KR20220134149A - Control method for decreasing exhaust gas during cold start - Google Patents

Abstract

The present invention relates to an exhaust gas reduction control method during cold start, comprising: an EGR and HSG changing step of gradually opening an EGR and increasing an HSG charging amount together as a set time elapses after starting an engine in a cold status; an EGR and HSG adjusting step of performing the EGR and HSG changing step, determining whether a misfire occurs in the engine, and continuously adjusting an EGR opening rate and an EGR charging amount when the misfire occurs; and an EGR and HSG maintaining step of controlling the corresponding EGR opening rate and the HSG charging amount to be maintained when the misfire does not occur according to the EGR and HSG adjusting step. The exhaust reduction control method during the cold start is capable of improving exhaust gas purification efficiency.

Description

Control method for reducing emission gas during cold start {CONTROL METHOD FOR DECREASING EXHAUST GAS DURING COLD START}

The present invention relates to a control method for reducing exhaust gas during cold starting, and more particularly, by controlling the EGR opening rate and HSG filling amount of a hybrid vehicle to improve the purification performance of exhaust gas emitted when starting in a cold state. It relates to a control method for reducing city emissions.

In general, a hybrid vehicle is a combination of two or more driving sources, such as applying a motor of an electric vehicle to an existing internal combustion engine or using a combination of an internal combustion engine and a fuel cell. Many parts are recognized as improved cars.

Such a hybrid vehicle is designed in a way unique to each manufacturer, usually as shown in FIG. 1 , an engine 10 and a motor 12 arranged in series with each other, and an arrangement between the engine 10 and the motor 12 . An engine clutch 13 that transmits or cuts off engine power, an automatic transmission 14 that shifts and outputs a motor or motor and engine power to a traveling wheel, and an HSG ( 16, Hybrid Starter Generator), an inverter 18 for motor control and power generation control, an inverter to provide power to the motor 12, etc., and a high voltage battery 20 connected to charge and discharge. .

Meanwhile, as environmental issues have recently emerged as important issues, interest in a method for efficiently treating exhaust gases of automobiles is growing.

Even in the case of hybrid vehicles, catalysts are used to reduce exhaust gas of the engine when starting in a cold state, but since the catalyst activation temperature must be significantly higher than room temperature, the engine is activated to increase the catalyst temperature to activate it.

To this end, it is recommended to sufficiently retard the ignition angle in order to reduce kinetic energy and increase thermal energy among the energy generated by the engine. This may occur, and it is difficult to sufficiently delay the ignition angle because there is a disadvantage that it cannot be prepared quickly when the engine torque is required.

In particular, since the engine and the power output shaft are physically coupled, the vibration of the engine is easily transmitted to the driver, and the ignition angle is inevitably limited because it has a structure in which the driver's requested torque is output together with the engine.

As a result, in the cold state, it was difficult to shorten the catalyst activation time by increasing the exhaust temperature at the initial stage after starting.

An object of the present invention is to gradually increase the EGR opening rate and HSG filling amount for exhaust gas recirculation and fresh air inflow when starting in a cold state, and selectively increase the EGR opening rate and HSG filling amount depending on whether a misfire occurs in the engine By adjusting the EGR and HSG control with the EGR opening rate and HSG filling amount when misfire does not occur, the combustion stability of the catalyst heating area can be secured, and accordingly, the purification efficiency of the exhaust gas can be improved by the activated catalyst. It is to provide a control method for reducing exhaust gas during cold start.

The method for reducing exhaust gas during cold start according to the present invention is an EGR and HSG change step of gradually opening the EGR and increasing the HSG charge amount as a set time elapses after starting the engine in a cold state, the EGR and HSG change EGR and HSG control step of continuously adjusting the EGR opening rate and EGR filling amount when misfire occurs, and when misfire does not occur according to the EGR and HSG control step, corresponding It is characterized in that it comprises an EGR and HSG maintenance step of controlling the EGR opening rate and the HSG filling amount to be maintained.

The EGR and HSG change step gradually opens the EGR and increases the HSG charge amount within the maximum EGR usage and maximum HSG charge amount limits set until the time of occurrence of a misfire.

In the EGR and HSG adjustment step, when a misfire occurs according to the EGR and HSG adjustment step, the first step of stopping the opening of the EGR and selectively increasing the HSG filling amount, determining whether a misfire occurs according to the first step and, when a misfire occurs, the second step of gradually reducing the EGR opening rate and increasing the HSG filling amount and re-determining whether a misfire occurs according to the second step, and when a misfire occurs, the second and a third step of controlling the step to be repeated.

In addition, the first step causes the EGR and HSG maintenance steps to be performed when a misfire does not occur due to selectively increasing the HSG filling amount.

On the other hand, in the EGR and HSG change step, as the set time elapses, the catalyst measurement temperature and the set catalyst temperature are compared after the engine is started, and when the catalyst measurement temperature is lower than the set catalyst temperature, the HSG charge amount is increased. control

In addition, in the EGR and HSG adjustment step, the EGR usage is controlled by adjusting the engine ignition angle (ignition timing).

The present invention gradually increases the EGR opening rate and the HSG filling amount for exhaust gas recirculation and new inflow when starting in a cold state, and selectively adjusting the EGR opening rate and HSG filling amount depending on whether a misfire occurs in the engine. By controlling EGR and HSG by the EGR opening rate and HSG filling amount when misfire does not occur, it is possible to secure combustion stability in the catalyst heating region.

In addition, the present invention adjusts the load of the engine through HSG control, which can independently control only the engine independently of vehicle driving, to adjust the engine RPM and air amount to desired values, and to activate the catalyst quickly, at this time the EGR By recirculating the exhaust gas that has not been purified due to catalyst deactivation through control, the exhaust gas can be purified again by the more activated catalyst, thereby having the effect of improving the exhaust gas purification efficiency.

1 is a view showing a power transmission system diagram of a hybrid vehicle.
2 is a diagram schematically showing an engine system for a method for controlling emission gas reduction during cold start according to the present invention.
3 is a view sequentially showing a method for controlling emission gas reduction during cold start according to the present invention.

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

Advantages and features of the present invention, and a method for achieving the same, will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings.

However, the present invention is not limited by the embodiments disclosed below, but will be implemented in a variety of different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the art to which the present invention pertains It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims.

In addition, in the description of the present invention, when it is determined that related known techniques may obscure the gist of the present invention, a detailed description thereof will be omitted.

2 is a diagram schematically showing an engine system for a method for controlling emission gas reduction during a cold start according to the present invention, and FIG. 3 is a view sequentially showing a method for controlling emission gas reduction during a cold start according to the present invention.

In general, an exhaust gas recirculation device (hereinafter referred to as EGR) for reducing nitrogen oxide (NOx) sucks a part of the exhaust gas discharged after combustion and introduces it to the combustion chamber by including it in the mixer, thereby changing the air-fuel ratio of the mixer itself It has the characteristic of lowering the combustion temperature by lowering the density of the mixer.

That is, when the EGR device needs to reduce emissions such as NOx according to the operating state of the engine, a portion of the exhaust gas is provided to the intake intake through the EGR valve and introduced into the combustion chamber together with the mixer. The exhaust gas introduced into the furnace is an inert gas, and since the volume of the intake gas does not change, the density of the mixer is relatively lowered to lower the propagation speed of the flame, so the combustion rate is lowered, and accordingly, the combustion temperature is prevented from rising. It reduces the occurrence of emissions such as NOx.

An engine system including such an EGR may include an engine 20 , a turbocharger 70 , an intercooler 16 , and an EGR device, as generally illustrated in FIG. 2 .

The engine 20 includes a plurality of combustion chambers 21 that generate driving force by combustion of fuel, and the engine 20 includes an intake line 10 through which intake gas supplied to the combustion chamber 21 flows, and a combustion chamber ( An exhaust line 30 through which exhaust gas discharged from 21) flows is provided.

The exhaust line 30 is provided with an exhaust gas purification device 60 for purifying various harmful substances included in the exhaust gas discharged from the combustion chamber 21 .

The turbocharger 70 compresses intake gas (external air + recirculation gas) introduced through the intake line 10 and supplies it to the combustion chamber 21 . The turbocharger 70 is provided in the exhaust line 30, the turbine 71 rotates by the exhaust gas discharged from the combustion chamber 21, and a compressor that rotates in conjunction with the turbine 71 and compresses the intake gas ( 72).

The EGR device device includes a recirculation line 52 , an EGR cooler 56 , and an EGR valve 54 .

The recirculation line 52 is branched from the exhaust line 30 at the rear end of the turbocharger 70 and merges into the intake line 10 . The EGR cooler 56 is disposed in the recirculation line 52 , and cools the exhaust gas flowing through the recirculation line 52 . Here, the exhaust gas supplied to the intake line 10 through the recirculation line 52 is referred to as a recirculation gas.

On the other hand, a hybrid vehicle is a vehicle using two or more power sources, and generally refers to a hybrid electric vehicle driven using an engine and a motor. It may be formed in various structures.

As described above, since the hybrid vehicle is operated with two powers of the engine and the motor, only the engine can be operated independently in a region that does not require high power, so that the desired torque and RPM can be obtained separately from vehicle driving when the catalyst is heated using this. can keep

In particular, since it is possible to change the torque even at the same RPM through the charging torque control using the HSG (Hybrid Starter Generator), there is a great advantage in that the engine can be operated at the optimum point of the emission.

Using this, in this embodiment, the exhaust gas generated before the catalyst is activated is recirculated to the catalyst through the EGR opening, and thus the recycle gas is given an opportunity to be re-refined in a more activated catalyst, so that the exhaust gas can be reduced, and through the HSG charge control at this time, the amount of fresh air is adjusted by varying the engine load, thereby allowing complete combustion to occur, thereby effectively activating the catalyst.

In general, emission gas reduction devices such as EGR, LNT (Lean NOx Trap), and SCR (Selective Catalytic Reduction) do not operate normally due to the low operating coefficient of the reduction device at a low temperature of about 40 to 50˚C or less. It works to reduce nitrogen oxides (NOx), carbon monoxide (CO), and particulate matter (PM).

Therefore, in the cold state, when the engine temperature does not rise sufficiently after starting, if the HSG assists the engine torque, the engine room temperature rise rate is slowed down because the load that the engine bears is reduced, thereby emitting NOx, CO, PM, etc. Since the gas reduction performance is deteriorated, the engine room temperature can be increased by adjusting the engine load through the HSG charging control.

In order to achieve this goal, as shown in FIG. 3 , the method for controlling emission gas reduction during cold start according to the present embodiment will be sequentially described as follows.

First, after starting the engine in a cold state, when the set time elapses (S100), the EGR (Exhaust Gas Recirculation) is gradually opened, and the HSG (Hybrid Starter Generator) charging amount is also gradually increased together (S200).

That is, when the EGR is opened, since the EGR causes combustion instability, the deterioration of emissions such as NOx due to combustion instability is more pronounced when used in a cold state with a low cylinder temperature. It is common to use it mainly from the finished temperature.

However, since exhaust gas is generated from the start of the engine in a cold state, the exhaust gas generated when the engine is started in the cold state is recirculated after a set time by opening the EGR, and along with this, the new supply amount is increased by increasing the HSG charge amount. As a result, the exhaust gas can be re-purified from the activated catalyst.

In other words, after starting the engine in a cold state, the set time, for example, 5 seconds, is a time when the amount of air in the engine fluctuates a lot, so it is not suitable for using EGR for exhaust gas recirculation. It is gradually opened to allow the exhaust gas to be recirculated and to increase the HSG charge to improve combustion stability.

At this time, the HSG charge amount may be controlled to increase independently of the EGR opening, which is, as the set time elapses, the catalyst measurement temperature after engine start and the set catalyst temperature are compared, and if the catalyst measurement temperature is higher than the set catalyst temperature If low, the HSG charge can be individually controlled to increase to the set catalyst temperature.

This is because, when the control to increase the HSG charge amount is controlled, the engine load increases, and the catalyst measurement temperature also increases due to the improvement of the engine's combustibility. This is to be able to control the amount of HSG filling independently of use.

In this way, while the EGR is gradually opened and the HSG charge amount is also gradually increased, as a result of determining whether misfire occurs during incomplete combustion in the engine cylinder (S300), if it is determined that the misfire has not occurred, the EGR While gradually increasing the amount of exhaust gas for recirculation by gradually opening it, the amount of HSG filling is gradually increased until the misfire occurs so that the amount of incoming fresh air is also increased (S200).

Preferably, when misfire does not occur, in order to secure combustion stability of the catalyst heating region after starting the engine in a cold state, the EGR is gradually opened to reach the preset maximum EGR amount and maximum HSG charge amount until the misfire occurs, and the HSG charge amount More preferably, the maximum EGR usage and the maximum HSG filling amount may be set by mapping through a test according to the engine specification.

In addition, the method of determining whether a misfire occurs is, for example, by checking the engine speed to determine whether the range of change in which the engine speed rapidly decreases is larger than a preset reference value, and if it is determined that it is larger than the reference value, it is determined as a misfire and the method is applied can

More specifically, it is possible to calculate information corresponding to the number of revolutions based on the cycle for each predetermined crank angle corresponding to each cylinder of the engine, and detect the misfired state of the engine based on the change amount or rate of change of the information. This kind of misfire detection method is based on the fact that the torque of the crankshaft decreases and the rotational speed (angular velocity) of the crankshaft decreases when a misfire occurs in the cylinder. When the rate of change of speed is lower than the reference value, or when the rate of change of the engine rotation period sensed for each predetermined crankshaft rotation angle using the rotation period of the crankshaft exceeds the determination reference value, it may be determined that a misfire has occurred.

However, such a method of determining the misfire is only applicable to one embodiment and is not determined, and various methods for determining whether a misfire has occurred may be applied.

On the other hand, when it is determined that misfire has occurred as a result of determining whether misfire has occurred (S300), the EGR opening rate and HSG filling amount are continuously adjusted.

In other words, if a misfire occurs as the EGR opening rate and the HSG filling amount gradually increase, it means that incomplete combustion occurs in the engine cylinder due to the increase in EGR use. While the charging amount is continuously increased, the opening is stopped so that the amount of supplied EGR is the same as before (S400).

Thereafter, it is determined again whether a misfire occurs due to the increase in the HSG charge amount (S410), and when a misfire does not occur, complete combustion occurs in the engine and it is determined that exhaust gas can be reduced, so that the EGR opening rate and HSG charge amount are maintained. control (S500).

In addition, if it is determined again whether misfire has occurred due to the increase in the HSG filling amount (S410), when it is determined that the misfire has occurred, the EGR opening rate is gradually reduced while the HSG filling amount is increased (S420).

This is through the step (S410) of selectively increasing only the HSG charge amount, but whether misfire was determined, but still incomplete combustion occurred in the engine. By increasing the supply of fresh air, this is to cause complete combustion in the engine, and ultimately, to reduce exhaust gas and secure combustion stability in the catalyst heating area.

In addition, in order to reduce the EGR usage, it may be achieved by adjusting the ignition angle (ignition timing).

In other words, it is generally known that the ignition timing that produces the maximum output under the conditions of a specific engine speed and intake air amount is such that the maximum pressure due to combustion of the mixture occurs about 10 to 20 degrees before and after TDC.

As described above, the combustion speed at which the flame propagates inside the cylinder until the maximum pressure is reached depends on the operating state of the engine. Therefore, the ignition timing should be accelerated under the condition of a slow combustion speed, and conversely, the ignition timing should be increased when the combustion speed is high. should be delayed

Here, advancing the ignition timing is called advance, and slowing the ignition timing is called delay. Thus, it can be achieved by relatively increasing the inflow of fresh air compared to the amount of EGR used.

On the other hand, after the above-described step (S420), the EGR opening rate is gradually reduced, even though the HSG filling amount is increased. As a result of determining whether a misfire occurs (S430), when a misfire occurs, the EGR opening rate reduction and the HSG filling amount increase are controlled to repeat until the misfire does not occur.

And, if the misfire does not occur as a result of the determination of the misfire (S430), the EGR opening rate and the HSG charge amount are controlled to be maintained (S500).

Accordingly, by maintaining the corresponding EGR opening rate and HSG filling amount, the optimum EGR usage and HSG filling amount calculated through repeated misfire occurrences are controlled to ensure combustion stability in the catalyst heating area.

After all, in this embodiment, the exhaust gas generated after starting the engine in a cold state is recirculated through the EGR opening, and the combustion stability for the catalyst heating area is ensured by increasing the HSG charge amount to be recirculated and discharged after refining in an environment. By doing so, it is possible to effectively improve the exhaust gas purification efficiency even when the engine is started in a cold state.

The present invention gradually increases the EGR opening rate and the HSG filling amount for exhaust gas recirculation and new inflow when starting in a cold state, and selectively adjusting the EGR opening rate and HSG filling amount depending on whether a misfire occurs in the engine. By controlling EGR and HSG by the EGR opening rate and HSG filling amount when misfire does not occur, it is possible to secure combustion stability in the catalyst heating region.

In addition, the present invention adjusts the load of the engine through HSG control, which can independently control only the engine independently of vehicle driving, to adjust the engine RPM and air amount to desired values, and to activate the catalyst quickly, at this time the EGR By recirculating the exhaust gas that has not been purified due to catalyst deactivation through control, the exhaust gas can be purified again by the more activated catalyst, thereby having the effect of improving the exhaust gas purification efficiency.

Although the present invention has been described above with reference to the embodiment(s) shown in the drawings, this is only exemplary, and various modifications may be made therefrom by those skilled in the art, and the above-described embodiment It will be understood that all or part of (s) may optionally be combined. Accordingly, the true technical protection scope of the present invention should be defined by the technical spirit of the appended claims.

Claims (6)

After starting the engine in a cold state, as a set time elapses, the EGR and HSG change step of gradually opening the EGR and increasing the HSG charge amount together;
an EGR and HSG control step of performing the EGR and HSG change step, determining whether a misfire has occurred in the engine, and continuously adjusting the EGR opening rate and EGR filling amount when a misfire occurs; and
EGR and HSG maintenance step of controlling the EGR opening rate and HSG filling amount to be maintained when a misfire does not occur according to the EGR and HSG control step;
The method of claim 1,
The EGR and HSG change step is,
A control method for reducing exhaust gas during cold start, characterized in that the EGR is gradually opened within the limits of the maximum EGR usage and the maximum HSG filling amount set up to the time of the misfire, and the HSG filling amount is increased.
The method of claim 1,
The EGR and HSG control step,
a first step of stopping the opening of the EGR and selectively increasing the HSG filling amount when a misfire occurs according to the EGR and HSG control step;
a second step of determining whether misfire has occurred according to the first step, and when misfire occurs, gradually reducing the EGR opening rate and increasing the HSG filling amount; and
A third step of re-determining whether a misfire has occurred according to the second step, and controlling so that the second step is repeated until the misfire does not occur, when a misfire occurs; Way.
4. The method of claim 3,
The first step is
When a misfire does not occur by selectively increasing the HSG filling amount, the EGR and HSG maintenance step is performed.
The method of claim 1,
The EGR and HSG change step is,
As the set time elapses, the catalyst measurement temperature and the set catalyst temperature are compared after the engine is started, and when the catalyst measurement temperature is lower than the set catalyst temperature, the HSG charge amount is individually controlled to increase. Emission gas reduction control method.
The method of claim 1,
The EGR and HSG control step,
A control method for reducing exhaust gas during cold start, characterized in that the EGR usage is controlled by adjusting the engine ignition angle (ignition timing).

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