KR102575419B1 - Control method for ensuring exhaust purification efficiency of engine system - Google Patents

Abstract

The present invention relates to a control method for securing exhaust purification efficiency of an engine system, and more particularly, by supplying cooling air between a diesel particulate filter (DPF) and a nitrogen oxide reduction device (SCR) under a regeneration condition of the SCR. An object of the present invention is to provide a control method for ensuring exhaust purification efficiency of an engine system capable of optimizing the exhaust purification efficiency of the SCR without increasing the amount of urea injection by controlling the inlet gas temperature and maintaining it within an appropriate range.

Description

Control method for ensuring exhaust purification efficiency of engine system}

The present invention relates to a control method for securing the exhaust purification efficiency of an engine system, and more particularly, to prevent the exhaust purification efficiency of a nitrogen oxide reduction device (SCR) from being reduced under regeneration conditions of a diesel particulate filter (DPF). It relates to a control method for securing exhaust purification efficiency of an engine system.

In general, in the case of a diesel engine, an engine system using a turbocharger for intake supercharging or simultaneously using a turbocharger and a supercharger is applied. The turbocharger compresses air introduced into the engine intake line by rotating a compressor on the engine intake line using a turbine rotated by exhaust gas generated when the engine is driven, so that the supercharger is charged to the engine combustion chamber. The compressor on the intake line of the engine is rotated using the power of the motor or the engine to compress the air introduced into the intake line of the engine so that it is supercharged to the combustion chamber of the engine.

On the other hand, a diesel particulate filter (DPF) for removing particulate matter (PM) in exhaust gas and nitrogen oxides for removing nitrogen oxides (NOx) in exhaust gas are installed on the turbine outlet side of the turbocharger. A reduction device (SCR, Selective Catalytic Reduction) is being installed.

In the case of the diesel particulate filter (DPF), regeneration is performed by burning and removing particulate matter accumulated in the filter (DPF) by a temperature rise using exhaust heat of the engine. Therefore, in the DPF regeneration condition of the diesel engine, high-temperature exhaust gas (about 550 to 650° C.) flows into the nitrogen oxide reduction device (SCR).

Normally, the optimal exhaust purification efficiency of SCR is formed at the level of 300~350℃, and in the case of urea injected at the inlet side of SCR by the urea injector, an oxidation reaction occurs when the temperature exceeds 350℃, Compared to the amount (amount of urea injected), the amount that can be used in SCR (amount of urea used) decreases.

In this situation, a problem arises in that the exhaust purification efficiency of the SCR is lowered, and when the urea usage amount is restored to the original level in order to prevent the efficiency deterioration, the urea injection amount has to be increased.

Patent Publication No. 10-2009-0012430 Registered Patent No. 10-1714265

The present invention has been devised in consideration of the above points, and in the regeneration condition of the diesel particulate filter (DPF), cooling air is supplied between the DPF and the nitrogen oxide reduction device (SCR) to control the temperature of the gas at the inlet of the SCR by reducing the temperature An object of the present invention is to provide a control method for ensuring the exhaust purification efficiency of an engine system capable of optimizing the exhaust purification efficiency of the SCR without increasing the urea injection amount by maintaining it within an appropriate range.

Accordingly, in the present invention, the regeneration determination step of determining whether to regenerate the diesel particulate filter (DPF) installed in the engine exhaust line; When the DPF is regenerated, a temperature control step of controlling the inlet gas temperature of the nitrogen oxide reduction device (SCR) disposed at the outlet side of the DPF within a target temperature range set to ensure exhaust purification efficiency of the SCR; It provides a control method for securing exhaust purification efficiency of an engine system, characterized in that it comprises a.

According to an embodiment of the present invention, in the temperature control step, the supply flow rate of cooling air supplied between the DPF and the SCR to reduce the temperature of the gas at the inlet of the SCR ( ) A first step of calculating; and a second step of controlling the number of revolutions of a motor of an electric supercharger for pressurizing the cooling air between the DPF and the SCR.

In the first step, the gas flow rate passing through the DPF ( ), the DPF outlet gas temperature (T _{DPF_out} ), the SCR inlet gas target temperature (T _{SCR_in_target} ), and the cooling air supply flow rate (T _cool ) based on ) is calculated, and specifically, the supply flow rate of the cooling air ( )silver

is calculated by

In addition, in the second step, the DPF outlet pressure (P _{DPF_out} ) and the supply flow rate of cooling air ( Determining a supply pressure (P _cool ) of the cooling air as a pressure value higher than a predetermined value or more than a DPF outlet pressure (P _{DPF_out} ) based on ); The engine intake flow rate and the supply flow rate of the cooling air ( ) determining a boost pressure (P _boost ) of engine intake supplied to the electric supercharger side based on the sum of the flow rates; Determining a motor rotational speed of the electric supercharger based on a pressure ratio (γ _eBooster ) between the cooling air supply pressure (P _cool ) and the boost pressure (P _boost ) and the cooling air supply pressure (P _cool ) includes; At this time, the pressure ratio (γ _eBooster ) is

에 의해 계산되며,

is calculated by

The motor rotational speed of the electric supercharger is determined by a motor rotational speed model configured to determine the motor rotational speed based on the pressure ratio (γ _eBooster ) and the cooling air supply pressure (P _cool ).

According to the control method of an engine system according to the present invention, when a diesel particulate filter (DPF) is regenerated, nitrogen oxides are reduced due to an exhaust temperature rise for DPF regeneration by controlling the temperature of the inlet gas temperature of a nitrogen oxide reduction device (SCR). It is possible to prevent the exhaust purification efficiency of the device (SCR) from being reduced and to ensure optimal efficiency, and also to prevent the reduction of the amount of urea used in the SCR by preventing the oxidation of urea injected at the inlet side of the SCR under DPF regeneration conditions. As a result, there is an advantage of optimizing the amount of urea injected at the inlet side of the SCR.

1 is a configuration diagram showing an engine system according to the present invention
2 is a diagram showing a gas flow when a diesel particulate filter (DPF) of an engine system according to the present invention is not regenerated.
3 is a diagram showing gas flow during regeneration of a diesel particulate filter (DPF) of an engine system according to the present invention;
Figure 4 is a schematic diagram showing a control method for securing the exhaust purification efficiency of the engine system according to the present invention
5 is a diagram showing gas flow during regeneration of a diesel particulate filter (DPF) of a conventional engine system.

Hereinafter, the present invention will be described so that those skilled in the art can easily practice it.

According to the present invention, an engine system for maintaining exhaust purification efficiency of a nitrogen oxide reduction device (SCR) at an optimum level even under a regeneration condition of a diesel particulate filter (DPF) may be configured as shown in FIG. 1 .

As shown in FIG. 1, the engine system includes a turbocharger 110 for supercharging intake air supplied to the engine 100 and an electric supercharger 120, and the intake line of the engine 100 An air cleaner 130 and an intercooler 134 are installed in the (intake passage), and a diesel particulate filter (DPF) 140 and a nitrogen oxide reduction device (SCR) are installed in the exhaust line (exhaust passage) of the engine 100. (142) and the like are installed.

The air cleaner 130 removes foreign substances from air introduced into the intake line, and may be disposed at a front end of the LP-EGR valve 132 based on a gas flow direction.

The intercooler 134 cools the air (intake) heated by compression of the turbo charger 110 and supplies it to the combustion chamber of the engine 100, and is located at the rear end of the compressor 114 of the turbo charger based on the gas flow direction. can be placed.

The diesel particulate filter (DPF) 140 removes particulate matter included in the exhaust gas discharged from the engine 100 and may be disposed at the rear end (outlet side) of the turbine 112 of the turbo charger 110. .

The nitrogen oxide reduction device (SCR) 142 purifies and removes nitrogen oxides contained in the exhaust gas, and may be disposed at the rear end (outlet side) of the DPF 140.

The turbocharger 110 is configured by coaxially connecting a turbine 112 installed in the exhaust line of the engine 100 and a compressor 114 installed in the intake line of the engine 100, and when the engine 100 is running It is configured to rotate the compressor 114 using the turbine 112 rotated by the generated exhaust gas, and the air (intake) supplied to the engine intake line is compressed by the rotation of the compressor 114. Allow the engine to be supercharged into the combustion chamber.

The electric supercharger 120 is configured to rotate the compressor 122 installed in the engine intake line by using the power of the motor 124, and the air in the engine intake line is compressed by the rotation of the compressor 122. to force the engine into the combustion chamber.

Between the intercooler 134 and the compressor 122 of the supercharger, intake air passing through the intercooler 134 bypasses (bypasses) the compressor 122 of the supercharger and is supplied to the engine combustion chamber. 136 is configured, and a bypass valve 138 for opening and closing the passage is installed in the bypass passage 136. The bypass valve 138 is operated to close the flow path when the supercharger 120 is operated and to open the flow path when the supercharger 120 is not operated. Accordingly, intake air passing through the intercooler 134 is supplied to the engine 100 through the compressor 122 of the supercharger when the supercharger 120 is operating, and when the supercharger 120 is not operating, the intake air is supplied to the engine 100. It passes through the bypass flow path 136 and is supplied to the engine 100 (see FIG. 2).

In addition, between the rear end of the DPF 140 and the rear end of the air cleaner 130, the exhaust gas purified by the DPF 140 is supplied to the rear end of the air cleaner 130 (ie, the front end of the turbo charger compressor). An LP-EGR flow path 144 for cooling the exhaust gas purified by the DPF 140 may be installed in the LP-EGR flow path 144 .

In addition, between the rear end of the compressor 122 for the supercharger and the LP-EGR passage 144, cooling air for supplying the intake air compressed by the compressor 122 for the supercharger to the LP-EGR passage 144 The flow path 148 is configured to extend. The cooling air passage 148 may be disposed to be connected to the front side of the LP-EGR cooler 146, and the cooling air passing through the cooling air passage 148 passes through the LP-EGR cooler 146 in the reverse direction. and supplied to the outlet side of the DPF 140 (ie, the rear end of the DPF).

A flow control valve 150 for controlling air flow is installed at the rear end (ie, outlet side) of the compressor 122 for the supercharger, and the flow control valve 150 is operated by the compressor 122 for the supercharger. It may be controllably configured to supply compressed air to one of the cooling air passage 148 and the intake manifold inlet passage 154, and may be configured as a three-way valve, for example. A throttle valve 156 may be installed in the intake manifold inlet passage 154 to open and close the passage.

The DPF 140 repeats the process of collecting, removing, and collecting particulate matter contained in the exhaust gas again. is played

Referring to FIG. 5 , the conventional engine system reduces the intake air flow rate of the engine 100 by opening a vane (not shown) configured together with the turbine 112 of the turbo charger when the DPF 140 is regenerated. (reduction of boost pressure) and the HP-EGR valve 158 is closed to stabilize the combustion of the engine 100. The HP-EGR valve 158 is an opening/closing means installed in the HP-EGR flow path 162 formed between the exhaust manifold 160 and the intake manifold 152, and the turbocharger 110 rotates the shaft of the vane. It is possible to adjust the momentum transmitted to the blades of the turbine 112 by adjusting the flow angle of the exhaust gas. In addition, the fuel injection system of the engine 100 is controlled to increase post-injection, thereby increasing the temperature of the exhaust gas. At this time, the exhaust temperature (exhaust gas temperature at the rear end of the DPF) passing through the DPF 140 may rise to about 550 to 650°C. The post-injection is a fuel injection that is generated to increase the exhaust temperature after the main injection to secure the output of the engine 100 .

That is, in the regeneration condition of the DPF 140, the temperature of the exhaust gas is higher than in normal times when the DPF 140 is not regenerated, and the high-temperature exhaust gas (about 550 to 650 ° C) is After passing through, it flows into the SCR (142). The exhaust purification efficiency of the SCR (142) is optimized at a temperature (approximately 300 to 350 ° C) lower than a certain value than the exhaust gas temperature during DPF (140) regeneration. In the case of urea injected on the side, an oxidation reaction occurs when the temperature exceeds 350 ° C, so the amount that can be used in the SCR (urea consumption) is reduced compared to the amount actually injected from the urea injector 164 (urea injection amount). In this situation, a problem arises in that the exhaust purification efficiency of the SCR 142 decreases, and when the amount of urea used is restored to the original level in order to prevent the decrease in efficiency, a problem arises in that the amount of urea injection must be increased.

Therefore, in the present invention, cooling air is supplied between the DPF (140) and the SCR (142) under the regeneration condition of the DPF (140) to maintain the temperature at the inlet side of the SCR (142) within a range that can secure the optimal purification efficiency of the SCR (142). By doing so, it is possible to prevent a decrease in purification efficiency of the SCR 142 without increasing the amount of urea injection.

Hereinafter, a system control method for ensuring optimal purification efficiency of the SCR 142 without increasing the amount of urea injected during regeneration of the DPF 140 in the engine system configured as shown in FIG. 1 will be described.

2 is a diagram showing gas flow when the DPF is not regenerated, and FIG. 3 is a diagram showing the gas flow when the DPF is regenerated.

As shown in FIG. 2, the air compressed by the compressor 114 of the turbo charger 110 in the non-regenerated condition of the DPF 140 passes through the intercooler 134 and then passes through the bypass valve 138 and the supercharger. It passes through any one of the compressors 122 and is supplied to the engine combustion chamber. The air compressed by the compressor 114 of the turbocharger 110 passes through the compressor 122 for the supercharger and is supplied to the engine combustion chamber when the compressor 122 for the supercharger is operated. When the compressor 122 is not operating, it passes through the bypass valve 138 and is supplied to the engine combustion chamber.

And, as shown in FIG. 3, in the regeneration condition of the DPF 140, the air compressed by the compressor 114 of the turbocharger passes through the intercooler 134 and then diverges to the bypass valve 138 and the supercharger. It passes through the compressor 122 simultaneously/both. The air (combustion air) passing through the bypass valve 138 is supplied to the engine combustion chamber, and the air (cooling air) passing through the compressor 122 of the supercharger is supplied to the LP-EGR by the flow control valve 150. It passes through the flow path 144 and is pumped to the flow path connected between the DPF 140 and the SCR 142. The cooling air is for reducing the temperature of the exhaust gas heated up for regeneration of the DPF 140, and is supplied to the LP-EGR flow path 144 by using the electric supercharger 120 as a pump for pumping, and the LP-EGR It passes through the flow path 144 in the reverse direction and is supplied to the outlet side of the DPF 140 and the inlet side of the SCR 142.

The supply flow rate and supply pressure of the cooling air are controlled to reduce the temperature of the exhaust gas passing between the DPF 140 and the SCR 142 to a set target temperature range, and the supply flow rate and supply pressure of the cooling air are The decision is controlled by a controller (not shown). In this case, the controller may be an engine controller in charge of overall control of the engine system.

To control the supply of the cooling air, the controller first determines whether the DPF 140 is regenerated as shown in FIG. 4 . When it is determined that the temperature of the exhaust gas passing through the DPF (140) corresponds to the regeneration temperature range (eg, 550 to 650 ° C) of the DPF (140), the controller enters the DPF (140) into the regeneration mode It is determined that regeneration of the DPF 140 is being performed. If the temperature of the exhaust gas passing through the DPF 140 is not included in the regeneration temperature range of the DPF 140, the controller determines that the DPF 140 has not entered the regeneration mode.

When the DPF 140 enters the regeneration mode and the DPF 140 is regenerated, the controller adjusts the gas temperature at the inlet side of the SCR 142 disposed at the outlet side of the DPF 140 to set the exhaust purification efficiency to the optimum range. Control the temperature to be included in the set target temperature range (eg, 300 ~ 350 ℃) to secure within. The target temperature range may be changed depending on the vehicle.

In order to reduce the temperature of the inlet gas of the SCR 142 to the target temperature range, the controller first sets the DPF outlet gas temperature T _{DPF_out} , the SCR inlet gas target temperature T _{SCR_in_target} , and the DPF 140 It is determined by estimating the temperature (T _cool ) of the cooling air supplied between the SCR (142). The DPF outlet gas temperature T _{DPF_out} can be estimated using a DPF outlet gas temperature model previously built through experiments and evaluations. It may be configured as a model capable of predicting and determining the gas temperature at the outlet side of the DPF based on the regeneration temperature, and may be stored in the controller. The SCR inlet gas target temperature (T _{SCR_in_target} ) can be estimated using an SCR inlet gas target temperature model previously built through experiments and evaluations, and the SCR inlet gas target temperature model is the DPF outlet gas temperature and a map capable of predicting the SCR inlet gas target temperature (T _{SCR_in_target} ) based on the set target temperature range (or the highest temperature value of the set target temperature range) and stored in the controller. In addition, the temperature of the cooling air (T _cool ) can be predicted using a cooling air temperature model previously built through experiments and evaluations, and the cooling air temperature model is based on the outlet temperature of the intercooler 134 and the supercharger ( 120) and the outlet temperature of the LP-EGR cooler 146, it can be configured as a map capable of predicting the temperature Tcool of the cooling air and stored in the controller. At this time, the DPF outlet gas temperature T _{DPF_out} is estimated as a temperature value of the exhaust gas passing through the DPF 140 before supplying cooling air between the DPF 140 and the SCR 142, and the SCR inlet gas temperature The target temperature (T _{SCR_in_target} ) is estimated as a target temperature value of the gas (exhaust gas + cooling air) supplied to the inlet side of the SCR (142) to ensure the optimal purification efficiency of the SCR (142), and the temperature of the cooling air (T _cool ) is estimated as a temperature value of cooling air supplied between the SCR 142 and the DPF 140 in order to reduce the temperature of the inlet gas of the SCR 142 to the target temperature T _{SCR_in_target} .

Next, the controller determines the estimated DPF outlet gas temperature (T _{DPF_out} ), SCR inlet gas target temperature (T _{SCR_in_target} ), cooling air temperature (T _cool ), and DPF passing gas flow rate ( ) Based on the supply flow rate of cooling air supplied between the SCR and DPF ( ) is calculated. Supply flow rate of the cooling air ( ) can be calculated as in Equation 1 below.

Equation 1:

In Equation 1 above, the gas flow rate passing through the DPF ( ) is the exhaust gas flow rate value passing through the DPF per unit time, and is determined as the sum of the intake flow rate of the engine intake line measured by the HFM sensor and the amount of fuel injected into the engine combustion chamber during DPF regeneration (main injection + after injection) do. Supply flow rate of the cooling air ( ), the specific heat of the cooling air supplied between the SCR (142) and the DPF (140) through the LP-EGR flow path (144) and the specific heat of the exhaust gas passing through the DPF (140) and flowing toward the inlet side of the SCR (142) are Assume the same.

As described above, the supply flow rate of cooling air ( After calculating ), the controller determines and controls the boost pressure (P _boost ) of the engine intake line generated by the compressor 114 of the turbocharger (specifically, between the compressor of the turbocharger and the compressor of the supercharger). . The boost pressure (P _boost ) is the intake air flow rate required for engine driving when the DPF 140 is regenerated and the supply flow rate of the cooling air ( ) is determined as a pressure value for generating the total flow rate value in the engine intake line, and the boost pressure (Pboost) can be controlled.

Next, the controller determines the number of revolutions (rotational speed) of the motor of the electric supercharger 120 for controlling the supply pressure (P _cool ) of the cooling air. To determine and control the number of rotations of the motor, the controller first estimates and determines the supply pressure (P _cool ) of the cooling air. The supply pressure of the cooling air (P _cool ) is the supply flow rate of the cooling air ( ) and DPF outlet pressure (P _{DPF_out} ). The DPF outlet pressure P _{DPF_out} is a pressure value of exhaust gas flowing at the outlet side of the DPF 140 and can be estimated using a DPF outlet pressure model previously built through experiments and evaluations. The DPF outlet pressure model is the gas flow rate through the DPF ( ) as an input value, it can be configured as a map for determining the DPF outlet pressure (P _{DPF_out} ) and stored in the controller.

The supply pressure (P _cool ) of the cooling air is determined to be a value greater than a certain value than the DPF outlet pressure (P _{DPF_out} ), and the pressure difference (target pressure difference) causes the cooling air to flow between the DPF 140 and the SCR ( 142) can be supplied between them.

In order to generate the target pressure difference, the controller controls the pressure ratio (γ _eBooster ) is calculated, and the pressure ratio (γ _eBooster ) and the supply flow rate of cooling air ( ), the number of revolutions of the motor of the supercharger 120 is determined and controlled. The pressure ratio (γ _eBooster ) can be calculated as in Equation 2 below.

Equation 2:

It is assumed that P _{intercooler_out} is the outlet pressure of the intercooler 134, P _cool is the supply pressure of cooling air, and the outlet pressure P _{intercooler_out} of the intercooler 134 is equal to the boost pressure P _boost . .

In addition, the motor rotation speed can be estimated using a pre-built motor rotation speed model, and the motor rotation speed model is based on the pressure ratio (γ _eBooster ) and the supply flow rate of cooling air ( ) as an input value, it can be configured as a map for determining the number of revolutions of the motor and stored in the controller.

The supply pressure of the compressed air discharged from the compressor 122 of the supercharger by driving the supercharger motor 124 at the motor rotation speed determined as described above (ie, the supply pressure of cooling air for lowering the gas temperature at the inlet side of the SCR ( P _cool )) can be controlled to a level that can be supplied between the SCR 142 and the DPF 140.

Since the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited to the above-described embodiments, and various modifications and modifications of those skilled in the art using the basic concept of the present invention defined in the following claims Improvements are also included in the scope of the present invention.

100: engine 110: turbocharger
112: turbine for turbocharger 114: compressor for turbocharger
120: electric supercharger 122: compressor for supercharger
124: motor for supercharger 130: air cleaner
132: LP-EGR valve 134: intercooler
136: bypass flow path 138: bypass valve
140: diesel particulate filter (DPF) 142: nitrogen oxide reduction device (SCR)
144: LP-EGR Euro 146: LP-EGR Cooler
148: cooling air flow path 150: flow control valve
152: intake manifold 154: intake manifold inlet flow path
156: throttle valve 158: HP-EGR valve
160: exhaust manifold 162: HP-EGR euro
164: urea injector

Claims (7)

a regeneration determination step of determining whether to regenerate a diesel particulate filter (DPF) installed in an engine exhaust line;
When the DPF is regenerated, a temperature control step of controlling the inlet gas temperature of the nitrogen oxide reduction device (SCR) disposed at the outlet side of the DPF within a target temperature range set to ensure exhaust purification efficiency of the SCR; contains,
In the temperature control step,
The supply flow rate of cooling air supplied between the DPF and the SCR to reduce the temperature of the gas at the inlet of the SCR to within the target temperature range ( ) A first step of calculating;
The calculated supply flow rate between the DPF and the SCR ( ) A second step of controlling the number of revolutions of the motor of the electric supercharger for pressurizing the cooling air;
A control method for securing exhaust purification efficiency of an engine system, comprising:
delete The method of claim 1,
In the first step, the gas flow rate passing through the DPF ( ), the DPF outlet gas temperature (T _{DPF_out} ), the SCR inlet gas target temperature (T _{SCR_in_target} ), and the cooling air supply flow rate (T _cool ) based on ) A control method for securing exhaust purification efficiency of an engine system, characterized in that for calculating
The method of claim 3,
Supply flow rate of the cooling air ( )silver

A control method for securing exhaust purification efficiency of an engine system, characterized in that calculated by
The method of claim 1,
In the second step,
DPF outlet pressure (P _{DPF_out} ) and supply flow rate of cooling air ( Determining a supply pressure (P _cool ) of the cooling air as a pressure value higher than a predetermined value or more than a DPF outlet pressure (P _{DPF_out} ) based on );
The engine intake flow rate and the supply flow rate of the cooling air ( ) determining a boost pressure (P _boost ) of engine intake supplied to the electric supercharger side based on the sum of the flow rates;
Determining a motor rotational speed of the electric supercharger based on a pressure ratio (γ _eBooster ) between the cooling air supply pressure (P _cool ) and the boost pressure (P _boost ) and the cooling air supply pressure (P _cool ) ;
A control method for securing exhaust purification efficiency of an engine system, comprising:
The method of claim 5,
The pressure ratio (γ _eBooster ) is

A control method for securing exhaust purification efficiency of an engine system, characterized in that calculated by
The method of claim 6,
The motor rotation speed of the electric supercharger is determined by a motor rotation speed model configured to determine the motor rotation speed based on the pressure ratio (γ _eBooster ) and the cooling air supply pressure (P _cool ). A control method for securing exhaust purification efficiency of an engine system.

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