine employing an ISG system, characterized in that the second threshold is set to be changed according to the degree of deterioration of the catalyst. The method according to claim 1,
The catalyst activation control method of an internal combustion engine employing an ISG system, characterized in that the temperature of the exhaust system is a catalyst temperature. The method according to claim 1,
The catalyst activation control method of an internal combustion engine employing an ISG system, characterized in that the temperature of the exhaust system is the temperature of the exhaust gas. The method according to claim 1,
The catalyst activation control method of an internal combustion engine employing an ISG system, characterized in that the catalyst heating time is a time for heating the catalyst by increasing the temperature of the exhaust gas through the valve overlap of the intake valve and the exhaust valve of the engine. The method according to claim 1,
The catalyst activation control method of an internal combustion engine employing an ISG system, wherein the catalyst heating time is a time for heating the catalyst by heating the exhaust gas by a separate exhaust gas heater installed on the exhaust system. The method according to claim 1,
The catalyst activation control method of an internal combustion engine employing an ISG system, wherein the catalyst heating time is a time for heating the catalyst by heating the exhaust gas by generating re-combustion of the exhaust gas on the upstream side of the catalyst in the exhaust system. 4. The method of claim 3,
Catalyst activation control method of an internal combustion engine employing an ISG system, characterized in that it is determined whether the catalyst heating time before the engine is stopped is equal to or less than a predetermined minimum holding time, and then whether or not the catalyst is heated after restarting the engine. 4. The method of claim 3,
The catalyst activation control method of an internal combustion engine employing an ISG system, characterized in that the minimum holding time of the catalyst heating is determined as a function value of the catalyst deterioration degree. delete delete delete 5. The method according to claim 4,
A catalyst activation control method for an internal combustion engine employing an ISG system, wherein information on an exhaust system temperature, an exhaust heat amount, and a catalyst heating holding time is corrected according to a time elapsed after the engine is stopped.

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