KR20080033641A - Method for controlling exhaust gas and catalyst temperature of internal combustion engine - Google Patents

Abstract

A method for controlling exhaust gas and catalyst temperature of an internal combustion engine is provided to lower the exhaust gas and catalyst temperature even without increasing fuel efficiency. A method for controlling exhaust gas and catalyst temperature of an internal combustion engine includes a step of collecting data for calculating the amount of residual gas, a step of calculating the amount of residual gas from the collected data, a step of calculating the exhaust gas and catalyst temperature by using the calculated amount of residual gas, and a step of comparing the exhaust gas and catalyst temperature with a preset temperature level, and controlling valve overlap if the exhaust gas and catalyst temperature is higher than the preset temperature level, such that the exhaust gas and catalyst temperature is maintained at the level lower than the preset temperature level.

Description

Method for controlling exhaust gas and catalyst temperature of internal combustion engine

1 is a view showing a driving state of the HWFET mode,

2 is a graph illustrating valve overlap between an intake valve and an exhaust valve;

3 is a view showing an operating region according to a valve overlap;

4 is a diagram showing a composition ratio according to an RGF value,

5 and 6 are views showing the trend of the exhaust gas temperature and the catalyst temperature according to the valve adjustment time,

7 is a graph showing the exhaust system temperature according to the intake valve opening value IVO;

8 is a graph showing an exhaust system temperature different from the residual gas amount RGF;

9 is a flow chart showing another exhaust system temperature control process in the present invention.

The present invention relates to a method for controlling the temperature of the exhaust system of an internal combustion engine, and more particularly, calculates the temperature of the catalyst and the exhaust gas using the residual gas amount, and increases the residual gas amount by adjusting the valve overlap when these temperatures are above a certain temperature. The present invention relates to a method for controlling the temperature of an exhaust system of an internal combustion engine so that the temperature of the exhaust system can be appropriately lowered.

Today's automotive market has changed to a harsh reality that threatens to survive as an automaker if it fails to meet ever-increasing emissions regulations for the protection of consumers' preferences for high power and low fuel consumption and the protection of the atmosphere.

In particular, the goal of developing high-power and low-fuel engines has been a challenge that engine development engineers have pursued since the beginning of the automotive industry.In the case of gasoline engines, the representative technology currently proposed as the answer is gasoline direct injection (CDI). ) And variable valve timing system (VVT).

The variable valve timing system is divided into 2 points or continuous systems according to the operating point, and is divided into dual types that can control both the intake valve, the exhaust valve, and the intake / exhaust valve according to the valve whose opening / closing time is adjusted.

Among these, Continuous Variable Valve Timing (CVVT) continuously adjusts the opening and closing timing of the valve according to the engine's operating condition to improve engine output, reduce harmful components of exhaust gas, and improve fuel efficiency. .

On the other hand, recently, the fuel efficiency improvement of vehicles due to high oil prices has become a hot topic, and one of the major factors in the fuel efficiency problem of the actual vehicle is the fuel efficiency problem at the time of high speed driving.

Under normal driving conditions, high-speed, high-load driving patterns such as overpasses and overtakings appear. On the contrary, in order to protect the exhaust manifold for durability, the engine is controlled more richly outside the condition of Lambda = 1.

The durability problem of the exhaust manifold is related to the temperature of the exhaust gas, and a method of lowering the temperature of the exhaust gas is used for durability protection.

In addition, excessively high exhaust gas temperature causes catalyst damage, such as melting of expensive precious metals contained in the catalyst.

In the related art, the temperature reduction of the exhaust gas is a method of lowering the temperature of the combustion gas by simply injecting more fuel and using a large specific heat of the fuel component.

This method is widely used because it not only reduces exhaust temperature but also benefits power performance at high speed.

However, there is a problem of high-speed fuel economy due to excessive fuel injection, and as the fuel economy becomes important recently, the high-speed fuel economy problem has emerged as a bigger problem.

In addition, for safety, some applications are applied in the heavy load area, causing unnecessary fuel consumption and excessive emission of exhaust gas.

Accordingly, researches such as material change of the exhaust manifold have been actively conducted, but this also has a limitation, and therefore, an engine control technique for reducing the temperature of the exhaust system using a continuously variable valve timing system (CVVT) is required.

Therefore, the present invention is invented to solve the above problems, by using the residual gas amount to calculate the temperature of the catalyst and exhaust gas, and by increasing the residual gas amount by adjusting the valve overlap when these temperatures are above a certain temperature It is an object of the present invention to provide a method for controlling the temperature of an exhaust system of an internal combustion engine that can appropriately lower the temperature of the exhaust system without increasing fuel economy and prevent excessive temperature rise of the exhaust system.

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

In order to achieve the above object, the present invention includes the steps of collecting data for calculating the residual gas amount;

Calculating a residual gas amount using the collected data;

Calculating a temperature of the exhaust system using the calculated residual gas amount;

Controlling the temperature of the exhaust system to be below a predetermined level by adjusting a valve overlap when the temperature of the exhaust system is compared with a preset reference temperature;

It provides a method for controlling the exhaust system temperature of the internal combustion engine comprising a.

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

The present invention uses a continuously variable valve timing system (CVVT) to prevent the exhaust system temperature from excessively rising, using the residual gas amount to calculate the temperature of the catalyst and the exhaust gas, if the temperature is above a certain temperature valve By adjusting the overlap, the amount of residual gas is increased, thereby reducing the exhaust gas and reducing the temperature of the exhaust system.

Hereinafter, a theoretical related technique will be described first before describing the present invention of adjusting the valve overlap for reducing the exhaust system temperature in an engine to which a continuously variable valve timing system is applied.

Immediately after the intake valve closing (IVC), the load in the cylinder consists of a mixture of fuel, air and residual gas.Residual Gas Fraction (RGF) is defined using a mass fraction. If this is expressed using load, it is as follows.

here,

RGF: residual gas amount,

M _RG : mass of residual gas,

M _A : mass of fresh air,

M _F : mass of fuel,

rfr: relative filling via internal and external EGR,

rl: relative filling of fresh air.

At this time, the actual measurement of the residual gas amount is calculated through the amount of CO ₂ respectively measured in the intake manifold, the exhaust manifold, and the cylinder.

On the other hand, the inventors of the present invention target the engine (DOHC 1600cc) equipped with a continuously variable valve timing system in order to determine the operating range according to the valve adjustment time, the RGF according to the valve adjustment time, the exhaust system temperature trend according to the valve adjustment time. The study was conducted.

In this study, a vane type intake valve variable continuous variable valve timing system of Denso, Japan was used. The test methods and conditions are as follows.

1) Fuel used: RON87

2) Test vehicle: 1600cc displacement, 2500 miles ODO

3) Test temperature: 24 ~ 25 ℃

4) Test mode: North American standard HWFET mode (driving distance: 10.25 miles, driving time: 765 seconds, maximum vehicle speed: 59.9 MPH, average vehicle speed: 48.1 MPH)

5) Test method: While driving the intake valve opening value (IVO: Intake Valve Open) in the HWFET mode of Fig. 1, keep it constant.

6) Valve Overlap: When driving the HWFET mode, the valve adjustment timing is determined by fixing the opening of the exhaust valve and then adjusting the opening of the intake valve to determine the valve overlap. At this time, the values for the reference portion of the intake valve and the exhaust valve were set as shown in Table 1 below based on TDC (Top Dead Center), and the valve lift was 1.0 mm when the intake valve was adjusted. Adjusted. 2 is a graph showing the valve overlap between the intake valve and the exhaust valve. The valve overlap is adjusted by fixing the opening of the exhaust valve and adjusting the opening of the intake valve. At this time, by adjusting the intake valve is adjusted to the maximum valve overlap (Mid Valve Overlap), and the minimum valve overlap (Min Valve Overlap). As shown in FIG. 2, the maximum valve overlap value by adjusting the intake valve is 42, the intermediate valve overlap is 22, and the minimum valve overlap is 2.

As a result of the test, first, the operation area according to the valve adjustment time will be described. FIG. 3 is a view showing the operation area according to the valve overlap, and the operation area according to each valve adjustment time is displayed together with the engine speed and the load. In addition, the frequency of the operation area is indicated in the form of contour line.

In FIG. 3, when more than 1% of driving was performed in the corresponding area while driving in the premise mode.

As shown in FIG. 3, the operating ranges are similar for each valve overlap as a whole, but the operating ranges in the engine rotational speed of 2000 to 2400 RPM and the load of 25 to 65%, which correspond to most operating regions, are compared in Table 2. Doing.

In all three cases of overlap, the operating area corresponds to about 78% of the total area under the above conditions, and the detail tends to be similar, which is suitable for analyzing the residual gas amount (RGF) in the same operating area.

Referring to the residual gas amount (RGF) according to the next valve adjustment time, it can be seen that the trend of RGF increases as the valve overlap increases in Figure 4 and Table 2.

At three different valve overlaps, RGF = 2.5 or higher rarely occurs during HWFET mode operation, and is distinguished between RGF = 0 and 1.0.

In the case of maximum valve overlap, the part corresponding to RGF = 1.0 is dominant (approximately 80% when driving in mode), and in the middle valve overlap, parts corresponding to RGF = 0.5 and 1.0 show about 40% and 50%, respectively. In the minimum valve overlap, the area corresponding to RGF = 0.5 is dominant, about 80% of the total.

As a result, it can be confirmed that as the overlap is increased by opening the intake valves, the generation by the reverse flow, which is one of the residual gas generating mechanisms, is dominant.

In addition, the RGF, which is a measure of the size of the residual gas, has almost no value above 2.5, which means that there is a limit to increase the RGF only by adjusting the intake valve.

Next, the trend of the exhaust system temperature according to the valve adjustment timing will be described. The trend of the exhaust system temperature, that is, the exhaust gas temperature and the catalyst temperature, according to the valve adjustment timing is as shown in FIGS. 5 and 6.

When the intake valve is most advanced and the valve overlap is maximized, the value of the RGF becomes the maximum value, and the exhaust gas temperature has the minimum value.

5 and 6, by varying the RGF, the temperature conditions in the laboratory are kept the same during the test, and the cooling water temperature behavior of the vehicle and the behavior of the cooling fan during the same HWFET mode are tested under the same conditions. The best test conditions were constructed so that only trends by RGF were considered.

As can be seen in Figure 6, as the RGF has a different value, the exhaust gas temperature and the catalyst temperature has a difference of up to about 30 degrees, the average exhaust gas temperature is 13 ℃ than the maximum RGF day versus the minimum RGF The catalyst temperature decreases by about 20 ° C.

In the case of the catalyst, the temperature of the catalyst, i.e., the specific heat of the carrier is larger than that of the air, is shown to have a greater effect of reducing the temperature.

-Maximum RGF (Maximum Valve Overlap) Exhaust Gas Average Temperature: 554 ℃

-Maximum RGF (Maximum Valve Overlap) Catalyst Average Temperature: 624 ℃

-Minimum RGF (Minimum Valve Overlap) Exhaust Gas Average Temperature: 567 ℃

Minimum RGF (minimum valve overlap) Catalyst Average Temperature: 644 ℃

FIG. 7 is a graph showing the exhaust system temperature according to the intake valve opening value IVO, and FIG. 8 is a graph showing the exhaust system temperature different from the residual gas amount RGF.

As shown in the figure, it can be seen that the exhaust system temperature (exhaust gas and catalyst temperature) is lowered as the valve overlap and the residual gas amount are larger.

First, in FIG. 7, the correlation between the IVO and the exhaust system temperature may be expressed by the following equation using a linear approximation.

Catalyst Temperature (° C) = 638 + 0.998 × IVO

Exhaust gas temperature (℃) = 558.55 + 0.325 × IVO

Where IVO is the opening value of the intake valve.

In addition, in FIG. 8, the correlation between the RGF and the exhaust system temperature may be expressed by the following equation using a linear approximation.

Catalyst temperature (° C) = C _a + C _b × RGF = 722-89.89 × RGF

Exhaust gas temperature (℃) = C _c + C _d × RGF = 585.87-29.2 × RGF

Where RGF is the residual gas amount.

In addition, the relation between RGF and IVO can be obtained from Equations 2 and 3 as shown in Equation 4 below.

Catalyst temperature: RGF (= RGF _cat ) = C ₁ + C ₂ × IVO = 0.934475-0.011102 × IVO

Exhaust gas temperature: RGF (= RGF _exh ) = C ₃ + C ₄ × IVO = 0.935296-0.011126 × IVO

As a result, each of the coefficients in the equations (2), (3) and (4) is obtained from the test, and the values of the coefficients in the equation (4) have similar values, which are different from the exhaust gas temperatures of the air and the catalyst carrier having different specific heats. It shows high reliability of RGF and IVO induced at catalyst temperature.

On the other hand, the inventor proposes a method for preventing excessive rise in exhaust system temperature based on the above research results, which will be described step by step as follows.

9 is a flowchart illustrating another exhaust system temperature control process according to the present invention.

CVVT OCV (Oil Control Valve), Intake Temperature Sensor, Water Temperature Sensor (10 ~ 100 ℃), etc. are checked for normal operation and after a certain time (eg 10 ~ 60sec) has elapsed. (S1), data for calculating the residual gas amount (RGF) value is collected (S2).

At this time, the collected data are the current exhaust gas ratio rfr, the air ratio rl, and the intake valve opening values, which are data already used for engine control.

Then, using the collected data, the first residual gas amount RGF ₁ calculated as in Equation 1, and the residual gas amounts RGF _cat and RGF _exh for the catalyst temperature and the exhaust gas temperature calculated as in Equation 4 ) Are respectively calculated (S3, S4).

In calculating the residual gas amount for the catalyst temperature and the exhaust gas temperature by Equation 4, each coefficient C ₁ , C ₂ , C ₃ , C ₄ is a coefficient value obtained from the experiment, C ₁ = 0.934475, C ₂ = 0.011102 , C ₃ = 0.935296, C ₄ = 0.011126.

As in Equation 4, the residual gas amount for the catalyst temperature and the exhaust gas temperature is determined by the calculation of the coefficient value determined by the experimental data and the intake valve opening value, and the coefficient value determined by the experimental data is shown in FIGS. It is computed by the experiment and result demonstrated with reference to FIG.

Next, a higher gas residual amount is obtained by comparing the first residual gas amount calculated by the theoretical formula as described above with the residual gas amount with respect to the catalyst temperature and the exhaust gas temperature calculated by the experimentally obtained linear formula (S5). The temperature of the catalyst and the temperature of the exhaust gas calculated by Equation 3 are calculated using the gas residual amount taken here (S6).

In calculating the catalyst temperature and the exhaust gas temperature by Equation 3, the coefficients C _a , C _b , C _c , and C _d are coefficient values obtained from the experiment, and C _a = 722, C _b = -89.89, C _c = 585.87, C ₄ = -29.21.

As in Equation 3, the catalyst temperature and the exhaust gas temperature are determined by the calculation of the coefficient value and the residual gas amount determined by the experimental data, the coefficient value determined by the experimental data is described in the experiment and It is calculated by the result.

Thereafter, when the calculated exhaust system temperature is compared with the reference temperature (S7) or more than the reference temperature, the valve overlap is adjusted (S8). At this time, the opening of the exhaust valve is fixed and the opening of the intake valve is adjusted as shown in FIG. To adjust the valve overlap (adjusting the opening value of the intake valve).

The reference temperature value is a value set dependently on the vehicle state such as the coolant temperature and the intake temperature, and the valve overlap is adjusted when any of the exhaust gas temperature and the catalyst temperature is higher than the reference temperature.

When the valve overlap is adjusted, the current intake valve opening value IVO is adjusted to reflect the change amount ΔIVO of the intake valve opening value, and the change amount of the intake valve opening value is preset according to the coolant temperature and the intake temperature. In order to lower the temperature of the exhaust system, the opening value of the intake valve is adjusted to reflect the set value, thereby advancing the valve timing of the intake valve and increasing the valve overlap.

In this way, the present inventors confirmed that the residual gas amount (RGF) increased as the valve overlap increased by fixing the exhaust valve and adjusting the opening (IVO) timing of the intake valve. It was confirmed that it is an important factor, and the method of reducing the exhaust system temperature by adjusting the intake valve opening value by analyzing the tendency of the exhaust system temperature with increasing residual gas amount was suggested.

Therefore, according to the present invention as described above, by using the residual gas amount to calculate the temperature of the catalyst and exhaust gas, and when these temperatures are above a certain temperature, by adjusting the valve overlap to increase the residual gas amount, the effect of reducing the exhaust gas In addition, the effect of reducing the temperature of the exhaust system can be obtained.

As described above, according to the method for controlling the temperature of the exhaust system of the internal combustion engine according to the present invention, the temperature of the catalyst and the exhaust gas is calculated using the residual gas amount, and when the temperature is above a certain temperature, the valve overlap is adjusted to adjust the residual gas amount. By increasing, it is possible to obtain the effect of reducing the temperature of the exhaust system as well as the effect of reducing the exhaust gas.

As a result, problems such as durability of the exhaust manifold or catalyst damage caused by excessive exhaust system temperature rise can be solved by applying logic only according to the present invention without any additional hardware. The effect can be reduced.

As described above, in order to lower the temperature of the exhaust system, fuel consumption and exhaust gas increase problems may be solved by increasing the fuel injection amount.

Claims (9)

Collecting data for calculating a residual gas amount; Calculating a residual gas amount using the collected data; Calculating a temperature of the exhaust system using the calculated residual gas amount; Controlling the temperature of the exhaust system to be below a predetermined level by adjusting a valve overlap when the temperature of the exhaust system is compared with a preset reference temperature; Exhaust system temperature control method of an internal combustion engine comprising a. The method according to claim 1, The temperature of the exhaust system is the first residual gas amount calculated using the ratio of the exhaust gas and the air ratio, and the residual gas amount with respect to the catalyst temperature calculated using the opening value of the intake valve, and the residual gas residual temperature. An exhaust system temperature control method for an internal combustion engine, characterized in that the calculation is performed using a large amount of residual gas in the gas amount. The method according to claim 2, The first residual gas amount is determined by the following equation, the exhaust system temperature control method of the internal combustion engine. RGF ₁ = rfr / {rfr + rl × (14.1 + 1)} Here, RGF ₁ is the first residual gas amount, rfr is the ratio of the exhaust gas, rl is the ratio of air. The method according to claim 2, A method of controlling the exhaust system temperature of an internal combustion engine, wherein the amount of residual gas with respect to the catalyst temperature is determined by the following equation. RGF _cat = 0.934475-0.011102 × IVO Where RGF _cat is the residual gas volume with respect to the catalyst temperature and IVO is the opening value of the intake valve. The method according to claim 2, The amount of residual gas with respect to the exhaust gas temperature is determined by the following equation. RGF _exh = 0.935296-0.011126 × IVO Here, RGF _exh is the residual gas amount with respect to the exhaust gas temperature, IVO is the opening value of the intake valve. The method according to claim 1, The temperature of the catalyst and the temperature of the exhaust gas are calculated using the residual gas amount, and if the temperature of the catalyst and the temperature of the exhaust gas is higher than a reference temperature, the valve overlap of the internal combustion engine is increased. Control method. The method according to claim 1 or 6, The valve overlap is a knocking control method of the internal combustion engine, characterized in that for controlling the opening of the exhaust valve by adjusting the opening of the intake valve. The method according to claim 7, The temperature (° C.) of the catalyst is determined by the following equation, the exhaust system temperature control method of the internal combustion engine. Catalyst Temperature = 722-89.89 × RGF Where RGF is the residual gas amount. The method according to claim 7, The exhaust gas temperature control method of an internal combustion engine, characterized in that the temperature (° C.) of the exhaust gas is determined by the following equation. Exhaust gas temperature = 585.87-29.2 × RGF Where RGF is the residual gas amount.

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