Apparatus and method of controlling engine system

A control apparatus of an engine system, the engine system including an engine, a VGT configured to control a boost pressure applied to the engine by adjust an angle of a vane provided in a turbine, and an EGR valve configured to control an amount of a recirculated exhaust gas, includes a target value determiner determining a target boost pressure and a target intake air amount based on an engine speed and a fuel injection amount, an EGR valve controller calculating a target EGR mass flow rate based on the target boost pressure and the target intake air amount and determining an EGR valve opening rate, and a turbocharger controller performing a sliding mode control using the calculated target EGR mass flow rate as a parameter to calculate a target compressor power and a target turbocharger mass flow rate and determining a turbine vane opening rate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC §119 to Korean Patent Application No. 10-2014-0051696, filed on Apr. 29, 2014 in the Korean Intellectual Property Office (KIPO), the contents of which are herein incorporated by reference in their entirety.

BACKGROUND

Example embodiments relate to an apparatus for controlling an engine system and a method of controlling the same. More particularly, example embodiments relate to an apparatus and method of controlling a boost pressure and an intake air amount in a diesel engine.

2. Description of the Related Art

Currently, diesel engines may be equipped with a variable geometry turbocharger in which a turbine is rotated by an exhaust gas flowing in an exhaust pipe and a compressor connected to the turbine via a shaft is rotated to compress an intake air, thereby perform supercharging. Also, the diesel engines may be equipped with an exhaust gas recirculation (EGR) system which recirculates a portion of the exhaust gas to a combustion chamber to efficiently reduce NOx.

In a conventional engine management system, PID (proportional integral derivative) controller dedicated to VGT (variable geometry turbocharger) and PID controller dedicated to EGR may be used independently to each other.

A conventional PID controller may have lookup tables for P, I, D gain and use optimal P, I, D gain adapted for a working situation. However, a huge number of tests may be required to obtain the optimal lookup table, to thereby increasing development periods and costs.

Further, since the variable geometry turbocharger (VGT) and the EGR system may be physically coupled to each other, a coupling effect of VGT and EGR may need to be considered together. However, a conventional controller in the diesel engine system may ignore the coupling effect and control the VGT and EGR independently, so that it may be difficult to perform a precise and accurate control, especially in a transient operation.

SUMMARY

Example embodiments provide a control apparatus of an engine system capable of reducing a controller tuning time and improving a control performance.

Example embodiments provide a method of controlling an engine system using the above control apparatus.

According to example embodiments, a control apparatus of an engine system, the engine system including an engine, a variable geometry turbocharger having a turbine and a compressor and configured to control a boost pressure applied to the engine by adjust an angle of a vane provided in the turbine, and an exhaust gas recirculation (EGR) valve configured to control an amount of an exhaust gas recirculated to the engine, includes a target value determiner determining a target boost pressure and a target intake air amount based on an engine speed and a fuel injection amount, an EGR valve controller calculating a target EGR mass flow rate based on the target boost pressure and the target intake air amount and determining an EGR valve opening rate according to the calculated target EGR mass flow rate, and a turbocharger controller performing a sliding mode control using the target EGR mass flow rate calculated based on the target boost pressure as a parameter to calculate a target compressor power and a target turbocharger mass flow rate and determining a turbine vane opening rate according to the calculated turbocharger mass flow rate.

In example embodiments, the EGR valve controller may include a target EGR flow rate calculator calculating the target EGR flow rate using an intake manifold model on the basis of the target boost pressure and the target intake air amount and an EGR valve lift calculator calculating the EGR valve opening rate according to the calculated target EGR mass flow rate.

In example embodiments, the EGR valve controller may further include an EGR flow rate corrector which corrects the calculated target EGR flow rate in consideration of environmental conditions.

In example embodiments, the turbocharger controller may include a target compressor power calculator performing a sliding mode control using a difference between the target boost pressure and a current boost pressure as a sliding control error to calculate the target compressor power, a target turbocharger flow rate calculator performing a sliding mode control using a difference between the target compressor power and a current compressor power as a sliding control error to calculate the target turbocharger mass flow rate, and a turbocharger vane position calculator calculating the turbine vane opening rate according to the target turbocharger mass flow rate.

According to example embodiments, in a method of controlling an engine system, a target boost pressure and a target intake air amount are determined based on an engine speed and a fuel injection amount. A target EGR mass flow rate is calculated based on the target boost pressure and the target intake air amount. An EGR valve opening rate is calculated according to the target EGR mass flow rate. A sliding mode control is performed using the target EGR mass flow rate calculated based on the target boost pressure as a parameter to calculate a target compressor power and a target turbocharger mass flow rate. A turbine vane opening rate is calculated according to the target turbocharger mass flow rate.

In example embodiments, the method may further include correcting the target EGR mass flow rate in consideration of environmental conditions.

In example embodiments, calculating the target compressor power and the target turbocharger mass flow rate may include performing a sliding mode control using a difference between the target boost pressure and a current boost pressure as a sliding control error to calculate the target compressor power, and performing a sliding mode control using a difference between the target compressor power and a current compressor power as a sliding control error to calculate the target turbocharger mass flow rate.

According to example embodiments, a control apparatus of an engine system may control a boost pressure and an intake air amount in a diesel engine using model based control. In an engine system including a turbocharger and an EGR system physically coupled with each other, the control apparatus may control a vane opening rate of the turbocharger in consideration of a target EGR mass flow rate. Thus, the control apparatus may reduce a controller tuning time and improve a control performance.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a block diagram illustrating a control apparatus of an engine system in accordance with example embodiments.FIG. 2is a block diagram illustrating a controller inFIG. 1.

Referring toFIGS. 1 and 2, an engine system may include an internal combustion engine10, a variable geometry turbocharger (VGT)30disposed between an intake pipe20and an exhaust pipe22and supercharging intake air by exhaust power, an exhaust gas recirculation system40configured to recirculate a part of an exhaust gas from an exhaust manifold16to the engine10, and a controller50executing various controls of the engine system.

In example embodiments, the engine10may include a diesel engine as a driving source for a construction machine, for example, excavator. The engine10may include a plurality of cylinders12respectively having a combustion chamber, into which a fuel is injected by a fuel injection device (not illustrated). The intake air may be distributed to the cylinders12through an intake manifold14, and the exhaust gas exhausted from the cylinders12may flow into the exhaust pipe22through the exhaust manifold16.

The variable geometry turbocharger30may be connected to the exhaust manifold16through the exhaust pipe22and connected to the intake manifold14through the intake pipe20. The variable geometry turbocharger30may supply the turbocharged intake air to the intake manifold14and exhaust the exhaust gas from the exhaust manifold16to the outside.

In particular, the variable geometry turbocharger30may include a turbine32arranged in the exhaust pipe22and rotated by the exhaust gas flowing in the exhaust pipe22and a compressor34operated by the rotational energy of the turbine32. The turbine32may be driven by a pressure of the inflowing exhaust gas, and the rotational force of the turbine32may be transmitted to the compressor34such that the compressor34may compress and deliver the intake air flowing in the intake pipe20to the intake manifold14.

A fresh intake air may be compressed by the compressor34and flow into the intake manifold14of the engine10through an intake air supply pipe24. An intercooler26may be installed in the intake air supply pipe24such that the intake air may be cooled and supplied to the intake manifold14.

The turbine32of the variable geometry turbocharger30may include a vane. An angle of the vane (opening rate of the turbine) may be adjusted by a control signal outputted by the controller50to change a flow rate of the exhaust gas, thereby controlling a boost pressure applied to the engine10.

The EGR system40may include an EGR line42, an EGR valve44and an EGR cooler46. A part of the exhaust gas from the exhaust manifold16of the engine10may be recirculated to the intake manifold14of the engine10through the EGR line42. The EGR valve44may be installed in the EGR line42to control a flow rate of the recirculated exhaust gas. The EGR cooler46may be installed in the EGR line42to cool the recirculated exhaust gas.

An opening rate of the EGR valve44may be adjusted by a control signal outputted by the controller50to change a flow rate of the exhausted gas recirculated to the engine10.

In order to properly adjust the vane opening rate of the VGT turbine32and the opening rate of the EGR valve44, various detection devices and sensors may be provided in the engine system. The controller50may receive various measurements about operating conditions of the engine from the detection devices and sensors. For example, the controller50may receive output signals such as an engine speed (rpm) of the engine10from an engine speed sensor, an fuel injection amount from the fuel injection device, a boost pressure from an intake manifold pressure sensor, an intake manifold temperature from an intake manifold temperature sensor, an exhaust manifold pressure from an exhaust manifold pressure sensor, an exhaust manifold temperature from an exhaust manifold temperature sensor, etc.

The controller50may control the vane of the VGT turbine32and the EGR valve44on the basis of the output signals. As illustrated inFIG. 2, the controller50may include target value determiner51, a measurement/model storage portion52, an EGR valve controller54and a turbocharger controller56.

The target value determiner51may determine a target boost pressure and a target intake air amount based on the engine speed and the fuel injection amount. The target value determiner51may calculate the target boost pressure and the target intake air amount on the basis of a lookup table using the engine speed and the fuel injection amount as input values.

The measurement/model storage portion52may receive and store the measurements about driving conditions of the engine from the detection devices and sensors. The measurements may be inputted to the EGR valve controller54and the turbocharger controller56and used to calculate desired target values. The measurement/model storage portion52may construct and store a system model such as an intake manifold model, an exhaust manifold model of the engine10, etc. The system model may be constructed on the basis of intake and exhaust dynamics of an actual engine, and the constructed system model may be used to calculate desired target values in the EGR valve controller54and the turbocharger controller56.

The EGR valve controller54may calculate a target EGR mass flow rate based on the target boost pressure and the target intake air amount and determine an EGR valve opening rate according to the calculated target EGR mass flow rate. In particular, the EGR valve controller54may include a target EGR flow rate calculator54a, a target EGR flow rate corrector54band an EGR valve lift calculator54c.

The target EGR flow rate calculator54amay calculate the target EGR mass flow rate using the intake manifold model on the basis of the target boost pressure and the target intake air amount.

In the intake manifold model, the sum of a mass of an air flowing into the intake manifold14and a mass of an air exiting from the intake manifold14is zero in a steady state operating condition of a steady state. The law of conservation of mass in the intake manifold14may be expressed by following Equation (1).
ΣW=Wied−Wcid−WEGRd=0  Equation (1)

Here, Wiedis target cylinder intake mass flow rate, Wcidis target compressor mass flow rate, and WEGRdis target EGR mass flow rate.

Accordingly, the target EGR mass flow rate may be calculated using a difference of the cylinder intake mass flow rate and the target intake air amount (compressor mass flow rate) by following Equation (2).
WEGRd=Wied−WcidEquation (2)

The target cylinder intake mass flow rate may be calculated by using speed-density method as known in the art. That is, the target cylinder intake mass flow rate may be calculated using intake manifold temperature/pressure and the engine speed by following Equation (3).

Here, Pidis target boost pressure, N is engine speed, ηvis volumetric efficiency, R is ideal gas constant, and Tiis intake manifold temperature.

In an operating condition, when the target intake air amount (fresh air) is increased abruptly, the target EGR mass flow rate may be reduced in order to supply a desired amount of a fresh air. In an operating condition, when the target boost pressure is increased abruptly, the target cylinder intake air amount may be increased according to the boost pressure increase, and consequently the target EGR mass flow rate may be increased in order to satisfy the target cylinder intake air amount.

The EGR flow rate corrector54bmay correct the calculated target EGR mass flow rate in consideration of environmental conditions. The target EGR mass flow rate may be corrected by flowing Equation (4) in order to reduce an error between the target EGR flow rate and the current EGR flow rate.
WEGR_corrd=(WEGRd−WEGR)·P_gain+∫[(WEGRd−WEGR)·I_gain]dtEquation (4)

Here, WEGR_corrdis corrected target EGR mass flow rate, WEGRis current EGR mass flow rate, P_gain is P gain value for target EGR mass flow rate correction, and I_gain is I gain value for target EGR mass flow rate correction.

As engine characteristics varies according to changes of environment conditions such as ambient temperature, ambient pressure and the like or deterioration of the engine, the error between the target EGR mass flow rate calculated by the EGR flow rate calculator54aand the current EGR mass flow rate may be increased significantly. In this case, in order to harmonize the calculated target EGR mass flow rate with the current EGR mass flow rate, the target EGR mass flow rate may be corrected by using PI control as expressed by Equation (4). The PI control may be performed such that the corrected target EGR mass flow rate may be decreased gradually. The correction of the target EGR mass flow rate may be omitted for simplicity in consideration of the ambient conditions.

The EGR valve lift calculator54cmay calculate the EGR valve opening rate according to the calculated or corrected target EGR mass flow rate.

The EGR valve opening rate (EGR valve lift) may be one of the final output signals of the controller50. Effective flow area (EFA) of the EGR valve44may be calculated using an orifice equation by following Equation (5) and the opening rate of the EGR valve may be determined from EFA on the basis of a lookup table.

As the EGR mass flow rate and EFA are proportional to each other, as expressed in Equation (5), in an operating condition, when the target EGR mass flow rate is increased, EFA may be increased and the EGR valve lift may be increased (opened) accordingly, and when the target EGR mass flow rate is decreased, EFA may be decreased and the EGR valve lift may be decreased (closed) accordingly.

Accordingly, the EGR valve controller54may calculate the opening rate of the EGR valve44on the basis of the target boost pressure and the target intake air amount and output a control signal to the EGR valve44. Thus, the opening rate of the EGR valve44may be adjusted by the control signal to control an amount of the exhaust gas recirculated to the engine10.

The turbocharger controller56may perform a sliding mode control using the target EGR mass flow rate calculated based on the target boost pressure as a parameter to calculate a target compressor power and a target turbocharger mass flow rate and determine a turbine vane opening rate according to the calculated turbocharger mass flow rate. In particular, the turbocharger controller56may include a target compressor power calculator56a, a target turbocharger flow rate calculator56band a turbocharger vane position calculator56c.

The target compressor power calculator56amay perform a sliding mode control using a difference between the target boost pressure and a current boost pressure as a sliding control error to calculate the target compressor power.

The difference between the current boost pressure and the target boost pressure may be defined as a sliding control error (sliding surface) S1as expressed by following Equation (6) and, a sliding mode control (SMC) algorism may be performed such that S1converges to zero.
S1=pi−pidEquation (6)

The SMC algorism may be expressed by following Equation (6-1)

Here, η0and Φ0are a controller gain and a constant.

An SMC controller may control such that the control error S1, that is, the boost pressure control error, may stay near zero.

Equation (6) may be substituted to Equation (6-1) to obtain following Equation (7), and then, following Equation (8) as dynamics equation for intake manifold pressure may be substituted to the left-hand side of Equation (7) to obtain following Equation (9).

The compressor mass flow rate and the cylinder intake mass flow rate in the left-hand side of Equation (9) may be expressed by following Equation (10) and following Equation (11) respectively, Equation (10) and Equation (11) may be substituted to Equation (9) to obtain following Equation (12), and consequently, the target compressor power may be expressed by following Equation (13).

As expressed in Equation (13), in case that the sliding control error S1is a positive number, the current boost pressure may be greater than the target boost pressure. The greater is S1(the greater is the difference between the current boost pressure and the target boost pressure), the less is the target compressor power. The target compressor power may be controlled to be decreased to reduce the supercharged amount and to reach the target boost pressure.

The target turbocharger flow rate calculator56bmay perform a sliding mode control using a difference between the target compressor power and a current compressor power as a sliding control error to calculate the target turbocharger mass flow rate.

The difference between the current compressor power and the target compressor power may be defined as a sliding control error (sliding surface) S2as expressed by following Equation (14) and, a sliding mode control (SMC) algorism may be performed such that S2 converges to zero.
S2=Pc−PcdEquation (14)

The SMC algorism may be expressed by following Equation (15)

Here, η1and Φ1are a controller gain and a constant.

An SMC controller may control such that the control error S2, that is, the compressor power control error, may stay near zero.

Equation (14) may be substituted to Equation (15) to obtain following Equation (16), and then, following Equation (17) as dynamics equation for compressor power may be substituted to the left-hand side of Equation (16) to obtain following Equation (18).

The turbine power in the left-hand side of Equation (18) may be expressed by following Equation (19), and following Equation (20) representing turbine power characteristics may be substituted to the left-hand side of Equation (19) to obtain following Equation (21) which represents a turbocharger (VGT) mass flow rate required to reach the target value of the compressor power.

As expressed in Equation (21), in case that the current compressor power is greater than the target compressor power, that is, the sliding control error S2is a positive number, the greater is the absolute value of S2, the less is the target VGT mass flow rate. When an occasion to reduce a compressor power arises, an SMC controller may control to make S2converges to zero such that the target VGT mass flow rate may be decreased to thereby reduce the compressor power.

The turbocharger vane position calculator56cmay calculate the turbine vane opening rate according to the target turbocharger mass flow rate.

The VGT vane opening rate may be one of the final output signals of the controller50. Effective flow area (EFA) of the vane provided in the turbine32of the turbocharger30may be calculated using an orifice equation by following Equation (22) and the opening rate of the VGT vane may be determined from EFA on the basis of a lookup table.

As the VGT mass flow rate and EFA are proportional to each other, as expressed in Equation (22), in an operating condition, when the target VGT mass flow rate is increased, EFA may be increased and the opening rate of the VGT vane may be increased (opened) accordingly, and when the target VGT mass flow rate is decreased, EFA may be decreased and the opening rate of the VGT vane may be decreased (closed) accordingly.

Accordingly, the turbocharger controller56may calculate the opening rate of the VGT vane on the basis of the target boost pressure and output a control signal to the VGT vane. Thus, the opening rate of the vane disposed in the VGT turbine32may be adjusted by the control signal to control a boost pressure applied to the engine10.

As mentioned above, a control apparatus of an engine system may control a boost pressure and an intake air amount in a diesel engine using model based control. In an engine system including a turbocharger and an EGR system physically coupled with each other, the control apparatus may control a vane opening rate of the turbocharger in consideration of a target EGR mass flow rate. Thus, the control apparatus may reduce a controller tuning time and improve a control performance.

Hereinafter, a method of controlling an engine system using the control apparatus of an engine system inFIG. 1will be explained.

FIG. 3is a flow chart illustrating a method of controlling the engine system inFIG. 1.

Referring toFIGS. 1 to 3, first, an engine speed and an amount of a fuel injected by a fuel injection device may be detected (S100), and then, a target boost pressure and a target intake air amount may be determined (S102).

The controller50may receive various measurements about operating conditions of the engine from various detection devices and sensors. For example, the controller50may receive output signals such as an engine speed (rpm) of the engine10from an engine speed sensor, a fuel injection amount from the fuel injection device, etc.

The target value determiner51may determine the target boost pressure and the target intake air amount based on the engine speed and the fuel injection amount. The target value determiner51may calculate the target boost pressure and the target intake air amount on the basis of a lookup table using the engine speed and the fuel injection amount as input values.

Then, a target EGR mass flow rate may be calculated based on the target boost pressure and the target intake air amount (S104).

The target EGR flow rate calculator54amay calculate the target EGR mass flow rate using an intake manifold model on the basis of the target boost pressure and the target intake air amount. The intake manifold model may be constructed on the basis of intake dynamics of an actual engine and the like. The target EGR mass flow rate may be calculated using a difference of the cylinder intake mass flow rate and the target intake air amount (compressor mass flow rate).

In example embodiments, the target EGR mass flow rate may be corrected in consideration of environmental conditions (S106).

As engine characteristics varies according to changes of environmental conditions such as ambient temperature, ambient pressure and the like or deterioration of the engine, the error between the target EGR mass flow rate calculated by the EGR flow rate calculator Ma and the current EGR mass flow rate may be increased significantly. In this case, in order to harmonize the calculated target EGR mass flow rate with the current EGR flow rate, the target EGR mass flow rate may be corrected by a feedback control.

Then, an EGR valve opening rate may be calculated according to the calculated or corrected target EGR mass flow rate (S108), and then, an opening rate of an EGR valve may be adjusted (5110).

The EGR valve lift calculator54cmay calculate the EGR valve opening rate according to the calculated or corrected target EGR mass flow rate. The EGR valve opening rate (EGR valve lift) such as one of the final output signals may be calculated by calculating effective flow area (EFA) of the EGR valve44using an orifice equation and by determining the opening rate of the EGR valve from EFA on the basis of a lookup table.

The EGR valve controller54may calculate the opening rate of the EGR valve44on the basis of the target boost pressure and the target intake air amount and output a control signal to the EGR valve44. Thus, the opening rate of the EGR valve44may be adjusted by the control signal to control an amount of the exhaust gas recirculated to the engine10.

On the other hand, a sliding mode control may be performed using the target EGR mass flow rate calculated based on the target boost pressure as a parameter to calculate a target compressor power (S112), and then, a target turbocharger mass flow rate may be calculated (S114).

The target compressor power calculator56amay perform a sliding mode control using a difference between the target boost pressure and a current boost pressure as a sliding control error to calculate the target compressor power.

The target turbocharger flow rate calculator56bmay perform a sliding mode control using a difference between the target compressor power and a current compressor power as a sliding control error to calculate the target turbocharger mass flow rate.

Then, a turbine vane opening rate may be determined according to the target turbocharger mass flow rate (S116), and then, a vane angle of the turbine may be adjusted (S118).

The turbocharger vane position calculator56cmay calculate the turbine vane opening rate according to the target turbocharger mass flow rate. The VGT vane opening rate such as one of the final output signals may be calculated by calculating effective flow area (EFA) of the vane provided in the turbine32of the turbocharger30using an orifice equation and determining the opening rate of the VGT vane from EFA on the basis of a lookup table.

The turbocharger controller56may calculate the opening rate of the VGT vane on the basis of the target boost pressure and output a control signal to the VGT vane. Thus, the opening rate of the vane disposed in the VGT turbine32may be adjusted by the control signal to control a boost pressure applied to the engine10.