Method and device for controlling an engine system

Abstract

A method of controlling an engine system having a continuously variable valve timing (CVVD) device (80) and an exhaust gas recirculation (EGR) device (70), the method comprising: Determining whether an EGR valve (73) of the EGR device (70) is open; Determining an amount of external EGR gas in response to an opening of the EGR valve (73) and an amount of internal EGR gas in response to an actuation of the CVVD device (80) when the EGR valve (73) is open; Comparing a value determined by summing the amount of external EGR gas and the amount of internal EGR gas with an EGR limit value; and Reducing a lift duration of an intake valve (14) when the value determined by summing the amount of external EGR gas and the amount of internal EGR gas is greater than the EGR limit value, wherein the amount of external EGR gas is determined based on a pressure difference between a front end portion and a rear end portion of the EGR valve (73) and an opening amount of the EGR valve (73), and wherein the internal EGR gas is determined based on a difference between an intake pressure and an exhaust pressure and a valve overlap between the intake valve (14) and an exhaust valve (15).

Description

Background of the inventionTechnical field

[0001] The present invention relates to a method and apparatus for controlling an engine system. More specifically, the present invention relates to a method and apparatus for controlling an engine system with a continuously variable valve duration (CVVD) device and exhaust gas recirculation (EGR) that can improve combustion stability and combustion efficiency. Description of related technology

[0002] An internal combustion engine generates power by burning fuel in a combustion chamber in an air medium drawn into the chamber. Intake valves are actuated by a camshaft to take in the air, and the air is drawn into the combustion chamber while the intake valves are open. Exhaust valves are also actuated by the camshaft, and a fuel gas is expelled from the combustion chamber while the exhaust valves are open.

[0003] Optimal operation of the intake and exhaust valves depends on the engine's rotational speed. This means that the optimal lift or optimal opening or closing timing of the valves depends on the engine's rotational speed. To achieve optimal valve actuation depending on the engine's rotational speed, various research projects have been conducted, such as designing multiple cams and continuously variable valve lift (CVVL), which can change the valve lift depending on the engine speed.

[0004] To achieve such optimal valve operation depending on the engine's rotational speed, research has also been conducted on a continuously variable valve timing (CVVT) device that enables different valve timing operations depending on the engine speed. The general CVVT can change valve timing with a fixed valve opening duration.

[0005] However, the general CVVL and CVVT are complicated in their structure and also expensive in terms of manufacturing costs.

[0006] Therefore, research has been conducted on a continuously variable valve duration (CVVD) device that can adjust a lift duration of a valve depending on an operating condition of the engine.

[0007] An exhaust gas recirculation (EGR) device returns a portion of the exhaust gas emitted by the combustion chamber back to the chamber.

[0008] In order to use the CVV device and the EGR device in the engine system, a method is needed to diagnose whether the CVVD device and the EGR device are working normally.

[0009] Examples of previously known configurations can be found, among others, in DE 10 2012 209 911 A1, DE 10 2013 212 988 A1 and US 2015 / 0 192 079 A1.

[0010] The information disclosed in this Background of the Invention section is provided merely to enhance understanding of the general background of the invention and should not be considered as an admission or any form of suggestion that this information constitutes prior art already known to one skilled in the art. Short summary

[0011] Various aspects of the present invention are directed to providing a method and apparatus for controlling an engine system, having the advantages of being suitable for improving combustion stability and combustion efficiency of an engine system having a continuously variable valve timing (CVVD) device and an exhaust gas recirculation (EGR) device.

[0012] This object is achieved by a method having the features of claim 1, a method having the features of claim 7, a device having the features of claim 4, and / or a device having the features of claim 8. Further embodiments emerge from the dependent claims.

[0013] A method for controlling an engine system with a continuously variable valve timing (CVVD) device and an exhaust gas recirculation (EGR) device according to an exemplary embodiment of the present invention includes: determining whether an EGR valve of the EGR device is open; determining an amount of external EGR gas depending on an opening of the EGR valve and an amount of internal EGR gas depending on an actuation of the CVVD device when the EGR valve is open; comparing a value determined by summing the amount of external EGR gas and the amount of internal EGR gas with an EGR threshold; and decreasing the lift duration of an opening valve when the value determined by summing the amount of external EGR gas and the amount of internal EGR gas is greater than the EGR threshold.

[0014] The amount of external EGR gas is determined based on a pressure difference between a front end portion and a rear end portion of the EGR valve, and an opening amount of the EGR valve.

[0015] The internal EGR gas is determined based on a difference between an intake pressure and an exhaust pressure and a valve overlap between the intake valve and an exhaust valve.

[0016] The method may further comprise: comparing the intake valve lift duration to a threshold; and maintaining an operating state of the CVVD device when the intake valve lift duration reaches the threshold.

[0017] The method may further comprise maintaining an operating state of the CVVD device when the value determined by summing the amount of external EGR gas and the amount of internal EGR gas is equal to or less than the EGR threshold.

[0018] An apparatus for controlling an engine system with a continuously variable valve timing (CVVD) device and an exhaust gas recirculation (EGR) device according to an exemplary embodiment of the present invention includes: a pressure difference detector configured to detect a pressure difference between a front end portion and a rear end portion of an EGR valve; an internal pressure detector configured to detect an internal pressure; an external pressure detector configured to detect an external pressure;and a controller for determining whether the EGR valve is open and determining an amount of external EGR gas depending on an opening of the EGR valve and an amount of internal EGR gas depending on an actuation of the CVVD device, wherein the controller is configured to compare a value determined by summing the amount of external EGR gas and the amount of internal EGR gas with an EGR threshold, and to reduce a lift duration of an intake valve if the value determined by summing the amount of external EGR gas and the amount of internal EGR gas is greater than the EGR threshold;

[0019] The controller detects the external EGR gas based on the pressure difference between the front end portion and the rear end portion of the EGR valve and an opening amount of the EGR valve.

[0020] The controller determines the internal EGR gas based on a difference between the intake pressure and the exhaust pressure and a valve overlap between the intake valve and an exhaust valve.

[0021] The controller may compare the intake valve lift duration with a threshold value, and maintain an operating state of the CVVD device when the intake valve lift duration reaches the threshold value.

[0022] The controller may maintain an operating state of the CVVD device when the value obtained by summing the amount of the external EGR gas and the internal EGR gas is equal to or less than the EGR threshold.

[0023] A method for controlling an engine system with a continuously variable valve timing (CVVD) device and an exhaust gas recirculation (EGR) device according to another exemplary embodiment of the present invention may include: determining whether an EGR valve of the EGR device is open; determining an amount of external EGR gas in response to an actuation of the EGR valve and an amount of internal EGR gas in response to an actuation of the CVVD device when the EGR valve is open; comparing a value determined by summing the amount of external EGR gas and the amount of internal EGR gas with an EGR threshold; and decreasing a lift duration of an exhaust valve when the value determined by summing the amount of external EGR gas and the amount of internal EGR gas is greater than the EGR threshold.

[0024] The amount of external EGR gas is determined based on the pressure difference between the front end and rear end of the EGR valve, and the opening amount of the EGR valve. The internal EGR gas is determined based on the difference between the intake pressure and the exhaust pressure, and the valve overlap between the intake valve and the exhaust valve.

[0025] An apparatus for controlling an engine system with a continuously variable valve timing (CVVD) device and an exhaust gas recirculation (EGR) device according to another exemplary embodiment of the present invention includes: a pressure difference detector configured to detect a pressure difference between a front end portion and a rear end portion of an EGR valve; an internal pressure detector configured to detect an internal pressure; an external pressure detector configured to detect an external pressure;and a controller that determines whether the EGR valve is open and determines an amount of EGR gas depending on the EGR valve, and an amount of internal EGR gas depending on an operation of the CVVD device, wherein the controller compares a value determined by summing the amount of external EGR gas and the amount of internal EGR gas with an EGR threshold and decreases a lift duration of an exhaust valve when the value determined by summing the amount of external EGR gas and the amount of internal EGR gas is greater than the EGR threshold;

[0026] The controller determines the external EGR gas based on the pressure difference between the front end and rear end of the EGR valve and the opening amount of the EGR valve. The controller determines the internal EGR gas based on the difference between the intake pressure and the exhaust pressure and the valve overlap between the intake valve and an exhaust valve.

[0027] According to an exemplary embodiment of the present invention, an internal EGR gas is adjusted by operating a continuously variable valve timing (CVVD) device, improving combustion stability and combustion efficiency of an engine.

[0028] The methods and apparatus of the present invention have other features and advantages which will be apparent from or further explained in the accompanying figures provided herein and the following detailed description, which together serve to explain certain principles of the present invention. Short description of the characters Fig. 1 is a schematic figure of an engine system according to an exemplary embodiment of the present invention. Fig. 2 is a block diagram of an apparatus for controlling an engine system according to an exemplary embodiment of the present invention. Fig. 3 is a flowchart illustrating a method for controlling an engine system according to an exemplary embodiment of the present invention.

[0029] It should be understood that the accompanying figures are not necessarily to scale and are a somewhat simplified representation of various features illustrating the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, positioning and orientation, and shapes, will be determined in part by the specific intended application and use environment.

[0030] Reference numerals in the figures refer to the same or equivalent parts of the present invention throughout the various figures of the drawings.

[0031] Reference will now be made in detail to various embodiments of the present invention, examples of which are shown in the accompanying figures and described below. While the invention will be described in connection with exemplary embodiments, it is to be understood that the present description is not intended to limit the invention to these exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents, and other embodiments that may fall within the spirit and scope of the invention as defined by the accompanying claims.

[0032] Hereinafter, exemplary embodiments of the present application will be described in more detail with reference to the accompanying figures, which show exemplary embodiments of the present invention. However, the present invention is not limited to the exemplary embodiments disclosed herein and may be modified in various ways.

[0033] The figures and description are to be considered as illustrative and not restrictive. Corresponding reference numerals designate corresponding elements throughout the description. Configurations shown in the figures are shown randomly for clarity and ease of description, but the present invention is not limited thereto.

[0034] Fig. 1 is a schematic diagram of an engine system according to an exemplary embodiment of the present invention, and Fig. 2 is a block diagram of an apparatus for controlling an engine system according to an exemplary embodiment of the present invention.

[0035] With reference to Fig. 1 and Fig. 2, an engine system according to an exemplary embodiment of the present invention may include an engine 10, a turbocharger 20, an intake conduit 30, a throttle valve 40, a first exhaust conduit 50, a second exhaust conduit 60, an exhaust gas recirculation (EGR) device 70, and a continuously variable valve timing (CVVD) device 80.

[0036] The engine 10 burns fuel and air to convert chemical energy into mechanical energy. The engine 10 has a cylinder 11, a piston 12, a crankshaft 13, an intake valve 14, and an exhaust valve 15.

[0037] The piston 12 and the crankshaft 13 are mounted in the cylinder 11. The piston 12 reciprocates due to the explosive force of the fuel and rotates the crankshaft 13. A combustion chamber 16 is formed between the cylinder 11 and the piston 12.

[0038] The engine 10 is connected to the intake passage 30 for taking in air, and exhaust gas generated in a combustion process is discharged to the outside of the engine 10 through the first exhaust passage 50. The intake passage 30 is opened or closed by the intake valve 14, and the first exhaust passage 50 is opened or closed by the exhaust valve 15. The intake valve 14 can be actuated by an intake cam 81 of the CVVD device 80, and the exhaust valve 15 can be actuated by an exhaust cam 83.

[0039] An injector 17 injects fuel into the combustion chamber 16, and a spark plug 18 ignites a gas mixture in which the fuel and air are mixed.

[0040] A coolant temperature sensor 11a, a knock sensor 11b, and a crankshaft position sensor 11c are mounted on the cylinder 11. The coolant temperature sensor 11a detects a coolant temperature and transmits a signal corresponding thereto to a controller 100. The knock sensor 11b detects vibration and transmits a signal corresponding thereto to the controller 100, and the controller 100 determines whether knocking occurs based on the signal from the knock sensor 11b. The crankshaft position sensor 11c detects a rotation angle of the crankshaft 13 and transmits a signal corresponding thereto to the controller 100, and the controller 100 determines an engine speed based on the signal from the crankshaft position sensor 11c.

[0041] The turbocharger 20 includes a turbine 21 and a compressor 22. The turbine 21 can rotate due to the exhaust gas, and the compressor 22 can rotate due to power generated by rotation of the turbine 21.

[0042] The intake line 30 supplies air to the engine 10. As the compressor 22 rotates, air entering from the outside is compressed to be supplied to the internal combustion engine. Therefore, the compressed air is supplied to boost the power of the engine 10. To cool the air passing through the compressor 22, an intercooler 31 may be attached to the intake line 30.

[0043] The throttle valve 40 is attached to the intake pipe 30, and an air flow supplied from the intake pipe 30 to the engine is controlled depending on an opening degree of the throttle valve 40.

[0044] An intake pressure sensor 94 is mounted on the intake line 30 between the throttle valve 40 and the engine 10 and detects an intake pressure to transmit a signal corresponding thereto to the controller 100.

[0045] The first exhaust pipe 50 discharges the exhaust gas emitted by the engine 10 to the outside of a vehicle. A catalyst 51 may be attached to the first exhaust pipe 50 to reduce harmful components of the exhaust gas.

[0046] The second exhaust line 60 is configured such that a portion of the exhaust gas is combined with the first exhaust line 50 via the turbine 21. The amount of exhaust gas passing through the turbine 21 is controlled depending on the opening amount of a wastegate valve 52 attached to the first exhaust line 50.

[0047] An exhaust pressure sensor 95 is attached to the first exhaust line 50 and detects an exhaust pressure in order to transmit a corresponding signal to the controller 100.

[0048] The EGR device 70 may include an EGR line 71, an EGR cooler 72, and an EGR valve 73.

[0049] The EGR line 71 may provide communication downstream of the catalyst 51 and at the intake line 30. A portion of the exhaust gas emitted by the catalyst 51 may be recirculated to the engine 10 via the EGR line 79.

[0050] The EGR cooler 72 is attached to the EGR line 71 for cooling the exhaust gas supplied to the intake line 30.

[0051] The EGR valve 73 is attached to the EGR passage 71. When the EGR valve 73 is opened, a portion of the exhaust gas discharged from the catalyst 51 can be re-supplied to the engine 10 via the EGR passage 71. When the EGR valve 73 is closed, the exhaust gas discharged from the catalyst 51 is not re-supplied to the engine 10 via the EGR passage 71. An exhaust gas supplied to the intake passage 30 via the EGR passage 71 depending on an opening amount of the EGR valve 73 is referred to as an external EGR gas.

[0052] The CVVD device 80 adjusts a lift period of the intake valve 14. The CVVD device 80 includes the intake cam 81 and the camshaft 82. The CVVD device 80 can change a relative rotation speed of the intake cam 81 with respect to the camshaft 82. In other words, the lift period of the intake valve 14 decreases or increases depending on the operation of the CVVD device 80. Since the CVVD device 80 is described in KR 10 1 655 228 B1, detailed descriptions thereof are omitted. Furthermore, it should be understood that the entire contents contained in KR 10 1 655 228 B1 are incorporated by reference in their entirety into the present specification.The CVVD device 80 described in KR 10 1 655 228 B1 is an example of a continuously variable valve timing (CVVD) device to which the scope of the present invention can be applied, and the scope of the present invention can be applied to various CVVD devices, including the CVVD device 80 described in KR 10 1 655 228 B1.

[0053] Valve overlap, which is a portion where the intake valve 14 and the exhaust valve 15 are opened simultaneously, occurs in response to operation of the CVVD device 80, and therefore, a portion of the exhaust gas discharged from the combustion chamber 16 can be supplied back to the combustion chamber 16. Exhaust gas supplied to the combustion chamber 16 in response to the operation of the CVVD device 80 is referred to as internal EGR gas. A temperature of the combustion chamber 16 can be reduced using the internal EGR gas. In an exemplary embodiment of the present invention, it is shown that the CVVD device 80 adjusts the lift period of the intake valve 14, but the scope of the present invention may be applied to a case where the CVVD device 80 adjusts a lift period of the exhaust valve 15.

[0054] An apparatus for controlling an engine system according to an exemplary embodiment of the present invention may include a data detector 90, a controller 100, the EGR valve 73, and the CVVD device 80.

[0055] The data detector 90 acquires data for controlling the engine system, and the data acquired by the data detector 90 is transmitted to the controller 100. The data detector 90 may include a pressure difference sensor 91, an intake pressure sensor 92, and an exhaust pressure sensor 93. The data detector 90 may further include sensors for controlling the engine system (for example, an accelerator pedal position sensor, a brake pedal position sensor, a vehicle speed sensor, etc.).

[0056] The pressure difference sensor 91 detects a pressure difference between a front end portion and a rear end portion of the EGR valve 73 and transmits a corresponding signal to the controller 100.

[0057] The intake pressure sensor 92 detects an intake pressure of air flowing into the engine 10 and transmits a corresponding signal to the controller 100.

[0058] The exhaust pressure sensor 93 detects an exhaust pressure of exhaust gas emitted from the engine 10 and transmits a signal corresponding thereto to the controller 100.

[0059] The controller 100 may determine an amount of external EGR gas based on the signal from the pressure difference sensor 91 and the opening amount of the EGR valve 73. In addition, the controller 100 may determine an amount of internal EGR gas based on the signal from the intake pressure sensor 92, the signal from the exhaust pressure sensor 93, and the valve overlap depending on the operation of the CVVD device 80. The controller 100 may be implemented with at least one processor executed by a predetermined program, and the predetermined program may include a series of instructions for executing each step included in a method for controlling an engine system according to an exemplary embodiment of the present invention. Further, the controller 100 may control operations of the EGR valve 73 and the CVVD device 80 based on the data acquired by the data detector 90.

[0060] Fig. 3 is a flowchart illustrating a method for controlling an engine system according to an exemplary embodiment of the present invention.

[0061] As in Fig. 3, the controller 100 determines a lift duration of the intake valve 14 depending on an engine speed and an engine load, and actuates the CVVD device 80 to implement the predetermined lift duration of the intake valve 14 at step S100.

[0062] The controller 100 determines whether the EGR valve 73 is open at step S110. The EGR valve 73 may be opened when the engine 10 is operating in a high-load range.

[0063] When the EGR valve 73 is opened at step S110, the controller 100 determines an amount A1 of external EGR gas based on the opening of the EGR valve 73 and an amount A2 of internal EGR gas based on an actuation of the CVVD device 80 at step S120. The controller 100 may determine the amount A1 of external EGR gas based on the pressure difference between the front end portion and the rear end portion of the EGR valve 73 and an opening amount of the EGR valve 73. Furthermore, the controller 100 may determine the amount A2 of internal EGR gas based on a difference between the intake pressure and the exhaust pressure and the valve overlap between the intake valve 14 and the exhaust valve 15.

[0064] The controller 100 compares a value A3, which is determined by summing the amount A1 of external EGR gas and the amount A2 of internal EGR gas, with an EGR threshold value B at step S130. The EGR threshold value B can be determined through experimentation, taking into account combustion efficiency and combustion stability of the engine 10. If exhaust gas of the EGR threshold value or more is supplied to the engine 10, misfire may occur or combustion stability may be deteriorated.

[0065] If the value A3 obtained by summing the amount A1 and the amount A2 is greater than the EGR threshold B at step S130, the controller 100 actuates the CVVD device 80 to decrease the lift duration of the intake valve 14 at step S140. As the lift duration of the intake valve 14 decreases, the valve overlap decreases, and the amount A2 of internal EGR gas is reduced. The amount of reduction in the lift duration of the intake valve 14 can be determined through an experiment taking into account combustion efficiency and combustion stability of the engine 10.

[0066] The controller 100 compares the intake valve lift duration with a threshold value at step S150. For example, the threshold value may be a minimum intake valve lift duration suitable for implementation by actuating the CVVD device 80.

[0067] If the lift duration of the intake valve 14 is greater than the threshold value at step S150, the controller 100 may execute steps S110 and later again. Steps S110 to S140 are performed iteratively, and therefore the lift duration of the intake valve 14 gradually decreases.

[0068] When the lift duration of the intake valve 14 reaches the threshold at step S150, the controller 100 may maintain an operating state of the CVVD device 80 at step S160. In this case, the lift duration of the intake valve 14 may be maintained at the minimum lift duration.

[0069] However, if the value A3 obtained by summing the amount A1 and the amount A2 is equal to or less than the EGR threshold B at step S130, the controller 100 may maintain an operating state of the CVVD device 80 at step S160. In this case, the lift duration of the intake valve 14 may be maintained at a lift duration suitable for maximizing combustion efficiency of the engine 10.

[0070] In an exemplary embodiment of the present invention, it is shown that the CVVD device adjusts the lift duration of the intake valve 14, but also in a case where the CVVD device 80 adjusts a lift duration of the exhaust valve 15, the internal EGR gas can be adjusted with the method for controlling an engine system comprising steps S100 to S160.

[0071] As described above, according to the exemplary embodiment of the present invention, the internal EGR gas can be adjusted by operation of the CVVD device 80, which improves combustion stability and combustion efficiency of the engine 10.

[0072] For ease of description and precise definition in the accompanying claims, the terms "upper", "lower", "inner", "outer", "top", "bottom", "upper", "lower", "upward", "downward", "front", "rear", "back", "inside", "outside", "inward", "outward", "inside", "external", "internal", "outer", "forward" and "backward" are used to describe features of the exemplary embodiments with reference to the positions of such features as shown in the figures.

[0073] The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to restrict or limit the invention to the specifically disclosed forms, and it is evident that numerous modifications and variations are possible in light of the above teachings. The exemplary embodiments have been shown and described in order to explain certain principles of the invention and their practical application in order to enable one skilled in the art to make and use various exemplary embodiments of the present invention, as well as various modifications and alternatives thereto. It is to be understood that the scope of the invention is defined by the appended claims.

Claims

[1] A method of controlling an engine system having a continuously variable valve timing (CVVD) device (80) and an exhaust gas recirculation (EGR) device (70), the method comprising: Determining whether an EGR valve (73) of the EGR device (70) is open; Determining an amount of external EGR gas in response to an opening of the EGR valve (73) and an amount of internal EGR gas in response to an actuation of the CVVD device (80) when the EGR valve (73) is open; Comparing a value determined by summing the amount of external EGR gas and the amount of internal EGR gas with an EGR limit value; and Reducing a lift duration of an intake valve (14) when the value determined by summing the amount of external EGR gas and the amount of internal EGR gas is greater than the EGR limit value, wherein the amount of external EGR gas is determined based on a pressure difference between a front end portion and a rear end portion of the EGR valve (73) and an opening amount of the EGR valve (73), and wherein the internal EGR gas is determined based on a difference between an intake pressure and an exhaust pressure and a valve overlap between the intake valve (14) and an exhaust valve (15). [2] The method of claim 1, further comprising: Comparing the lift time of the intake valve (14) with a threshold value; and Maintaining an operating state of the CVVD device (80) when the lift time of the intake valve (14) reaches the threshold value. [3] A method according to any one of the preceding claims, further comprising: Maintaining an operating state of the CVVD device (80) when the value determined by summing the amount of external EGR gas and the amount of internal EGR gas is equal to or less than the EGR limit value. [4] An apparatus for controlling an engine system having a continuously variable valve timing (CVVD) device (80) and an exhaust gas recirculation (EGR) device (70), the apparatus comprising: a pressure difference detector (91) adapted to detect a pressure difference between a front end portion and a rear end portion of an EGR valve (73); an inlet pressure detector (92) adapted to detect an inlet pressure; an exhaust pressure detector (93) suitable for detecting an exhaust pressure; and a controller (100) adapted to determine whether the EGR valve (73) is open and to determine an amount of external EGR gas in dependence on an opening of the EGR valve (73) and an amount of internal EGR gas in dependence on an operation of the CVVD device (80), wherein the controller (100) is adapted to compare a value determined by summing an amount of external EGR gas and an amount of internal EGR gas with an EGR limit value, and to reduce a lift duration of an intake valve (14) if the value determined by summing the amount of external EGR gas and the amount of internal EGR gas is greater than the EGR limit value, wherein the controller (100) is adapted to determine the external EGR gas based on the pressure difference between the front end portion and the rear end portion of the EGR valve (73) and an opening amount of the EGR valve (73), and wherein the controller (100) is adapted to determine the internal EGR gas based on a difference between the intake pressure and the exhaust pressure and a valve overlap between the intake valve (14) and an exhaust valve (15). [5] The apparatus of claim 4, wherein the controller (100) is adapted to compare the lift duration of the intake valve (14) with a threshold value and is adapted to maintain an operating state of the CVVD device (80) when the lift duration of the intake valve (14) reaches the threshold value. [6] The apparatus according to claim 4 or 5, wherein the controller (100) is adapted to maintain an operating state of the CVVD device (80) when the value obtained by summing the amount of the external EGR gas and the internal EGR gas is equal to or less than the EGR limit value. [7] A method of controlling an engine system having a continuously variable valve timing (CVVD) device (80) and an exhaust gas recirculation (EGR) device (70), the method comprising: Determining whether an EGR valve (73) of the EGR device (70) is open; determining an amount of external EGR gas depending on an opening of the EGR valve (73) and an amount of internal EGR gas depending on an actuation of the CVVD device (80) when the EGR valve (73) is open; Comparing a value determined by summing the amount of external EGR gas and the amount of internal EGR gas with an EGR limit value; and Reducing a lift duration of an exhaust valve (15) when the value determined by summing the amount of external EGR gas and the amount of internal EGR gas is greater than the EGR limit value, wherein the amount of external EGR gas is determined based on a pressure difference between a front end portion and a rear end portion of the EGR valve (73) and an opening amount of the EGR valve (73), and wherein the internal EGR gas is determined based on a difference between an intake pressure and an exhaust pressure and a valve overlap between the intake valve (14) and an exhaust valve (15). [8] An apparatus for controlling an engine system having a continuously variable valve timing (CVVD) device (80) and an exhaust gas recirculation (EGR) device (70), the apparatus comprising: a pressure difference detector (91) adapted to detect a pressure difference between a front end portion and a rear end portion of an EGR valve (73); an inlet pressure detector (92) adapted to detect an inlet pressure; an exhaust pressure detector (93) suitable for detecting an exhaust pressure; and a controller (100) adapted to determine whether the EGR valve (73) is open and to determine an amount of external EGR gas in dependence on an opening of the EGR valve (73) and an amount of internal EGR gas in dependence on an operation of the CVVD device (80), wherein the controller (100) is adapted to compare a value determined by summing an amount of external EGR gas and an amount of internal EGR gas with an EGR limit value, and to reduce a lift duration of an exhaust valve (15) if the value determined by summing the amount of external EGR gas and the amount of internal EGR gas is greater than the EGR limit value, wherein the controller (100) is adapted to determine the external EGR gas based on the pressure difference between the front end portion and the rear end portion of the EGR valve (73) and an opening amount of the EGR valve (73), and wherein the controller (100) is adapted to determine the internal EGR gas based on a difference between the intake pressure and the exhaust pressure and a valve overlap between the intake valve (14) and an exhaust valve (15).

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