Methods and systems for controlling exhaust gas recirculation in engine systems

Abstract

Method for an engine (2), comprising An adjustment of valve control immediately after activation of the external EGR in order to modify the internal EGR in such a way as to compensate for a deviation of the external EGR from a target, characterized by the fact that The valve control is adjusted in time and duration by freely controlling the excitation of an electromagnet in an intake-side adjustable valve actuator (15) for an intake valve (14) and / or an electromagnet in an exhaust-side adjustable valve actuator (35) for an exhaust valve (34), and the current valve timing (VVT) is gradually changed to the target value with an increased input (VVT(i)), which changes stepwise according to the coefficient (k1) which has a time constant (τ1) as a variable, where the time constant (τ1) specifies a period from the moment immediately after the introduction of the entire current mixture inside the intake manifold (17) into the combustion chambers (27) until the moment immediately after the introduction of new external EGR gas up to the predetermined quantity into the intake manifold (17).

Description

TECHNICAL AREA

[0001] The present invention relates to methods and systems for controlling exhaust gas recirculation in an engine system. GENERAL STATE OF THE ART

[0002] To improve fuel economy, engine systems can be equipped with exhaust gas recirculation (EGR) systems, through which at least a portion of the exhaust gas is recirculated to the engine intake manifold. External EGR and a combined internal / external EGR system were used. With external EGR, the amount of EGR gas admitted to the engine intake manifold via an external EGR passage can be varied using an EGR valve. With internal EGR, the amount of residual gas retained in the engine cylinder can be adjusted via negative valve overlap.

[0003] From JP 4 598 289 B2, an engine control system is known in which the valve control is adjusted to increase the internal EGR so that a lack of external EGR is compensated for when the engine demands more than the capacity of the external EGR.

[0004] In an engine system capable of operating with combined internal and external EGR, the negative valve overlap is less significant for operation with external EGR activated than for operation with external EGR deactivated, in order to reduce the amount of internal EGR gas. This strategy is used to maintain combustion stability by preventing the amount of exhaust gas in a combustion chamber from exceeding the level required during operation with external EGR activated.

[0005] A change in the amount of internal EGR gas in a combustion chamber in response to a change in negative valve overlap caused by adjusting the valve timing occurs more rapidly than a change in the amount of external EGR gas in the combustion chamber in response to a change in the EGR valve lift.

[0006] Therefore, the total amount of internal and external EGR gas inside the combustion chamber can be lower than required if the valve timing is set to reduce internal EGR immediately after external EGR is activated. This deficiency in the total amount of internal and external EGR is compensated for by an additional supply of fresh air. This additional fresh air supply causes an increase in the amount of fuel injected, which is controlled by the intake air mass, thus reducing fuel economy.

[0007] DE 10 2007 003 855 A1 discloses a method for controlling exhaust gas recirculation in an internal combustion engine, in which the adjustment of the internally recirculated exhaust gas quantity is carried out by controlling the cam phases depending on engine load and engine speed.

[0008] From JP 2011 - 122 544 A, an internal combustion engine is known which can delay the ignition timing to avoid knocking during combustion without worsening the thermal efficiency of the internal combustion engine by first attempting to suppress knocking via an EGR control or a fuel supply control before ignition timing control is carried out.

[0009] From US patent 2009 / 0312936A1, an engine control system is known which is able to reduce torque fluctuations and the like when switching between a gasoline engine and a compression-ignition engine by reducing the lift and valve opening duration of an intake valve to a value less than a value specified for the compression-ignition combustion mode. BRIEF SUMMARY OF THE INVENTION

[0010] Therefore, it is an object of the present invention to provide a method and a system for an engine wherein the amount of EGR gas inside a combustion chamber is brought into conformity with a target level required by the engine in order to improve fuel economy.

[0011] According to one aspect of the present invention, a method for an engine comprises adjusting a valve control immediately after the activation of the external EGR in order to modify the internal EGR in such a way as to compensate for a deviation of the external EGR from a target, wherein the valve control is adjusted in time and duration by freely controlling the excitation of an electromagnet in an intake-side adjustable valve actuator for an intake valve and / or an electromagnet in an exhaust-side adjustable valve actuator for an exhaust valve.Furthermore, the current valve timing is gradually changed to the target value with an increased input, which changes stepwise according to the coefficient that has a time constant as a variable, where the time constant specifies a period from the moment immediately after the entire current mixture inside the intake manifold is admitted into the combustion chambers until the moment immediately after the introduction of new external EGR gas up to the predetermined quantity into the intake manifold.

[0012] Therefore, one aspect of the present invention can improve the fuel economy of the engine. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation of an exemplary engine system. Fig. Figure 2 is a flowchart for setting a valve control to change the internal EGR immediately after activating the external EGR, according to a first embodiment of the present invention. Fig. 3(a) is an ignition timing adjustment diagram showing the adjustment of the valve control immediately after activation of the external EGR according to the state of the art. Fig. 3(b) is an ignition timing adjustment diagram showing the adjustment of the valve control immediately after activation of the external EGR according to the first embodiment of the present invention. Fig. Figure 4 is a flowchart for setting a valve control to change the internal EGR immediately after activating the external EGR, according to a second embodiment of the present invention. DESCRIPTION OF EXECUTION FORMS

[0013] With reference to the accompanying drawings, the following describe methods and systems for adjusting valve timing immediately after activating or deactivating external EGR in an engine system. Fig. 1 provided. (First embodiment)

[0014] As in Fig. As shown in Figure 1, an engine system 1 comprises an internal combustion engine 2 and an electronic control unit (ECU) 3.

[0015] Engine 2 is a four-cylinder in-line gasoline engine. It should be noted that the number of cylinders in Engine 2 is not limited to four. Furthermore, Engine 2 is not limited to such a four-cylinder in-line engine; it can also take the form of a V-engine.

[0016] This engine 2 comprises a cylinder block 22, a cylinder head 23 attached to an upper part of the cylinder block 22, and an oil pan 24 attached to a lower part of the cylinder block 22. The oil pan 24 stores the engine lubricant.

[0017] The cylinder block 22 is configured with cylinders 25. A piston 26 is housed in each cylinder 25 in such a way that it can move vertically back and forth. Furthermore, a combustion chamber 27 is provided in an upper section of the cylinder 25. The combustion chamber 27 is defined within the cylinder 25 between a head surface of the piston 26 and a lower surface of the cylinder head 23.

[0018] Engine 2 is designed as a so-called four-stroke gasoline engine, which performs four separate strokes that include intake, compression, work and exhaust.

[0019] The pistons 26 are connected to a crankshaft 29 via their connecting rods 28. The connecting rods 28 convert the reciprocating motion of the pistons 26 into a rotary motion of the crankshaft 29. The crankshaft 29 is held rotatably by the cylinder block 22 via crankpins (not shown).

[0020] The cylinder head 23 is equipped with a spark plug 10, an intake port 11, and an exhaust port 12. The spark plug 10 is positioned on the cylinder head 23 such that its electrode protrudes into the combustion chamber 27 to generate a spark with a suitable ignition timing adjustment set by the ECU 3 in response to the engine operating condition of the engine 2. The intake port 11 connects the combustion chamber 27 to an intake passage 16a, which will be described later. Furthermore, an injector 13 and an intake valve 14 are provided with respect to the intake port 11.

[0021] The injector 13 is a so-called port fuel injector, designed to inject fuel, supplied by a fuel pump from a fuel tank (not shown), into the intake port 11. The injector 13 can also be configured as a so-called cylinder injector, designed to inject fuel directly into the combustion chamber 27. The fuel injected into the intake port 11, after mixing with the intake air to form a mixture, is admitted to the combustion chamber 27. The mixture admitted to the combustion chamber 27 is ignited by a spark generated by the spark plug 10. The combustion of this mixture causes a piston 26 to move back and forth in the cylinder 25, thereby rotating a crankshaft 29.

[0022] The intake valve 14 is designed to be opened or closed to provide or block a connection between the intake passage 16a and the combustion chamber 27. The opening and closing of the intake valve 14 can be performed by an adjustable valve actuator 15 on the intake side.

[0023] For the intake-side adjustable valve actuator 15, an electromagnetic adjustable valve actuator can be used, which is capable of opening / closing the intake valve 14 by means of an electromagnetic actuator consisting, for example, of an electromagnet, a spring, and other components. More precisely, the intake-side adjustable valve actuator 15 is designed such that the excitation of the electromagnet attracts a movable part that is fixed to the intake valve 14, which is normally biased in a valve closing direction by a spring.

[0024] Furthermore, the intake-side adjustable valve actuator 15 is electrically connected to the ECU 3 described later in such a way that the excitation and de-excitation of the electromagnet can be controlled by the ECU 3. Therefore, the ECU 3 can modify the valve control of the intake valve 14 as desired in order to easily adjust the valve opening period of the intake valve 14.

[0025] Furthermore, a hydraulically type adjustable valve actuator can be used for the intake-side adjustable valve actuator 15, which uses a hydraulic actuator instead of an electromagnetic actuator. A mechanically type adjustable valve actuator capable of shifting the valve control of the intake valve 14 using cam elements such as a main cam and an auxiliary cam can also be used for the intake-side adjustable valve actuator 15.

[0026] Additionally, this intake-side adjustable valve actuator 15 can be designed in such a way that it continuously changes the valve lift of the intake valve 14 together with the valve control of the intake valve 14 by, for example, adjusting an excitation current to the electromagnet by the ECU 3.

[0027] An intake manifold 17 is provided on the intake port side of the cylinder head 23. An intake pipe 16 is coupled to the intake manifold 17. This intake pipe 16 defines an intake passage 16a, which is connected to the intake port 11 via the intake manifold 17. A manifold pressure sensor 19, an electronically controlled throttle valve 18, and an intake air volume sensor 20 are provided along the intake passage 16a in that order, from the downstream side to the upstream side with respect to the intake direction, i.e., the direction in which fresh air is admitted. The throttle valve 18 is electrically connected to the ECU 3.

[0028] The throttle valve 18, whose throttle position is regulated by the ECU 3 in response to a command signal, is designed to adjust the amount of intake air supplied to the engine 2. The manifold pressure sensor 19 is positioned to detect the intake air pressure. The intake air volume sensor 20 is positioned to detect the airflow of the fresh intake air.

[0029] On the other hand, an exhaust valve 34 is provided in the exhaust port 12. The exhaust valve 34 is designed to be opened or closed in order to provide a connection between an exhaust passage 36a, described later, and the combustion chamber 27, or to block the connection. The opening and closing of the exhaust valve 34 can be carried out by an adjustable valve actuator 35 on the exhaust side.

[0030] The exhaust-side adjustable valve actuator 35, which has the same design as the previously described intake-side adjustable valve actuator (therefore a detailed description is omitted), can arbitrarily modify the valve control of the exhaust valve 34, since the excitation and de-excitation of an electromagnet can be controlled by the ECU 3. Therefore, the ECU 3 can easily adjust the valve opening period of the exhaust valve 34.

[0031] An exhaust manifold 37 is provided on the exhaust port side of the cylinder head 23. An exhaust pipe 36 is connected to the exhaust manifold 37. This exhaust pipe 36 defines an exhaust passage 36a, which is connected to the exhaust port 12 via the exhaust manifold 37.

[0032] This engine 2 has an exhaust gas recirculation (EGR) passage 41, which provides a connection between the intake manifold 17 and the exhaust manifold 37. The EGR passage 41 is arranged to recirculate a portion of the exhaust gas back to the intake side. The EGR passage 41 is equipped with an EGR valve 42. The EGR valve 42 is electrically connected to the ECU 3. The EGR valve 42 is designed to adjust the amount of exhaust gas to be recirculated back to the intake side by regulating its valve lift (i.e., the degree of valve opening) in response to a command signal from the ECU 3. EGR operation using the EGR passage 41 is referred to as "external EGR". Furthermore, exhaust gas recirculated back to the intake side through the EGR passage 41 is referred to as "external EGR gas".

[0033] The operating state of engine 2 is controlled by the ECU 3. The ECU 3 comprises a microcomputer that includes, for example, a central processing unit (CPU), random access memory (RAM), read-only memory (ROM), an input / output interface (I / O), and other components. The CPU is designed to use a temporary storage function of the RAM and to perform signal processing according to programs that have been pre-stored in the ROM. The ROM pre-stores data such as various control parameters and various planning data or characteristic maps.

[0034] Various sensors, such as the manifold pressure sensor 19, the intake air volume sensor 20 (described previously), and a crankshaft angle sensor 36, are connected to the input port of the ECU 3. It should be noted that the crankshaft angle sensor 38 detects the rotation angle of the crankshaft 29. Based on the measured value supplied by the crankshaft angle sensor 38, the ECU 3 calculates the engine speed. Furthermore, based on the signal from the intake air volume sensor 20, the ECU 3 calculates the amount of intake air per unit of time (intake air volume) and determines the load on the engine 2 from this intake air volume.

[0035] On the other hand, the spark plug 10, the injector 13, the throttle valve 18, the intake-side adjustable valve actuator 15, the exhaust-side adjustable valve actuator 35 and the EGR valve 42, which were described above, are coupled to the output port side of the ECU 3.

[0036] Furthermore, the ECU 3 includes a valve control unit 31. The valve control unit 31 sets the valve opening periods of the intake valve 14 and the exhaust valve 34 by controlling the intake valve 14 and exhaust valve 34 valve control unit by controlling the intake-side adjustable valve actuator 15 and the exhaust-side adjustable valve actuator 35 described above, which means, for example, that it advances or delays the valve closing time of the intake valve 14 and the exhaust valve 34.

[0037] Furthermore, the valve control unit 31 sets an overlap period, which specifies an overlap between the valve opening period of the intake valve 14 and the valve opening period of the exhaust valve 34, in response to the engine speed and engine load. The valve control unit 31 is configured to perform internal EGR by controlling the valve timing of the intake valve 14 and the exhaust valve 34, whereby a portion of the exhaust gas discharged from the exhaust port 12 is introduced as internal EGR gas into the combustion chamber 27, the intake port 11, and the intake manifold 17.

[0038] A target quantity of the total EGR gas quantity of the external EGR gas and the internal EGR gas is experimentally determined in response to the operating state of engine 2, and the quantity of the external EGR gas and the quantity of the internal EGR gas are controlled on the basis of this determined target quantity.

[0039] The ECU 3 is designed to determine whether the external EGR is activated or deactivated in response to the operating state of the engine 2. For example, the ECU 3 uses an external EGR map, which provides a setting based on engine speed and load, to determine whether the external EGR should be activated or deactivated. This map is divided into an activation range, where the external EGR is enabled, and a deactivation range, where the external EGR is disabled. The map can be consulted based on engine speed and load to determine which of these ranges corresponds to the current operating state. This external EGR map was experimentally determined in advance and is stored in the ROM of the ECU 3.

[0040] The valve control unit 31 of the ECU 3 is configured to regulate the amount of internal EGR in response to the operating state of the engine 2. For example, the valve control unit 31 regulates the amount of internal EGR by controlling the valve timing of the intake valve 14 and the exhaust valve 34 using a valve timing map that provides valve timing determined according to engine speed and engine load. The ROM of the ECU 3 stores one experimentally determined valve timing map for the range of external EGR deactivation and another experimentally determined valve timing map for the range of external EGR activation.

[0041] The valve control map for the external EGR deactivation range is a map used when no external EGR gas is admitted. This valve control map for the external EGR deactivation range is set such that the amount of internal EGR gas is increased by lengthening the overlap period.

[0042] The valve timing map for the external EGR activation range is a map used when external EGR gas is introduced. This valve timing map is set to reduce the amount of internal EGR gas by shortening the overlap period when external EGR gas is to be introduced, since the total amount of EGR gas from the external and internal EGR gases determines the combustion limit of the fuel.

[0043] The ECU 3 activates the external EGR by opening the EGR valve 42 when, after consulting the external EGR map based on a value of the engine speed and that of the engine load, it determines that the current operating condition falls within the range for external EGR activation. This causes external EGR gas to be recirculated through the EGR passage 41 into the intake manifold 17.

[0044] The ECU 3 then determines a valve lift or valve position for the EGR valve 42, for example, by consulting an EGR valve position map. This map specifies the valve lift or position required for an optimal amount of EGR gas, depending on the operating conditions determined by engine speed and load. The ECU 3 regulates the valve lift of the EGR valve 42 to achieve the specified EGR valve lift or valve position. This EGR valve position map is experimentally determined in advance and stored in the ROM of the ECU 3.

[0045] Simultaneously, the ECU 3 retrieves the valve control map for the external EGR activation range and regulates the valve control of the intake valve 14 and the exhaust valve 34. The EGR gas quantity through the external EGR and the EGR gas quantity through the internal EGR are regulated in such a way that the total EGR gas quantity reaches the target quantity suitable for the operating state of engine 2 when the external EGR is activated in this manner.

[0046] On the other hand, the ECU 3 deactivates the external EGR by completely closing the EGR valve 42 when, after looking up the external EGR map according to a value of the engine speed and that of the engine load, it determines that the current operating condition falls within the range of deactivation of the external EGR.

[0047] Simultaneously, the ECU retrieves the valve control map for the external EGR deactivation range and regulates the valve control of intake valve 14 and exhaust valve 34. The internal EGR is regulated in such a way that the EGR gas quantity reaches the target quantity suitable for the operating state of engine 2 when the external EGR is deactivated in this manner.

[0048] The ECU 3 adjusts the valve timing, known as variable valve timing (VVT), of the intake valve 14 and the exhaust valve 34 to a predetermined extent over a period from the moment immediately after external EGR activation until the moment immediately after external EGR gas is introduced into the intake manifold 17. This adjustment gradually alters (reduces) the internal EGR in such a way as to compensate for any deviation of the external EGR from a target, i.e., a target quantity of EGR gas. This allows the total amount of external and internal EGR gas in the combustion chamber 27 to be maintained at the target EGR gas quantity. This VVT adjustment process is repeated at predefined sampling intervals.Calculated data, such as the VVT, is stored during the execution of the processing that modifies the VVT ​​for use in the next execution of the processing that modifies the VVT.

[0049] The ECU 3 calculates a time constant τ1, which is expressed by equation (1). The time constant τ1 specifies the period from the moment immediately after the entire current mixture inside the intake manifold 17 is admitted into the combustion chamber 27 until the moment immediately after new external EGR gas is admitted up to the predetermined quantity into the intake manifold 17. τ1[s]=Intake manifold volume[L]÷(fresh intake air volume[L / s]+EGR flow rate[L / s])

[0050] In the equation above, the intake manifold volume is uniquely determined by design values ​​for engine 2. The fresh intake air volume is the volume of fresh air admitted to the intake manifold 17 per second and is calculated based on the signal from the intake air volume sensor 20.

[0051] If the EGR gas flow is expressed as a one-dimensional flow of a compressible fluid (i.e., a flow expressed by a formula that only considers a change in the direction of the flow), the EGR flow is expressed by equation (2). EGR flow rate[L / s]=C×EGR maximum flow rate[L / s]

[0052] In the equation above, C, which represents the characteristic curve of the converging nozzle of the EGR valve 42, is determined by a map that provides retrievable values ​​which change with different values ​​of a pressure ratio of (pressure on the downstream side of the EGR valve [kPa]) ÷ (pressure on the upstream side of the EGR valve [kPa]). This map was determined experimentally in advance and stored in the ROM of the ECU 3.

[0053] The pressure on the downstream side of the EGR valve is calculated using equation (3). Pressure on the downstream side of the EGR valve [kPa] = manifold pressure [kPa] + pressure loss due to friction in the EGR passage [kPa]

[0054] In the equation above, the pressure loss resulting from EGR friction is a value determined by a map that provides retrievable values ​​which change with different values ​​of the EGR gas flow rate through the EGR passage 41. This map was experimentally determined in advance and stored in the ROM of ECU 3. The manifold pressure is determined based on a value measured by the manifold pressure sensor 19. The pressure at the upstream side of the EGR valve is determined by a map that provides retrievable values ​​which change with different combinations of engine speed and engine load. This map was experimentally determined in advance and stored in the ROM of ECU 3.

[0055] The maximum EGR flow rate is defined as the maximum flow rate [L / s] passing through the EGR valve 42 with respect to a given value of the opening cross-sectional area ratio (ratio of the opening cross-sectional area to the cross-sectional area of ​​the EGR valve 42) and is determined by a characteristic map that provides retrievable values ​​which change with different values ​​of the opening cross-sectional area ratio. This characteristic map is experimentally determined in advance and stored in the ROM of the ECU 3.

[0056] The valve control unit 31 determines a coefficient k1 from the time constant τ1 using the following equation (4), which represents the rate of change of time during VVT. Coefficient k1 = Sampling period [s] ÷ Time constant [τ1] × Coefficient k2

[0057] The coefficient k2 is determined by a map that provides retrievable values ​​which change with different combinations of engine speed and engine load. This map is experimentally determined in advance and stored in the ROM of ECU 3. The values ​​of the coefficient k2 are set such that the higher either the engine speed or the load, or both, the greater the coefficient k2. The sampling period is a time interval at which the processing for changing the VVT ​​is repeated.

[0058] Using this coefficient k1, the valve control unit 31 calculates the required VVT, i.e., the VVT ​​after processing for change, using the following equation (5). Required VVT(i) = required VVT(i−l) + coefficient k1 × (target−VVT−required VVT(i−l))

[0059] The required VVT(i-1) is the required VVT calculated during the previous execution of the processing for changing the VVT. It should be noted that immediately after external EGR is activated, no required VVT is stored from the previous execution. Therefore, the required VVT for the external EGR deactivation range, determined by looking up the valve timing map for the external EGR deactivation range according to engine speed and engine load, is used as the required VVT from the previous execution.

[0060] The target VVT is determined by the valve control map for the range of external EGR activation and therefore specifies the corresponding VVT according to the engine speed and engine load.

[0061] The ECU 3 regulates the valve control of the intake valve 14 and the exhaust valve 34 in such a way that the calculated required VVT(i) is achieved.

[0062] This causes the required VVT to gradually approach the target VVT over time. The larger the coefficient k1, the faster the required VVT approaches the target VVT.

[0063] Since the valve timing of the intake valve 14 and the exhaust valve 34 is set or adjusted in this way in response to a change in the amount of external EGR immediately after the external EGR is activated, a lack of external EGR or a deviation from a target amount of EGR gas is compensated for by the internal EGR. This can prevent a shortage of EGR gas, thereby limiting an increase in the fuel injection quantity to improve the fuel economy of engine 2.

[0064] With reference to Fig. Section 2 describes a flowchart for adjusting the valve timing immediately after activating the external EGR. The program starts when ECU 3 is activated and repeats with a predetermined sampling period.

[0065] First, after confirming the external EGR deactivation range by looking up the external EGR map according to engine speed and load, the program determines whether the external EGR deactivation range has been replaced by the external EGR activation range (steps S11 and S12). It should be noted that if the external EGR deactivation range is not confirmed in step S11, the program repeats the same process until confirmation is received. Furthermore, if step S12 does not determine that the external EGR deactivation range has been replaced by the external EGR activation range, the program repeats the same process until confirmation is received.

[0066] If, in steps S11 and S12, it is confirmed that the external EGR deactivation range has been replaced by the external EGR activation range, the time constant τ1 is determined in step S13 using equation (1).

[0067] Next, in step S14, the coefficient k1 is determined from the time constant τ1 using equation (4), and the required VVT is determined using this coefficient k1 and equation (5). It should be noted that the determined required VVT is stored in the RAM of ECU 3 so that it can be referenced during processing in the next period. In step S15, the valve timing of intake valve 14 and exhaust valve 34 is adjusted to achieve the determined required VVT(i). Adjusting the valve timing in step S15 involves setting one or more of the intake valve timing, exhaust valve timing, and the degree of valve overlap. For example, the adjustment might involve retarding the intake valve opening time and / or advancing the exhaust valve closing time to reduce valve overlap.

[0068] Next, it is determined whether the required VVT has become equal to a target VVT (step S16). If it is not determined that the required VVT is equal to the target VVT, the program returns to step S14 and repeats the processing.

[0069] If, on the other hand, it is determined that the required VVT is equal to the target VVT, the stored value resulting from the processing is initialized (step S17), and the program returns to step S11 and repeats the processing.

[0070] With reference to Fig. Section 3 describes how the embodiment described above works. Fig. 3(a) is a timing diagram showing the valve control setting immediately after activation of external EGR according to the state of the art. Fig. 3(b) is a timing diagram showing the valve control setting immediately after activation of external EGR according to the present embodiment. For each Fig. 3(a) and Fig. Figure 3(b) shows the top diagram as the EGR rate caused by external EGR inside the intake manifold 17. The middle diagram shows a change in VVT. The bottom diagram shows a change in the combined EGR rate of external and internal EGR inside the combustion chamber 27. It is noted that the EGR rate indicates the proportion of EGR gas in the mixture inside the intake manifold 17 or the combustion chamber 27.

[0071] As shown in the top diagram of Fig. As shown in Figure 3(a), the EGR rate caused by the external EGR inside the intake manifold 17 gradually approaches the EGR rate for the external EGR activation range immediately after the external EGR is activated at time T1, and reaches the EGR rate for the external EGR activation range at time T2. The conventional control approach to this situation, as shown in the middle diagram, proposes an immediate change in VVT to a VVT value for the external EGR activation range. As shown in the bottom diagram, this causes the overall EGR rate to remain lower than the target EGR rate from immediately after the external EGR activation until the external EGR gas supply stabilizes.In this case, the lack of EGR gas in relation to the target EGR rate is compensated for by an additional supply of fresh air charge, which causes an increase in the amount of fuel injection controlled by the intake air mass, allows the introduction of more fresh air than required, and thereby worsens the fuel economy of engine 2.

[0072] Since in the present embodiment, as shown in the mean time setting diagram of Fig. As shown in Figure 3(b), the VVT ​​is modified according to changes in the EGR rate inside the intake manifold 17, making it possible to maintain the overall EGR rate at the target EGR rate immediately after activation of the external EGR as shown in the bottom timing setting diagram, which prevents the introduction of more fresh air than required and thereby improves the fuel economy of the engine 2.

[0073] In this way, according to the present embodiment, the valve control of the intake valve and the exhaust valve 34 is adjusted in such a way that the total amount of the external EGR gas and that of the internal EGR gas is kept at the target amount immediately after activation of the external EGR.

[0074] This causes the amount of internal EGR gas to be adjusted so that the total amount of external EGR gas and the amount of internal EGR gas are maintained at the target quantity. This allows the target quantity of EGR gas to be admitted to engine 2, thus preventing the introduction of more fresh air than necessary and thereby improving the fuel economy of engine 2.

[0075] Although in the present embodiment the VVT ​​is adjusted by changing the valve control of the intake valve 14 and the exhaust valve 34, the VVT ​​can be adjusted by changing only the valve control of one of the valves while leaving the valve control of the other valve unchanged. (Second embodiment)

[0076] Next, with reference to Fig. 4 A second embodiment is described. Since the present embodiment is similar to the embodiment described above, the drawings are used to describe only the characterizing part, using the same reference numerals to denote identical parts.

[0077] In an engine system of Fig. 1. The ECU 3 adjusts the variable valve timing (VVT) of an intake valve 14 and an exhaust valve 34 for a period from immediately after the external EGR is deactivated until all the external EGR gas remaining inside an intake manifold 17 and an EGR passage 41 has disappeared, in such a way that the internal EGR is gradually modified (increased) to compensate for the deviation of the external EGR from its target quantity. This maintains the quantity of EGR gas in the combustion chamber 27, resulting from the addition of external EGR gas to the internal EGR gas, at a target quantity by gradually modifying the VVT ​​so that the quantity of EGR gas in the combustion chamber 27, resulting from the addition of external EGR gas to the internal EGR gas, equals the target quantity.

[0078] It should be noted here that the time constant τ1 expressed by equation (1) can be expressed by the following equation (1)', since the external EGR is deactivated and the EGR flow rate is zero. τ1[s] = Intake manifold volume [L] ÷ Fresh intake air volume [L / s]

[0079] The ECU then determines the required VVT using equations (4) and (5) in the same way as in the first embodiment.

[0080] With reference to Fig. Section 4 describes a flowchart for adjusting the valve timing immediately after deactivating the external EGR. The program starts with the activation of ECU 3 and is repeated with a predetermined sampling period.

[0081] First, after confirming the external EGR activation range by consulting the external EGR map based on engine speed and load, the program determines whether the external EGR activation range has been replaced by the external EGR deactivation range (steps S21 and S22). It should be noted that if the external EGR activation range is not confirmed in step S21, the program repeats the same process until confirmation is received. Furthermore, if step S22 does not determine that the external EGR activation range has been replaced by the external EGR deactivation range, the program repeats the same process until confirmation is received.

[0082] If, in steps S21 and S22, it is confirmed that the external EGR activation range has been replaced by the external EGR deactivation range, the time constant τ1 is determined in step S23 using equation (1)'.

[0083] As in the first embodiment, in step S14 the coefficient k1 is determined from the time constant τ1 using equation (4), and the required VVT is determined using this coefficient k1 and equation (5). In step S15, the valve timing of the intake valve 14 and the exhaust valve 34 is adjusted to achieve the determined required VVT(i). Adjusting the valve timing in step S15 involves adjusting one or more of the intake valve timing, the exhaust valve timing, and the degree of valve overlap. For example, the adjustment may involve retarding the intake valve opening time and / or advancing the exhaust valve closing time to reduce valve overlap.

[0084] Next, it is determined whether the specified required VVT has become equal to a target VVT (step S16). If it is not determined that the required VVT is equal to the target VVT, the program returns to step S14 and repeats the processing.

[0085] If, on the other hand, it is determined that the required VVT is equal to the target VVT, the stored value resulting from the processing is initialized (step S17), and the program returns to step S11 and repeats the processing.

[0086] In this way, according to the present embodiment, the valve control of the intake valve and the exhaust valve 34 is adjusted in such a way that the total amount of the external EGR gas and that of the internal EGR gas is maintained at the target amount immediately after deactivation of the external EGR by completely closing the EGR valve 42.

[0087] This causes the amount of internal EGR gas to be adjusted so that the total amount of external EGR gas and the amount of internal EGR gas are kept at the target level. This suppresses the introduction of an excessive amount of internal EGR gas while external EGR gas remains, thus preventing misfires resulting from combustion instability.

[0088] Although one embodiment of the present invention has been described, it will be obvious to a person skilled in the art that modifications can be made without departing from the scope of the present invention. All such modifications and their equivalents are to be covered by the following claims, which are described within the scope of the claims. EXPLANATION OF REFERENCE SYMBOLS 1 vehicle 2 Engine 11 Intake opening 12 Outlet opening 14 Intake valve 15 Intake-side adjustable valve actuator 19 Manifold pressure sensor 20 Intake air volume sensor 27 Combustion chamber 31 Valve control unit 34 Exhaust valve 35 exhaust-side adjustable valve actuator 38 Crank angle sensor 41 Exhaust gas recirculation (EGR) passage 42 EGR valve

Claims

[1] Method for an engine (2) comprising An adjustment of valve control immediately after activation of the external EGR in order to modify the internal EGR in such a way as to compensate for a deviation of the external EGR from a target, characterized by , that The valve control is adjusted in time and duration by freely controlling the excitation of an electromagnet in an intake-side adjustable valve actuator (15) for an intake valve (14) and / or an electromagnet in an exhaust-side adjustable valve actuator (35) for an exhaust valve (34), and the current valve timing (VVT) is gradually changed to the target value with an increased input (VVT(i)), which changes stepwise according to the coefficient (k1) which has a time constant (τ1) as a variable, where the time constant (τ1) specifies a period from the moment immediately after the introduction of the entire current mixture inside the intake manifold (17) into the combustion chambers (27) until the moment immediately after the introduction of new external EGR gas up to the predetermined quantity into the intake manifold (17). [2] Method according to claim 1, wherein disabling the external EGR comprises closing an EGR valve (42) with respect to its seat. [3] Method according to claim 1, wherein activating the external EGR comprises opening an EGR valve (42) with respect to its seat. [4] Method according to claim 1, wherein adjusting the valve control comprises delaying the time of opening the intake valve (14) and / or advancing the time of closing the exhaust valve (34) in order to reduce the valve overlap. [5] Method according to claim 1, wherein adjusting the valve control comprises advancing the time of opening the intake valve (14) and / or delaying the time of closing the exhaust valve (34) in order to increase the valve overlap. [6] Engine system, comprising an engine (2) with an intake manifold and an exhaust manifold; an EGR system comprising an EGR passage (41) for recirculating a portion of the exhaust gas from the exhaust tract to the intake tract via an EGR valve (42); a control unit (3) which is designed to Immediately after activating the external EGR, adjust the valve control so that the internal EGR is modified in such a way as to compensate for any deviation of the external EGR from a target. characterized by , that the control unit (3) is further configured to adjust the valve control in time and duration by freely controlling the excitation of an electromagnet in an intake-side adjustable valve actuator (15) for an intake valve (14) and / or an electromagnet in an exhaust-side adjustable valve actuator (35) for an exhaust valve (34), and to gradually change the current valve timing (VVT) to the target value with an increased input (VVT(i)), which changes stepwise according to the coefficient (k1) which has a time constant (t1) as a variable, where the time constant (τ1) specifies a period from the moment immediately after the introduction of the entire current mixture inside the intake manifold (17) into the combustion chambers (27) until the moment immediately after the introduction of new external EGR gas up to the predetermined quantity into the intake manifold (17).

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