JP2010065592A - Engine system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an engine system for smoothly changing various states by switching of an EGR system. <P>SOLUTION: This engine system has a high pressure EGR means, a low pressure EGR means, and a computer 27. The computer 27 defines an LPEGR area for allowing operation only for the low pressure EGR means, an HPEGR area for allowing operation only for the high pressure EGR means, and a transition area where either or both operations of the low pressure EGR means and the high pressure EGR means, on an engine state plane with an engine speed and a fuel quantity as the orthogonal two axes. The computer 27 determines an operating EGR means by referring to the engine state plane by a present engine speed and a fuel quantity. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an engine system that facilitates changes in various states due to switching of an EGR system.

  Compared to the HPGR (High Pressure EGR) system that recirculates EGR gas from the exhaust manifold (high pressure section) to the intake manifold (high pressure section), a system that performs a larger amount of EGR, the outlet of the turbocharger turbine attached to the exhaust manifold ( An LPEGR (Low Pressure EGR) system that recirculates EGR gas from the low pressure part) to the compressor inlet (low pressure part) of the turbocharger is attracting attention.

  FIG. 15 shows an engine system that performs the conventional LPEGR method. The engine system 151 includes a high-pressure turbocharger 5 in which exhaust gas extracted from an exhaust manifold 3 of the engine 2 is supplied to a turbine 4, and a high-pressure exhaust gas adjustment valve 6 that adjusts exhaust gas that exits from the turbine 4 of the high-pressure turbocharger 5. The exhaust gas switching valve 9 for switching the exhaust gas from the turbine 4 of the high-pressure stage turbocharger 5 and the exhaust gas branched from the exhaust manifold 3 to be supplied to the turbine 8 of the low-pressure stage turbocharger 7, and the exhaust gas switching valve 9 The low-pressure stage turbocharger 7 in which the turbine 8 is driven by exhaust gas, the exhaust gas discharge pipe 10 connecting the outlet of the turbine 8 of the low-pressure stage turbocharger 7 to the atmosphere, and the exhaust gas exhaust pipe 10 inserted into the particulate form from the exhaust gas DPF (Diesel Paticulate Filter) 11 for removing substances and exhaust gas exhaust pipe 10 for exhaust A NOx catalytic nitrogen oxide removing device 12 for removing nitrogen oxides from the gas, a low pressure EGR pipe 17 branched from the exhaust gas discharge pipe 10 using the exhaust gas after passing through the DPF 11 as an EGR gas, and the low pressure EGR pipe 17 The low pressure EGR cooler 18 inserted in the low pressure EGR pipe 17, the low pressure EGR valve 19 for adjusting the amount of EGR gas in the low pressure EGR pipe 17, and the compressor 20 of the low pressure stage turbocharger 7 are connected to the low pressure EGR pipe 17. The intake pipe 21, the intake throttle (throttle valve) 22 inserted to the atmosphere side from the junction of the low pressure EGR pipe of the intake pipe 21, and the output of the compressor 20 of the low pressure stage turbocharger 7 are connected to the high pressure stage turbocharger 5. Low pressure turbo output gas piping 24 connected to the input of the compressor 23 and high pressure turbo charge An intake switching valve 25 that switches between the output of the compressor 5 of the compressor 5 and the output of the compressor 20 of the low-pressure stage turbocharger 7, and a high-pressure gas pipe 26 that supplies the gas selected by the intake switching valve 25 to the intake manifold 13 of the engine 2. Is provided.

  The engine system 151 employs a two-stage turbo system in which the turbocharger is provided in two stages, but the outline of the LPEGR is the same even in a single turbo system with only one stage of the turbocharger.

  The engine system 151 is controlled by the computer 27. The computer 27 inputs sensor signals necessary for EGR control, such as engine speed, engine air amount (also referred to as intake air amount), and engine fuel amount (also referred to as fuel input amount; hereinafter referred to as fuel amount). Yes. The computer 27 can output a drive signal to an actuator necessary for EGR control, such as an actuator of the exhaust gas switching valve 9, an actuator of the low pressure EGR valve 19, an actuator of the intake air switching valve 25, and an actuator of the high pressure exhaust gas adjustment valve 6.

  In this engine system 151, the exhaust gas that has exited from the turbine 8 of the low-pressure stage turbocharger 7 and passed through the DPF 11 is branched as an EGR gas from the exhaust gas discharge pipe 10, and is returned to the compressor 20 of the low-pressure stage turbocharger 7. The low-pressure EGR pipe 17 has a low-pressure EGR valve 19 upstream from a location where EGR gas merges with fresh air (taken outside air) in the intake pipe 21, and adjusts the opening area of the low-pressure EGR valve 19 (opening adjustment). Thus, the amount of EGR gas to be merged with fresh air is adjusted.

  The opening degree of the low pressure EGR valve 19 is adjusted by sensing the engine speed, the fuel amount, and the intake air amount with a sensor so that the air amount after the EGR gas is loaded on the engine 2 in the computer 27 becomes an appropriate air amount. Is calculated by calculating the opening degree and outputting a drive signal to the actuator of the low pressure EGR valve 19.

  The computer 27 is formed with a map for assigning the intake air amount using the engine speed and the fuel amount as parameters. When the EGR control is not performed, the intake air amount at each engine rotation speed and each fuel amount is M0, and the intake air amount stored in the reference destination by each engine rotation speed and each fuel amount on the map is M (N, Q ), The EGR amount is M (N, Q) −M0. In other words, a value obtained by adding the EGR amount to the intake air amount M0 when the EGR control is not performed is mapped. If the intake air amount M (N, Q) is given for each engine speed and fuel amount, the EGR amount for the engine state is uniquely determined. This is called an intake air amount control method (hereinafter referred to as MAF control method).

  When the load on the engine is low and the pressure difference between the EGR path outlet and the EGR path inlet is minimal, the EGR gas is reduced by narrowing the intake throttle 22 provided upstream from the location where the EGR gas in the intake pipe 21 merges. Reduce the fresh air flowing into the place where. As a result, the pressure at the outlet of the EGR path is lowered, the pressure difference is increased, and the EGR gas is easily introduced into the intake pipe 21.

When the load on the engine increases, the pressure difference between the EGR path outlet and the EGR path inlet increases, so the intake throttle 22 is fully opened. The computer 27 uses the engine speed and the fuel amount as parameters to set the intake throttle 22 An air amount map for assigning the opening is formed. Therefore, when the engine speed and the fuel amount are input, the opening degree of the intake throttle 22 is controlled to the opening degree specified in the air amount map. Under such intake throttle control, the EGR amount (or EGR rate) by the intake air amount control method is adjusted.

  Next, FIG. 16 shows an engine system 161 that performs the conventional HPEGR system. The engine system 161 includes a high-pressure stage turbocharger 5 in which exhaust gas extracted from the exhaust manifold 3 of the engine 2 is supplied to the turbine 4, and a high-pressure exhaust gas adjustment valve 6 that adjusts exhaust gas that exits from the turbine 4 of the high-pressure stage turbocharger 5. The exhaust gas switching valve 9 for switching the exhaust gas from the turbine 4 of the high-pressure stage turbocharger 5 and the exhaust gas branched from the exhaust manifold 3 to be supplied to the turbine 8 of the low-pressure stage turbocharger 7, and the exhaust gas switching valve 9 The low-pressure stage turbocharger 7 in which the turbine 8 is driven by exhaust gas, the exhaust gas discharge pipe 10 connecting the outlet of the turbine 8 of the low-pressure stage turbocharger 7 to the atmosphere, and the exhaust gas exhaust pipe 10 inserted into the particulate form from the exhaust gas DPF 11 for removing substances and nitrogen oxides inserted into exhaust gas exhaust pipe 10 from exhaust gas The NOx catalytic nitrogen oxide removing device 12 to be removed, the high pressure EGR pipe 14 that takes the exhaust gas as EGR gas from the exhaust manifold 3 of the engine 2 and sends it to the intake manifold 13 of the engine 2, and the high pressure EGR pipe 14 are inserted. The high-pressure EGR cooler 15, the high-pressure EGR valve 16 that adjusts the amount of EGR gas in the high-pressure EGR pipe 14, the intake pipe 21 that connects the atmosphere to the compressor 20 of the low-pressure turbocharger 7, and the intake pipe 21 The intake throttle 22, the low pressure turbo output gas pipe 24 connecting the output of the compressor 20 of the low pressure stage turbocharger 7 to the input of the compressor 23 of the high pressure stage turbocharger 5, and the output and low pressure stage of the compressor 23 of the high pressure stage turbocharger 5. The output of the compressor 20 of the turbocharger 7 Ri replaced includes an intake switching valve 25, and a high-pressure gas pipe 26 to provide a selected gas in the intake switching valve 25 to the intake manifold 13 of the engine 2.

  In the engine system 161 in FIG. 16 as well, as in the engine system 151 in FIG. 15, the computer 27 inputs sensor signals necessary for EGR control such as the engine rotation speed, the engine air amount, and the engine fuel amount (fuel amount). A drive signal can be output to an actuator necessary for EGR control, such as an actuator of the exhaust gas switching valve 9, an actuator of the high pressure EGR valve 16, an actuator of the intake air switching valve 25, an actuator of the high pressure exhaust gas adjustment valve 6.

  In recent years, as a combustion method for simultaneously reducing nitrogen oxides (NOx) and soot in exhaust gas, a combustion method (referred to as a PCI combustion method) in which fuel is injected at an early stage and premixed combustion is mainly used. Have been bathed. In the PCI combustion method, a large amount of EGR is generally performed as a means for preventing premature ignition and knocking. The EGR rate is 50 to 80%.

  The problem of the EGR method, the problem of the combustion method, and the problem when these are combined are described below. In addition, the combustion method mainly consisting of diffusion combustion other than the PCI combustion method is referred to as a conventional combustion method.

  In the HPEGR system, EGR gas is extracted from an exhaust manifold upstream of the turbine of the turbocharger, and the EGR gas is put into the intake manifold. This reduces the amount of gas that passes through the turbine of the turbocharger. When compared with the same engine load, the more the EGR is performed, the more the turbo does not work, and the amount of fresh air supercharged by the turbocharger compressor decreases. As a result, light load region (refers to the region represented by the engine speed and fuel amount where the engine is relatively light load; the region where the engine is relatively high load is called the high load region, In the medium load region), the excess air ratio λ cannot be increased greatly even though a relatively large amount of EGR is required to comply with exhaust gas regulations.

  In the LPEGR system, EGR gas is extracted from an exhaust gas discharge pipe downstream of the turbine of the turbocharger, and the EGR gas is put into an intake pipe upstream of the compressor of the turbocharger. For this reason, the entire amount of exhaust gas passes through the turbine of the turbocharger. Therefore, the excess air ratio λ can be increased even with the same EGR amount as compared with the HPEGR system. With the same excess air ratio λ, the EGR rate can be increased. However, on the other hand, soot generated by the combustion by the conventional combustion system passes through the compressor of the turbocharger along with the EGR gas and passes through the intercooler (not shown). For this reason, the compressor blades and the gas passages of the intercooler are contaminated, and the efficiency of the compressor and the cooling capacity of the intercooler are deteriorated over time.

  In the PCI combustion method, NOx and soot are greatly reduced as compared with the conventional combustion method. However, since the PCI combustion method injects fuel at an early stage, it tends to cause excessively early ignition and knocking and can be used only in a light load region. In order to suppress excessive pre-ignition and knocking, perform combustion control to reduce the oxygen concentration of the supply air with a large amount of EGR, or lower the temperature of the compressed air (mixed gas of EGR gas and air) in the engine cylinder Therefore, there is no choice but to perform combustion control that suppresses the combustion reaction rate. The EGR performed for reducing the supply oxygen concentration has an insufficient theoretical air amount when the excess air ratio λ is less than 1.0. When the theoretical air amount is insufficient, a large amount of soot is generated even in the PCI combustion method. When the excess air ratio λ at which this soot is generated becomes the theoretical limit of the PCI combustion system. In order to lower the temperature of the compressed air (mixed gas of EGR gas and air) in the engine cylinder, it is effective to lower the compression ratio. However, lowering the compression ratio causes deterioration of startability and theoretical thermal efficiency. Arise.

  Next, it is assumed that the HPPEGR method and the PCI combustion method are combined. In the HPEGR system, the efficiency of the turbocharger is low in the light load region, so that the internal pressure of the exhaust manifold is sufficiently higher than the supercharging pressure, and EGR in the light load region is easy to perform. In a multi-stage turbo system in which turbochargers are provided in multiple stages and the turbocharger is switched according to the engine load, such as a turbocharger used in a light load area and a turbocharger used in a high load area, the light load area By using a small-capacity turbocharger, it is possible to increase the supercharging rate even in light load areas. Therefore, the supercharging ratio can be increased even in a light load region where early injection is performed by the PCI combustion method, and the excess air ratio λ can be maintained high even when a large amount of EGR is performed. As a result, early injection can be performed in a wider load region. That is, an engine load region (hereinafter referred to as a PCI region) in which the PCI combustion method can be performed is expanded.

  However, when the engine load increases, the PCI region shifts to the conventional combustion region (the load region where only the conventional combustion method can be used). When moving from the PCI region to the conventional combustion region, the amount of exhaust gas that drives the turbine increases rapidly because the EGR amount decreases. As a result, in a small capacity turbocharger with a small gas flow rate, the internal pressure of the exhaust manifold becomes much higher than the supercharging pressure, and the pumping loss increases. In the HPEGR system, no matter how high the cooling capacity of the EGR cooler that cools the EGR gas is, the cooling medium of the EGR cooler is engine cooling water, so that it cannot be cooled below the temperature of the engine cooling water. For example, the temperature of the EGR gas that has passed through the EGR cooler is around 80 ° C. Since fresh air and EGR gas are mixed in the intake manifold, the temperature of the intake gas (mixed gas of fresh air and EGR gas) in the intake manifold becomes relatively high. The temperature is 50-60 degreeC, for example. Thus, since the in-cylinder compressed gas temperature increases, the PCI region does not expand as the excess air ratio λ increases.

  Next, it is assumed that the LPEGR method and the PCI combustion method are combined. If the same small capacity turbocharger as that used in the HPEGR system is used in the LPEGR system, the entire amount of exhaust gas will pass through the turbine. For this reason, the amount of work that can be performed by the turbocharger is increased as compared with the HPEGR system, and the amount of gas (mixed gas of fresh air and EGR gas) supplied into the engine cylinder is increased. As a result, when the intake oxygen concentration after mixing the EGR gas is the same, the excess air ratio λ can be increased as compared with the HPEGR method, and expansion of the PCI region can be expected. In addition, since the mixed gas in which fresh air and EGR gas are mixed upstream of the compressor passes through the compressor and is cooled by an intercooler (not shown), the temperature of the intake gas in the intake manifold is changed to the HPPEG system. Compared to the HPPEG system, the expansion of the PCI area can be expected.

  However, if the same small-capacity turbocharger as that used in the HPEGR method is used in the LPEGR method, the allowable rotation speed of the turbocharger is reached when the engine load is lower. Therefore, in order to use the turbocharger up to the same engine load as the HPEGR system, the capacity of the turbocharger must be increased. When the capacity of the turbocharger is increased, the supercharging rate at a light engine load decreases. For this reason, the PCI area does not expand as much as expected. Moreover, since the work of the turbine and the compressor is larger than that of the HPPEG system, the pumping loss is large in both the conventional combustion region and the PCI combustion region. Further, in the conventional combustion region, the gas passages of the compressor blades and the intercooler are contaminated, and the deterioration of the compressor efficiency and the cooling capacity of the intercooler occur as aging.

  As described above, any combination has a problem.

  As a combination of the EGR method and the turbo method, an effective exhaust gas purification is a combination of a small capacity turbocharger and LPEGR method when the engine load is light, and a medium capacity turbo when the engine load is medium load. A combination of a charger and an LPEGR method or an HPEGR method, and a combination of a high capacity turbocharger and an HPEGR method when the engine load is heavy. However, an engine system equipped with all necessary devices for these combinations will be equipped with three or more types of turbochargers.

  As shown in FIG. 17, the gas temperature characteristics in the intake manifold (supply air MFD in the figure) with respect to the fuel amount are plotted for the LPEGR (Low Pressure EGR) method and the HPPEG (High Pressure EGR) method. According to this graph, the gas temperature is generally higher in the HPPEG system, and the difference between the gas temperatures of both systems is particularly large when the amount of fuel is small.

  As shown in FIG. 18, PCI limits are plotted for the LPEGR method and the HPEGR method on a state plane in which the engine speed and the fuel amount are orthogonal two axes. The PCI limit means that when the engine load indicated by the engine speed and the fuel amount is below the line indicating the PCI limit in the graph of FIG. 18, no soot is generated in the PCI combustion method, and the engine speed and the fuel amount. When the engine load indicated by is above the line indicating the PCI limit, it means that soot is generated in the PCI combustion method. In FIG. 18, the area below the line indicating the PCI limit is the PCI area (load area where the PCI combustion method can be performed).

  According to this graph, the fuel amount at which the LPEGR method has a PCI limit is higher than the HPEGR method at all engine speeds. Since the region below the line indicating the PCI limit is the PCI region, it can be seen that the LPEGR method has a wider PCI region than the HPEGR method and can perform the PCI combustion method even when the amount of fuel is relatively large.

  Next, a combination of two types of EGR devices and switching the EGR device depending on the engine load will be considered. The conventional engine systems shown in FIGS. 15 and 16 are both engine systems equipped with two types of turbochargers. An engine system having such a two-stage turbo system is equipped with an LPEGR EGR device and an HPEGR EGR device. When the engine load is light to medium load, it operates with a combination of small capacity turbocharger and LPEGR system, and when the engine load is medium load to high load, it operates with combination of large capacity turbocharger and HPPEG system And At this time, the PCI limit is included in the region where the engine load in the engine state plane is from light load to medium load.

  In this combination, in the light load region where the PCI combustion method is performed, the supercharge work of the turbocharger is increased as compared with the HPEGR method by the LPEGR method, and the PCI region is expanded by lowering the gas temperature in the intake manifold. In the medium to high load region, the capacity ratio between the small-capacity turbocharger and the large-capacity turbocharger can be made closer by suppressing the linear increase of the supply gas amount (fresh air and EGR gas) by the HPEGR method. As a result, the level difference of the supercharging pressure generated at the time of switching can be reduced, so that both turbochargers can be switched smoothly. In addition, the combustion pressure (Pmax) can be lowered by reducing the amount of gas supplied in the high load region.

  However, in this combination, the amount of gas passing through the turbocharger is different between the LPEGR method and the HPEGR method, so that a situation occurs in which the EGR amount at the time of switching the EGR method is larger or smaller than the intended EGR amount. That is, at the moment when the EGR system changes at the same engine load, the intake composition and / or intake amount will differ if the supercharging pressure is the same. If the intake air amount is the same, the supercharging pressure and the turbine inlet pressure will be different, so that a large change in pumping loss hinders smooth switching of shaft output. Thereby, a step is generated in the shaft output at the moment when the EGR system is switched.

  Therefore, an object of the present invention is to provide an engine system that solves the above-described problems and facilitates changes in various states due to switching of the EGR system.

  In order to achieve the above object, the present invention provides a high pressure EGR means for recirculating exhaust gas from an engine exhaust manifold to an intake manifold, a low pressure EGR means for recirculating exhaust gas from an exhaust gas discharge pipe to an intake pipe, and an engine load. Accordingly, it is determined whether to operate only the low-pressure EGR means, only the high-pressure EGR means, or both the low-pressure EGR means and the high-pressure EGR means, and the low-pressure EGR means and the high-pressure EGR means. And a computer for controlling the LPEGR region in which only the low-pressure EGR means is allowed to operate on the engine state plane having the engine rotational speed and the fuel amount as two orthogonal axes, and only the high-pressure EGR means being operated. An allowed HPEGR region, and either one of the low pressure EGR means and the high pressure EGR means operating or Square operating is defined and transition regions can, the computer, by the current engine rotational speed and the fuel quantity by referring to the engine state plane, is what determines the EGR means to operate.

  A turbocharger capable of switching between small capacity driving and large capacity driving is provided, and the computer switches the turbocharger to small capacity driving when operating only the low pressure EGR means, and operates only the high pressure EGR means. The turbocharger may be switched to large capacity driving.

  The engine is an engine capable of early fuel injection by a PCI combustion method, and the engine state plane of the computer defines a PCI region where fuel early injection is performed and a non-PCI region where fuel early injection is not performed, The PCI area may be included in the LPEGR area.

  In the engine state plane of the computer, an EGR boundary line that defines a low pressure EGR recommended area where the operation of the low pressure EGR means is desirable and a high pressure EGR recommended area where the operation of the high pressure EGR means is desirable is defined. A region separated by a predetermined distance or more on the low pressure EGR recommended region side is defined as the LPEGR region, a region separated from the EGR boundary line by a predetermined distance or more on the high pressure EGR recommended region side is defined as the HPEGR region, and the EGR boundary An area that is less than a predetermined distance from the line may be defined as the transition area.

  The computer predicts the future engine rotation speed and fuel amount in the engine state plane from the current engine rotation speed, the fuel amount and the past engine rotation speed and the fuel amount, and the computer predicts the past engine rotation speed, When the fuel amount is in the LPEGR region or the HPEGR region, and the current engine speed and fuel amount move to the transition region, the predicted engine speed and fuel amount exceed the EGR boundary line and other EGR If it does not move to the recommended region side, the EGR means to be operated is maintained as it is in the past, and if the predicted engine rotation speed and fuel amount exceed the EGR boundary line and move to another EGR recommended region side, the low pressure EGR means And the operation of both the high pressure EGR means.

  The computer includes the normalized rotational speed obtained by dividing the engine rotational speed by the maximum rotational speed of the EGR boundary line and the normalized fuel amount obtained by dividing the fuel amount by the fuel amount at the engine rotational speed of the EGR boundary line = 0. An engine state plane may be defined, and the EGR boundary may be defined by a function of a fourth order or less such as a circle or a straight line.

  In the computer, a lower limit boundary that is a boundary between the LPEGR region and the transition region is defined by a line whose normalized rotational speed and normalized fuel amount are smaller than the EGR boundary line by a predetermined ratio. The upper limit boundary line that is a boundary with the HPEGR region may be defined by a line that has a normalized rotational speed and a normalized fuel amount larger than the EGR boundary line by a predetermined ratio.

  In the computer, for each location on the engine state plane in which the engine rotation speed and the fuel amount are orthogonal two axes, a mixed gas amount obtained by adding the EGR amount to the air amount when EGR is not performed is defined. A function of MAF control that determines an EGR amount by referring to the engine state plane based on the engine rotation speed and the fuel amount, and the computer applies the MAF control to the low-pressure EGR means in the LPEGR region, In the HPEGR region, the MAF control may be applied to the high-pressure EGR unit, and in the transition region, the MAF control may be applied to one EGR unit and the opening degree of the other EGR unit may be gradually decreased.

  The present invention exhibits the following excellent effects.

  (1) Various states can be changed smoothly by switching the EGR method.

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

  As shown in FIG. 1, an engine system 1 according to the present invention includes a high-pressure stage turbocharger 5 in which exhaust gas extracted from an exhaust manifold 3 of an engine 2 is supplied to a turbine 4, and a turbine 4 of the high-pressure stage turbocharger 5. A high-pressure exhaust regulating valve 6 that regulates the exhaust that exits, and an exhaust switching valve that switches between exhaust that exits from the turbine 4 of the high-pressure stage turbocharger 5 and exhaust that branches off from the exhaust manifold 3 and supplies it to the turbine 8 of the low-pressure stage turbocharger 7. 9, a low pressure stage turbocharger 7 in which the turbine 8 is driven by exhaust gas supplied from the exhaust gas switching valve 9, an exhaust gas exhaust pipe 10 connecting the outlet of the turbine 8 of the low pressure stage turbocharger 7 to the atmosphere, and exhaust gas A DPF 11 inserted into the exhaust pipe 10 to remove particulate matter from the exhaust gas, and inserted into the exhaust gas exhaust pipe 10. NOx catalytic nitrogen oxide removing device 12 for removing nitrogen oxides from exhaust gas, high pressure EGR pipe 14 for taking exhaust gas as EGR gas from exhaust manifold 3 of engine 2 and sending it to intake manifold 13 of engine 2; A high pressure EGR cooler 15 inserted into the high pressure EGR pipe 14, a high pressure EGR valve 16 for adjusting the amount of EGR gas in the high pressure EGR pipe 14, and exhaust gas after passing through the DPF 11 from the exhaust gas discharge pipe 10 as EGR gas. The branching low pressure EGR pipe 17, the low pressure EGR cooler 18 inserted in the low pressure EGR pipe 17, the low pressure EGR valve 19 for adjusting the amount of EGR gas in the low pressure EGR pipe 17, and the compressor of the low pressure stage turbocharger 7 from the atmosphere Low pressure EGR piping 17 joins on the way The intake pipe 21, the intake throttle 22 inserted to the atmosphere side from the low-pressure EGR pipe joining point of the intake pipe 21, and the output of the compressor 20 of the low-pressure stage turbocharger 7 are input to the compressor 23 of the high-pressure stage turbocharger 5. A low-pressure turbo output gas pipe 24 connected to the intake port, an intake switching valve 25 for switching the output of the compressor 23 of the high-pressure turbocharger 5 and the output of the compressor 20 of the low-pressure turbocharger 7, and the gas selected by the intake switching valve 25 And a high-pressure gas pipe 26 provided to the intake manifold 13 of the engine 2.

  The engine system 1 is controlled by the computer 27. The computer 27 can input signals necessary for EGR control, such as an engine speed, an engine air amount, and an engine fuel amount (also simply referred to as a fuel amount), from a sensor (not shown). The computer 27 repeatedly samples the input signals from these sensors at an appropriate sampling time, accumulates the current signal value and the signal value for an appropriate time in the past in a memory, and uses them for calculation as needed. It has become. The computer 27 is an actuator necessary for EGR control, such as an actuator for the exhaust gas switching valve 9, an actuator for the high pressure EGR valve 16, an actuator for the low pressure EGR valve 19, an actuator for the intake air switching valve 25, and an actuator for the high pressure exhaust adjustment valve 6. A drive signal can be output.

  The high pressure EGR pipe 14 and the high pressure EGR valve 16 constitute high pressure EGR means. The low pressure EGR pipe 17 and the low pressure EGR valve 19 constitute a low pressure EGR means. As described above, the engine system 1 of the present invention includes the high pressure EGR means for returning the exhaust gas from the exhaust manifold 3 of the engine 2 to the intake manifold 13 and the low pressure EGR for returning the exhaust gas from the exhaust gas discharge pipe 10 to the intake pipe 21. Together with means.

  In the present invention, the computer 27 determines whether to operate only the low pressure EGR means, only the high pressure EGR means, or both the low pressure EGR means and the high pressure EGR means depending on the engine load. Thus, the low pressure EGR means and the high pressure EGR means are controlled.

  The computer 27 uses the engine rotation speed and the fuel amount as indexes of engine load, and selectively operates the EGR means in accordance with these indexes. That is, the computer 27 has an LPEGR region in which only the low pressure EGR means is allowed to operate, an HPEGR region in which only the high pressure EGR means is allowed to operate, and the low pressure EGR on the engine state plane having the rotation speed and the fuel amount as two orthogonal axes. A transition region in which one or both of the means and the high-pressure EGR means can be operated is defined on the memory (see FIGS. 2 to 10). The computer 27 is configured to determine the EGR means to be operated by referring to the engine state plane based on the current engine speed and fuel amount.

  The engine system 1 in FIG. 1 is a two-stage turbo system including a high-pressure stage turbocharger 5 and a low-pressure stage turbocharger 7. The engine system 1 can be switched between small-capacity driving and large-capacity driving by combining the high-pressure stage turbocharger 5 and the low-pressure stage turbocharger 7. The present invention can be implemented if a turbocharger capable of switching between small capacity driving and large capacity driving is provided regardless of the type and number of turbochargers.

  When the computer 27 operates only the low-pressure EGR means (the engine 2 has a light to medium load and corresponds to the LPEGR region), the turbocharger capable of switching between small capacity driving and large capacity driving is switched to the small capacity driving. When switching and operating only the high-pressure EGR means (the engine 2 has a medium to high load and corresponds to the HPEGR region), the program is configured to switch the turbocharger to large capacity driving.

  The engine 2 is an engine 2 capable of early fuel injection by the PCI combustion method. Therefore, the engine state plane of the computer 27 defines a PCI region where early fuel injection is performed and a non-PCI region where early fuel injection is not performed. The PCI area is completely included in the LPEGR area, and a part of the non-PCI area is included in the LPEGR area (see FIGS. 2 to 4).

  The engine state plane defined on the memory of the computer 27 defines an EGR boundary line that divides a low pressure EGR recommended region where the operation of the low pressure EGR means is desirable and a high pressure EGR recommended region where the operation of the high pressure EGR means is desirable. An area that is more than a predetermined distance away from the EGR boundary line toward the recommended low-pressure EGR area is defined as an LPEGR area. An area that is more than a predetermined distance away from the EGR boundary line toward the high-pressure EGR recommended area side is defined as an HPEGR area. A region less than a predetermined distance from the EGR boundary is defined as a transition region (see FIGS. 4 to 10).

  In the engine system 1 of FIG. 1, the engine 2 including the PCI region is a light to medium load LPEGR region, the turbocharger is a small capacity drive and the EGR method is the LPEGR method, and the engine 2 is a medium to high load HPEGR region. The turbocharger operates with a large capacity drive and the EGR system operates in combination with the HPPEG system. A transition region is provided near the EGR boundary between the LPEGR region and the HPEGR region. In the transition region, an algorithm for obtaining smooth changes in various states is executed when the EGR method is switched.

  The computer 27 is configured to predict a future engine speed and fuel amount in the engine state plane from the current engine speed, fuel amount, past engine speed, and fuel amount. Further, the computer 27 has a past engine rotational speed and fuel amount in the LPEGR region or the HPPEG region, and when the current engine rotational speed and fuel amount move to the transition region, the predicted engine rotational speed and fuel amount are at the EGR boundary. If it does not move to another EGR recommended area side beyond the line, the EGR means to be operated is maintained as it was in the past, and the predicted engine speed and fuel amount can move to the other EGR recommended area side beyond the EGR boundary line. For example, the program is configured to start the operation of both the low pressure EGR means and the high pressure EGR means.

  Further, in the memory of the computer 27, the normalized fuel amount obtained by dividing the engine speed and the fuel amount by dividing the engine speed by the maximum engine speed of the EGR boundary line by the fuel amount at the engine speed of the EGR boundary line = 0. And the engine state plane is defined (see FIGS. 3 to 10). The EGR boundary line is preferably defined by a function of a fourth order or less such as a circle or a straight line.

  In the memory of the computer 27, the lower limit boundary line that is the boundary between the LPEGR region and the transition region is defined by a line whose normalized rotational speed and normalized fuel amount are smaller than the EGR boundary line by a predetermined ratio. In this memory, the upper limit boundary line that is the boundary between the transition region and the HPPEG region is defined by a line having a normalized rotational speed and a normalized fuel amount larger than the EGR boundary line by a predetermined ratio (FIGS. 4 to 10). reference).

  In the memory of the computer 27, the amount of mixed gas obtained by adding the EGR amount to the air amount when EGR is not performed is defined for each location on the engine state plane in which the engine rotation speed and the fuel amount are two orthogonal axes. However, this is not shown. The computer 27 has a function of MAF control for determining the EGR amount by referring to the engine state plane based on the current engine speed and fuel amount. In the present invention, the computer 27 applies MAF control to the low pressure EGR means in the LPEGR region, applies MAF control to the high pressure EGR means in the HPEGR region, and applies MAF control to one EGR means in the transition region. On the other hand, the other EGR means is configured such that the opening degree is gradually reduced.

  Hereinafter, the operation and principle of the present invention will be described in detail.

  As shown in FIG. 2, in the engine system 1 of the present invention, an engine state plane having an engine rotation speed N and a fuel amount Q as two orthogonal axes is defined for use in determining whether to switch the EGR method. The The engine state plane is desirably represented by a map that can be searched on the memory using the engine speed N and the fuel amount Q as parameters. A curve such as a boundary line drawn on the engine state plane may be defined by a function. Hereinafter, the engine state plane as shown in FIG. 2 is referred to as a region map.

  In addition to the area map, the engine system 1 has conventionally defined a mixed gas amount for each location on the engine state plane having the engine rotational speed and the fuel amount as two orthogonal axes for use in MAF control. Yes. Hereinafter, this MAF control engine state plane (not shown) is referred to as an EGR map.

In the region map of FIG. 2, the horizontal axis represents the engine speed N (rpm), the vertical axis represents the fuel amount Q (mm ³ / st), and the low pressure EGR recommended region where the operation of the low pressure EGR means is desirable and the high pressure EGR described above. This defines an EGR boundary line BL that defines a high pressure EGR recommended region where the operation of the means is desirable.

  The PCI limit PL is shown in the area map of FIG. This will be described with reference to FIG.

  As shown in FIG. 3, the engine speed N divided by the maximum rotation speed Nmax of the EGR boundary line BL, which is the maximum rotation speed in the low pressure EGR recommended region, is a normalized rotation speed N *, and the fuel amount Q is a low pressure. The normalized fuel amount Q * is obtained by dividing the EGR boundary line BL, which is the maximum fuel amount in the EGR recommended region, by the fuel amount Qmax at the engine rotation speed = 0. An engine state plane (region map) is defined with the normalized rotational speed N * and the normalized fuel amount Q * as two orthogonal axes. In the region map of FIG. 3, the horizontal axis is the engine speed N * (no unit), the vertical axis is the fuel amount Q * (no unit), and the EGR boundary line BL has coordinates (1, 0) and coordinates (0, 1). )

For example, the EGR boundary line BL is
a1 × Q * ⁴ + a2 × Q * ³
+ A3 × Q * ² + a4 × Q * + a5
= B1 x N * ⁴ + b2 x N * ³
+ B3 × N * ² + b4 × N * + b5 (1)
a1 to a5 and b1 to b5 are defined by approximate expressions called constants. As the approximate expression, a linear function, a quadratic function, a cubic function, a quartic function, a circular function, an elliptic function, or the like can be used. As will be described later, when the control is shifted from one EGR method to another EGR method, the coordinates reaching the EGR boundary after entering the transition region are predicted by calculation. At this time, it is desirable to employ a function of the fourth order or lower that can obtain a general algebraic solution as the solution of the equation.

  An upper limit boundary line UB and a lower limit boundary line DB of the transition region are defined. FIG. 4 shows only the definition of the lower limit boundary line DB. The upper limit boundary line UB is a boundary line that enters the engine state in the transition region from the engine state in which only the high-pressure EGR means is allowed to operate. The lower limit boundary line DB is a boundary line that enters the engine state in the transition region from the engine state in which only the low pressure EGR means is allowed to operate. The upper right boundary UB and the right are HPEGR areas, the lower limit boundary DB and the left are LPEGR areas, and the area between the upper limit boundary UB and the lower limit boundary DB is a transition area. The upper limit boundary line UB and the lower limit boundary line DB may be defined by the approximate expression as described above.

  The lower limit boundary DB is defined by a line in which the normalized rotational speed N * and the normalized fuel amount Q * are smaller than the EGR boundary line BL by a predetermined ratio. The upper limit boundary line UB is defined by a line in which the normalized rotational speed N * and the normalized fuel amount Q * are larger than the EGR boundary line BL by a predetermined ratio. For example, if the range of ± 5% of the EGR boundary line BL is a transition region, the upper limit boundary line UB is obtained from each coordinate of the EGR boundary line BL × 1.05, and the lower limit boundary line DB is each coordinate of the EGR boundary line BL. X 0.95. In the following description, it is assumed that the upper limit boundary UB and the lower limit boundary DB are defined at ± 5% of the coordinates of the EGR boundary line BL.

  In the engine system 1, it is desirable that the optimum upper limit boundary line UB and lower limit boundary line DB are determined by investigation through experiments using actual machines.

In FIG.
N * ² + Q * ² = 1 (2)
An EGR boundary line BL of arc approximation defined by the above, an EGR boundary line BL obtained by actual measurement,
N * ² + Q * ² = 0.95 ² (3)
The lower limit boundary line DB defined by is shown.

  In the present invention, the PCI area is included in the LPEGR area. That is, as shown in FIG. 4, the PCI limit PL is in the LPEGR region (below and below the lower limit boundary line DB). The PCI area is below the PCI limit, and the non-PCI area is above the PCI limit.

  FIG. 5A shows an area map when the EGR boundary line BL is approximated by a straight line, and FIG. 5B shows an area map when the EGR boundary line BL is approximated by an arc. In either case, the lower limit boundary DB and the upper limit boundary UB are defined at ± 5% of the coordinates of the EGR boundary line BL, and the lower limit boundary DB, the upper limit boundary UB, and the transition region are linear or arcuate. Shape. The HPEGR region is above the right and above the upper boundary line UB, the LPEGR region is below and below the lower boundary line DB, and the transition region is between the upper boundary line UB and the lower boundary line DB. These definitions are the same as in FIGS. 2 and 3, the EGR boundary line BL divides two regions, a low pressure EGR recommended region where the operation of the low pressure EGR means is desirable and a high pressure EGR recommended region where the operation of the high pressure EGR means is desirable. However, when the EGR system is switched on the EGR boundary line BL, various engine states may change abruptly. In the present invention, as shown in FIG. 5 and subsequent figures, the LPEGR region, the transition region, and the HPEGR region are divided by the lower limit boundary line DB and the upper limit boundary line UB.

The computer 27 measures the current engine speed N and the fuel amount Q by using respective sensors, and obtains a normalized speed N * and a normalized fuel amount Q *. The value on the right side of equation (1) above,
^{a1 × Q * 4 + a2 ×} Q * 3
+ A3 × Q * ² + a4 × Q * + a5 (4)
And the value on the left side,
b1 x N * ⁴ + b2 x N * ³
+ B3 × N * ² + b4 × N * + b5 (5)
And the current EGR method is determined.

For example, if it is immediately after starting the engine, it is idling, so
a1 × Q * ⁴ + a2 × Q * ³
+ A3 × Q * ² + a4 × Q * + a5
<B1 x N * ⁴ + b2 x N * ³
+ B3 × N * ² + b4 × N * + b5 (6)
It becomes. The point E (N *, Q *) of the area map representing the engine load at this time is located in the LPEGR area as shown in the figure. Therefore, the computer 27 operates only the low pressure EGR means.

  Note that when a vertical line is made upward from the point E and intersects with the EGR boundary line BL, the normalized fuel amount Q * on the EGR boundary line BL corresponding to the normalized rotational speed N * is known from the intersection Eb.

As shown in FIGS. 6 (a) and 6 (b), it is assumed that the engine load thereafter increases and the engine speed N and the fuel amount Q increase. At this time,
(A1 × Q * ⁴ + a2 × Q * ³
+ A3 × Q * ² + a4 × Q * + a5) _0.95
^{= (B1 × N * 4 +} b2 × N * 3
+ B3 × N * ² + b4 × N * + b5) _0.95 (7)
Suppose that The subscript 0.95 in Equation (7) indicates that the engine load has reached the lower limit boundary line DB. A subscript of 1.05 indicates that the engine load is on the upper limit boundary line UB.

  When the engine load reaches the relationship of Expression (7), the normalized rotational speed is N0 *, the normalized fuel amount is Q0 *, and a point E0 is shown in the region map. The normalized rotational speed immediately before the engine load reaches the relationship of Expression (7) is Nm *, the normalized fuel amount is Qm *, and a point Em is shown in the region map. The computer 27 solves the equation of the straight line passing through the points Em and E0 and the EGR boundary line BL, and obtains a point E1 (N1 *, Q1 *) at which the two intersect as a future prediction point. A point E1 on the region map represents a point where the locus of the point representing the engine load reaches the EGR boundary line BL. At this time, the prediction that the engine load will reach the EGR boundary line BL in the future is established. Therefore, the computer 27 starts operation of both the low pressure EGR means and the high pressure EGR means.

  On the other hand, the equation of the straight line passing through the points Em and E0 and the EGR boundary line BL may not have a real root. Further, the solution (N1 *, Q1 *) may not satisfy 1> N1 *> 0 and 1> Q1 *> 0. This is a solution that is impossible for a real engine. In these cases, the prediction that the engine load will not reach the EGR boundary line BL in the future is established. Therefore, the computer 27 maintains the EGR means to be operated as it was in the past. As shown in FIG. 6, when only the low pressure EGR means has been operated in the past, the operation of only the low pressure EGR means is maintained.

  As shown in FIG. 7A and FIG. 7B, it is assumed that the engine load is lightened from the high load and exceeds the upper limit boundary line UB. An area map point Em (Nm *, Qm *) representing the previous past engine load is located in the HPPEG area, and the computer 27 operates only the high-pressure EGR means. The current engine load is the point E0 (N0 *, Q0 *) of the upper limit boundary UB. The computer 27 solves the equation of the straight line passing through the points Em and E0 and the EGR boundary line BL and obtains a point E1 (N1 *, Q1 *) where the two intersect. If it is predicted that the engine load will reach the EGR boundary line BL in the future, the computer 27 starts operation of both the low pressure EGR means and the high pressure EGR means.

  As shown in FIG. 8A, the point Em (Nm *, Qm *) of the region map representing the previous past engine load is located in the HPPEG region, and the computer 27 operates only the high-pressure EGR means. Assume that the engine load becomes lighter and reaches the point E0 (N0 *, Q0 *) of the upper limit boundary line UB. The computer 27 solves the equation of the straight line passing through the points Em and E0 and the EGR boundary line BL to obtain a point E1 (N1 *, Q1 *) where the two intersect, but the equation does not have a real root. That is, the straight line passing through the point Em and the point E0 does not intersect the EGR boundary line BL. At this time, the computer 27 keeps operating only the high-pressure EGR means.

  As shown in FIG. 8B, the area map point Em (Nm *, Qm *) representing the previous past engine load is located in the HPPEG area, and the computer 27 operates only the high-pressure EGR means. Assume that the engine load becomes lighter and reaches the point E0 (N0 *, Q0 *) of the upper limit boundary line UB. The computer 27 solves the equation of the straight line passing through the point Em and the point E0 and the EGR boundary line BL and obtains a point E1 (N1 *, Q1 *) where the two intersect, but this is not possible in the actual engine (in this example) Since the fuel amount is negative), the computer 27 keeps operating only the high-pressure EGR means.

  Lower limit boundary DB when engine load reaches point E0 (N0 *, Q0 *) of upper limit boundary UB when load decreases from high load to light load, or when engine load increases from light load to high load When the point E0 (N0 *, Q0 *) is reached, the computer 27 opens the opening of the EGR valve (the high pressure EGR valve 16 when the load is reduced in the HPPEG region and the low pressure EGR valve 19 when the load is increased in the LPEGR region). Store as a fixed value. Further, the computer 27 sets the opening degree (same as above) of the EGR valve at the predicted point E1 (N1 *, Q1 *) to 0. The computer 27 linearly interpolates the opening degree of the EGR valve during the transition from the point E0 to the point E1 with respect to the normalized rotational speed N *. That is, control is performed so that the opening degree of the EGR valve linearly decreases from the stored fixed value to 0.

  As shown in FIG. 9, when the engine load is reduced from a high load to a light load (that is, when only the high-pressure EGR means is operating), the current point E0 from the previous past point Em on the area map. When reaching the value, the operation of both the low pressure EGR means and the high pressure EGR means is started. At this time, the computer 27 controls the high pressure EGR valve 16 of the high pressure EGR means from the point E0 to the predicted point E1 with the opening obtained by the linear interpolation. During this time, the computer 27 controls the low pressure EGR valve 19 of the low pressure EGR means by MAF control. Thereby, when the engine load actually passes through the point E1, the opening degree of the high pressure EGR valve 16 of the high pressure EGR means becomes 0. Therefore, from the point E0 entering the transition region from the HPEGR region, the transition region is shifted to the LPEGR region. The switching of the EGR method up to the point E2 to enter becomes smooth.

  As shown in FIG. 10, when the engine load is increased from a light load to a high load (that is, when only the low pressure EGR means is operating), the current point E0 from the previous past point Em on the area map. When reaching the value, the operation of both the low pressure EGR means and the high pressure EGR means is started. At this time, the computer 27 controls the low pressure EGR valve 19 of the low pressure EGR means from the point E0 to the predicted point E1 with the opening obtained by the linear interpolation. During this time, the computer 27 controls the high pressure EGR valve 16 of the high pressure EGR means by MAF control. Thereby, when the engine load actually passes through the point E1, the opening degree of the low pressure EGR valve 19 of the low pressure EGR means becomes 0. Therefore, from the point E0 entering the transition region from the LPEGR region, the transition region is changed to the HPEGR region. The switching of the EGR method up to the point E2 to enter becomes smooth.

  An opening smaller than the opening obtained by the linear interpolation may be set as an instruction opening to the low pressure EGR means or the high pressure EGR means by multiplying the opening obtained by the linear interpolation by a constant A or B smaller than 1. Thereby, the opening degree of the EGR means in the transition region can be made different from the opening degree obtained by the linear interpolation. You may make it change arbitrarily the share ratio of the EGR amount (EGR rate) between the said EGR means and the other EGR means under MAF control.

  As described above, according to the present invention, in an engine system equipped with one or more turbochargers, when a plurality of EGR means are switched according to the engine state indicated by the engine speed and the fuel amount, A transition region having a finite width is defined on the boundary line between a region where the means is recommended and a region where other EGR means are recommended. In the transition region, a plurality of EGR methods are used in combination, stepwise or steplessly. Therefore, the recommended EGR means is switched to only the recommended EGR means when exiting the transition area. As a result, sudden changes in the intake air amount and exhaust gas amount due to differences in EGR methods can be mitigated, and changes in various states accompanying the switching of the EGR means become smooth. As a result, generation of harmful exhaust gas can be suppressed, and unintended deterioration of fuel consumption can be suppressed. Also, the PCI area for early fuel injection is included in the LPEGR area, and the HPEGR area is at a higher engine load than the LPEGR area. Can be prevented and secular change of the air supply system can be suppressed.

  11 and 12 show a control flow in the engine system 1 of the present invention. However, the control related to PCI and the switching control between small capacity driving and large capacity driving of the turbocharger are omitted.

  In the following description and flowchart, according to the convention of computer control procedure description, the step equation (=) indicated by a rectangular box means that the value of the right side is substituted for the left side, and the step indicated by the diamond box etc. Expressions and inequalities mean determination of whether the right side value and left side value match or not.

  Step S1. The vehicle key switch is turned on by the driver. As a result, the control power supply in the vehicle is turned on, the computer 27 is activated, and the computer 27 starts executing the following steps.

Step S2. Variables Q1 *, N1 *, I, K, J, H, J *, and H * are set to 0, respectively. The variable Q1 * is the normalized fuel amount, N1 * is the normalized rotational speed, I, K, J, H, J *, and H * are all for flow control that occurs when the engine state transitions between the regions. It is a binary variable (so-called flag). The variable I is flagged as I = 1 when it first enters the transition region. The variable K is flagged as K = 1 when in the transition region. When the variable combination (J *, H *) is (1, 0), it is in the LPEGR area (Q * <F _0.95 (N *) area described later) or the transition area (described later) after passing through the LPEGR area. F _1.05 (N *)> Q *> F _0.95 (N *)). When (J *, H *) is (0, 1), it means that it is in the HPEGR area (Q *> F _1.05 (N *) described later) or has entered the transition area after passing through the HPEGR area.

  Step S3. Various maps necessary for engine control and EGR control of the present invention are read.

  Step S4. The engine is started based on the driver's starting operation.

Step S5. Engine rotational speed N (rpm) by the sensors, charged fuel quantity Q (mm ³ / st), reads the intake air quantity MAF (g / cyl).

  Step S6. The engine rotational speed N read in step S5 is divided by the maximum rotational speed Nmax in the low pressure EGR recommended region to be normalized rotational speed N *, and the input fuel amount Q is divided by the maximum fuel amount Qmax in the low pressure EGR recommended region to The quantity is Q *.

Step S7. A function F (x) that approximates the EGR boundary line BL, a function F _0.95 (x) that approximates the lower limit boundary line DB, and a normalized rotation speed N * for x of the function F _1.05 (x) that approximates the upper limit boundary line UB. The values of these functions are obtained and compared with the normalized fuel amount Q *. If Q * <F _0.95 (N *), the process proceeds to step S7-1. Otherwise, the process proceeds to step S9.

  Step S7-1. The engine load is in the LPEGR region. J = 1 and H = 0 are substituted, and the values of J and H are substituted for J * and H *. Note that the determination in step S7 is always YES immediately after the engine is started, and J = 1 and H = 0 in step S7-1.

  Step S8. Since the engine load is in the LPEGR region, only the low pressure EGR means is operated.

  Step S8-1. The opening degree of the high pressure EGR valve 16 of the high pressure EGR means is fixed to zero.

  Step S8-2. In step S5, the opening degree of the low pressure EGR valve 19 of the low pressure EGR means is controlled so that the intake air amount MAF read from the sensor becomes MAF0 defined by the EGR map. Proceed to step S23.

Step S9. If F (N *)> Q *> F _0.95 (N *), the process proceeds to step S10. Otherwise, the process proceeds to step S13.

Step S10. The engine load is closer to the lower limit boundary line DB than the EGR boundary line BL in the transition region. When this region is first reached, the variable J * is a value immediately before Q *> F _0.95 (N *), that is, J * = 1 substituted in step S7-1. Therefore, the combination of variables (J *, H *, K, I) is (1, 0, 0, 0). This means that the engine load has entered the transition region from the LPEGR region. In step S10, it is determined whether (J *, H *, K, I) is (1, 0, 0, 0). If YES, the process proceeds to step S12. From step S12, the process proceeds to step S30. The EGR control procedure in the transition area performed after step S30 will be described in detail later. However, in the case of showing only the flag and the flow, in step S30, I = 1 and K = 1. After the EGR control in step S5, the process returns to step S5. If NO in step S10, the process proceeds to step S11.

  Step S11. It is determined whether (J *, H *, K, I) is (1, 0, 1, 1). If YES, the process proceeds to step S12. If NO, the process proceeds to step S7-1.

Step S13. If F _1.05 (N *)> Q *> F (N *), the process proceeds to step S14. Otherwise, the process proceeds to step S18.

  Step S14. It is determined whether (J *, H *, K, I) is (1, 0, 0, 0). If YES, the process proceeds to step S20. If NO, the process proceeds to step S15.

  Step S15. It is determined whether (J *, H *, K, I) is (0, 1, 0, 0). If YES, the process proceeds to step S12. If NO, the process proceeds to step S16.

  Step S16. It is determined whether (J *, H *, K, I) is (0, 1, 1, 1). If YES, the process proceeds to step S12. If NO, the process proceeds to step S17. From step S17, the process returns to step S5.

  In step S9 to step S11 and step S13 to step S16, it means that the engine load is in the transition region. When the engine load increases from the light load and reaches the EGR boundary line BL, Q * ≈F (N *), which is determined in step S30. Thereafter, when K = 0 and I = 0 are substituted in step S30-2, (J *, H *, K, I) becomes (1, 0, 0, 0). Thus, when the engine load increases from the light load and reaches the EGR boundary line BL, the EGR control procedure after step S20 is executed.

Step S18. The engine load increased and Q *> F _1.05 (N *). That is, the engine load is in the HPPEG region. Substitute H = 1 and J = 0 and proceed to step S19.

  Step S19. Substitute the current values of J and H (0, 1) for J * and H *, and proceed to step S20.

  Step S20. Since the engine load is in the HPEGR region, only the high pressure EGR means is operated.

  Step S20-1. The opening of the low pressure EGR valve 19 of the low pressure EGR means is fixed to zero.

  Step S20-2. In step S5, the opening degree of the high pressure EGR valve 16 of the high pressure EGR means is controlled so that the intake air amount MAF read from the sensor becomes MAF0 defined by the EGR map. Proceed to step S23.

  Step S23. After substituting the current N * for the past normalized rotational speed Nm * and substituting the current Q * for the past normalized fuel amount Qm *, the process returns to step S5.

When the engine load is decreasing and the flow comes from step S5 to step S13, (J *, H *, K, I) is (0, 1, 0, 0). In this case, the process does not proceed to step S20, but proceeds to step S30 through step S12. Further, when the flow from Step S5 through Step S30 and the subsequent steps comes to Step S13, (J *, H *, K, I) is (0, 1, 1, 1). In this case, the flow of step S13 → step S14 → step S15 → step S16 → step S30 is repeated until the engine load decreases and F (N *)> Q *> F _0.95 (N *) is satisfied.

  Step S30. The execution of the EGR control procedure in the transition area is started.

  Step S30-1. The absolute value of the difference between Q1 * and F (N *) is compared with a predetermined allowable value Δ. In other words, it is determined whether or not Q1 * ≈F (N *). If YES, the process proceeds to step S30-2. If NO, the process proceeds to step S30-3.

  Step S30-2. Substituting I = 0, K = 0, H = 0 and setting variable Q1 * = 0. Proceeding to step S31, the process returns from step S31 to step S5.

  Step S30-3. Set K = 1 and proceed to subroutine A (FIG. 12).

The meaning after step S30 will be explained. When the engine load is F (N *)> Q *> F _0.95 (N *), (J *, H *, K, I) is (1, 0, 0, 0) or (1, 0, 1, 1), the EGR control procedure in this transition region is started. When the engine load is F _1.05 (N *)> Q *> F _0.95 (N *), (J *, H *, K, I) is (0, 1, 0, 0) or (0 , 1, 1, 1), the EGR control procedure in this transition region is started.

  In step S30-1, when the engine load changes and the future of the locus on the area map is predicted, it is determined whether or not the EGR boundary line BL is reached. Q1 * is a predicted point of the normalized fuel amount Q * at the normalized rotational speed N *. F (N *) is a point on the EGR boundary line BL at the normalized rotational speed N * (intersection Eb in FIGS. 5A and 5B). When the absolute value of the difference between the two is less than Δ, which is a minute value, it can be determined that the predicted point has reached the EGR boundary line BL. Therefore, it will progress to step S30-2. Thereafter, the EGR method is switched regardless of the area. In step S30-2, variables J *, H *, K, I, and Q1 * are all set to zero.

  If it is determined that the predicted point has not reached the EGR boundary line BL, the process proceeds to step S30-3, 1 is substituted into the variable K, the process proceeds to subroutine A, and the EGR control procedure in the transition region is continued. . Note that an approximate solution of a function is used as an arithmetic expression for performing prediction.

When the engine load decreases and Q * ≈F (N *), since I = 0 and K = 0 are substituted in step S30-2, (J *, H *, K, I) is ( 0, 1, 0, 0), the flow returns to step S5. If the engine load further decreases from that state and F (N *)> Q *> F _0.95 (N *), (J *, H *, K, I) is (0, 1, 0, 0). Since there is, step S9-> step S10-> step S11-> step S7-1 will flow. Therefore, MAF control of the low pressure EGR means is performed when the engine load is in the transition region.

When the engine load further decreases and Q * <F _0.95 (N *), the flow from step S5 flows from step S7 to step S7-1. Substitution of J = 1, H = 0, J * = J, H * = H is performed, and the combination of variables (J *, H *) = (1, 0), and MAF control of the low pressure EGR means is performed. It will be. The variable combination (J *, H *, K, I) returns immediately after the engine is started. Thereafter, the EGR control as described above is repeated.

  Step S40-1 of subroutine A (FIG. 12 from here). It is determined whether I = 1. If YES, the process proceeds to step S40-9. If NO, the process proceeds to step S40-2. When entering the EGR control procedure in the transition region for the first time, I = 0.

  Step S40-2. The opening LA0 of the low pressure EGR valve 19 and the opening HA0 of the high pressure EGR valve 16 are read. Proceed to step S40-3.

  Step S40-3. N0 * = N * is substituted, Q0 * = Q * is substituted, and I = 1 is substituted.

  Step S40-4. Normalized rotation speed Nm * immediately before the engine load enters the transition region, normalized fuel amount Qm * (point Em on the region map), normalized rotation speed N0 * when the engine load reaches the transition region, Solve the equation of the straight line passing through the normalized fuel amount Q0 * (point E0 on the region map) and the EGR boundary line BL (Q * = F (N *)) to find the point E1 (N1 *, Q1 *) where both intersect Obtained as a future prediction point. This prediction point is a prediction point at which the engine load reaches the EGR boundary line BL due to increase or decrease. Proceed to step S40-5.

  Step S40-5. In the calculation in step S40-4, when the equation does not have a real root (see FIG. 8A), it is predicted that the locus on the area map will not reach the EGR boundary line BL in the future. Therefore, in step S40-5, it is determined whether or not it has a real root. If NO (does not have a real root), the process proceeds to step S40-6. If YES, the process proceeds to step S40-8.

  Step S40-6. Substitute I = 0, K = 0, and substitute Q1 * = 0. Proceed to step S40-7. From step S40-7, the process returns to step S5 (FIG. 11).

  Step S40-8. Even if the equation has a real root in the calculation in step S40-4, it is necessary to check whether the solution (N1 *, Q1 *) is possible in the actual engine (see FIG. 8B). Therefore, in step S40-8, it is determined whether 0 <N1 * <1 and 0 <Q1 * <1. If no, the process proceeds to step S40-6. If YES, the process proceeds to step S40-9.

Step S40-9. If the engine state has entered the transition area, it is _{always, F 1.05 (N *)>} Q *> F 0.95 (N *). At this time, if F (N *)> Q *> F _0.95 (N *), it can be determined that the transition region has been entered from the LPEGR region. Otherwise, it can be determined that the transition region has been entered from the HPPEG region. In step S40-9, it is determined whether F (N *)> Q *> F _0.95 (N *). If YES, the process proceeds to step S40-10. If NO, the process proceeds to step S40-12.

Step S40-10. This is a case where the engine state enters the transition region from the LPEGR region. Between the predicted point E1 (N1 *, Q1 *) reaching the EGR boundary line BL calculated in step S40-4 and the entry point E0 (N0 *, Q0 *) into the transition region, the current point E (N * , Q *) is obtained by linear interpolation. The low pressure EGR valve 19 is controlled at the opening LA0. That is, in step S40-10, the EVL (actuator driving amount of the low pressure EGR valve 19) is set to
EVL = A × LA0 × (N1 * −N *) / (N1 * −N0 *)
Is assigned. Proceed to step S40-11. The positive constant A is a constant that has a value of 1 or less and adjusts the rate at which the valve is closed in the opening degree control.

  Step S40-11. The EGR amount that is insufficient in the EGR control in step S40-10 is obtained from the difference in MAF0 defined by the EGR map that is the target value with respect to the current intake air amount MAF read from the sensor in step S5, and the intake air amount MAF is calculated in the EGR map. The opening degree of the high-pressure EGR valve 16 of the high-pressure EGR means is controlled so as to be the target value MAF0 defined in (1). That is, MAF control is applied to the high pressure EGR valve 16. Subroutine A is terminated and control returns to the control flow of FIG.

Step S40-12. This is a case where the engine state enters the transition region from the HPPEG region. Between the predicted point E1 (N1 *, Q1 *) reaching the EGR boundary line BL calculated in step S40-4 and the entry point E0 (N0 *, Q0 *) into the transition region, the current point E (N * , Q *) is obtained by linear interpolation. The high pressure EGR valve 16 is controlled by the opening degree LA0. That is, in step S40-12, EVH (actuator driving amount of high pressure EGR valve 16) is set to EVH.
EVH = B × HA0 × (N1 * −N *) / (N1 * −N0 *)
Is assigned. Proceed to step S40-13. The positive constant B has a value of 1 or less, and is a constant that adjusts the rate at which the valve is tightened in the opening degree control.

  Step S40-13. The EGR amount that is insufficient in the EGR control in step S40-12 is obtained from the difference in MAF0 defined by the EGR map that is the target value with respect to the current intake air amount MAF read from the sensor in step S5, and the intake air amount MAF is obtained from the EGR map. The degree of opening of the low EGR valve 19 of the low EGR means is controlled so that the MAF0 defined by the above is satisfied. That is, MAF control is applied to the low pressure EGR valve 19. Subroutine A is terminated and control returns to the control flow of FIG.

  As shown in FIG. 11, when the flow returns from subroutine A, the flow proceeds to step S5.

  Next, FIGS. 13 and 14 show the flow of control according to another embodiment of the engine system 1 of the present invention. In this control flow, step S24 is inserted and variable I is removed in the middle from the end of subroutine A to step S5 in the control flow of FIGS. In step S24, Nm * = N * is substituted, and Qm * = Q * is substituted. The variable I is removed at every step including step S2. As a result, the prediction point (N1 *, Q1 *) is always calculated and corrected using the previous engine state, so that the prediction accuracy of the prediction point (N1 *, Q1 *) is improved.

  In the present invention, the LPEGR region, the HPPEGR region, and the transition region are defined in the engine state plane (region map), but the type division of the region may be further increased. Even in this case, it is preferable to determine in which region the engine state is based on the engine rotation speed and the fuel amount and to operate the EGR means appropriately for each region. The control flow in FIGS. 11 to 14 increases the number of functions F (N *) and increases the number of paths that branch depending on the magnitude relationship between the functions F (N *) and Q *, thereby enabling various EGR means to operate. It becomes. As a result, transition control between the LPEGR region and the HPEGR region can be performed so that changes in various states due to switching of the EGR method are smoother.

It is a lineblock diagram of an engine system showing one embodiment of the present invention. It is an engine state plane (region map) with the engine rotation speed as the horizontal axis and the fuel amount as the vertical axis. It is a region map with the normalized rotational speed as the horizontal axis and the normalized fuel amount as the vertical axis. It is an engine state plane (region map) in which a lower limit boundary is defined when an EGR boundary is approximated by a circular arc. It is a figure explaining operation | movement of the engine system of this invention, (a) is the area | region map which defined the lower limit boundary line, upper limit boundary line, LPEGR area | region, HPPEGR area | region, and transition area | region at the time of carrying out the linear approximation of the EGR boundary line, b) is an area map that defines a lower limit boundary line, an upper limit boundary line, an LPEGR area, an HPEGR area, and a transition area when the EGR boundary line is approximated by an arc. It is a figure explaining operation | movement of the engine system of this invention, (a) is the area | region map which showed when the engine load increases from a light load at the time of carrying out circular approximation of the EGR boundary line, (b) is a straight line about an EGR boundary line It is the area | region map which showed when the engine load at the time of approximation increases from light load. It is a figure explaining operation | movement of the engine system of this invention, (a) is the area | region map which showed when the engine load becomes light from high load at the time of circular approximation of the EGR boundary line, (b) is an EGR boundary line It is an area map showing when the engine load is reduced from a high load when linear approximation is performed. It is a figure explaining operation | movement of the engine system of this invention, (a) is the area | region map which showed when the engine load at the time of carrying out circular arc approximation of the EGR boundary line is estimated not to reach an EGR boundary line by high load, (B) is an area map showing when the engine load when the EGR boundary line is linearly approximated is predicted to reach the EGR boundary line at a high load. It is a figure explaining operation | movement of the engine system of this invention, and is an area | region map which showed when an engine load reduces from a high load (HPEGR area | region) to a light load (LPEGR area | region). It is a figure explaining operation | movement of the engine system of this invention, and is an area | region map which showed when an engine load increases from a light load (LPEGR area | region) to a high load (HPEGR area | region). It is a flowchart which shows the flow of control used as the basis of the engine system of this invention. It is a flowchart which shows the flow of control used as the basis of the engine system of this invention. It is a flowchart which shows the flow of control used as the basis of the engine system of this invention. It is a flowchart which shows the flow of control used as the basis of the engine system of this invention. It is a block diagram of the conventional engine system. It is a block diagram of the conventional engine system. It is a gas temperature characteristic figure in an intake manifold with respect to fuel quantity. It is a figure which shows the PCI limit in an engine state plane.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine system 2 Engine 3 Exhaust manifold 4 High-pressure stage turbocharger turbine 5 High-pressure stage turbocharger 6 High-pressure exhaust adjustment valve 7 Low-pressure stage turbocharger 8 Low-pressure stage turbocharger turbine 9 Exhaust gas switching valve 10 Exhaust gas discharge piping 11 DPF
DESCRIPTION OF SYMBOLS 12 NOx catalyst type nitrogen oxide removal apparatus 13 Intake manifold 14 High pressure EGR piping 15 High pressure EGR cooler 16 High pressure EGR valve 17 Low pressure EGR piping 18 Low pressure EGR cooler 19 Low pressure EGR valve 20 Low pressure stage turbocharger compressor 21 Intake pipe 22 Intake throttle 23 High-pressure turbocharger compressor 24 Low-pressure turbo output gas piping 25 Intake switching valve 26 High-pressure gas piping 27 Computer

Claims (8)

Whether the high-pressure EGR means for returning the exhaust gas from the exhaust manifold of the engine to the intake manifold, the low-pressure EGR means for returning the exhaust gas from the exhaust gas discharge pipe to the intake pipe, and only the low-pressure EGR means depending on the engine load A computer for controlling whether to operate only the high pressure EGR means or to operate both the low pressure EGR means and the high pressure EGR means, and to control the low pressure EGR means and the high pressure EGR means,
The computer includes an LPEGR region in which only the low-pressure EGR means is allowed to operate, an HPEGR region in which only the high-pressure EGR means is allowed to operate, and an engine state plane having the engine rotation speed and the fuel amount as two orthogonal axes. A transition region in which one or both of the low pressure EGR means and the high pressure EGR means can be operated is defined,
An engine system according to claim 1, wherein the computer determines the EGR means to be operated by referring to the engine state plane based on the current engine speed and fuel amount. A turbocharger that can switch between small-capacity drive and large-capacity drive
The computer switches the turbocharger to small capacity driving when operating only the low pressure EGR means, and switches the turbocharger to large capacity driving when operating only the high pressure EGR means. 1. The engine system according to 1. The engine is an engine capable of early fuel injection by the PCI combustion method,
In the engine state plane of the computer, a PCI region for performing fuel early injection and a non-PCI region for not performing fuel early injection are defined,
The engine system according to claim 1, wherein the PCI area is included in the LPEGR area. In the engine state plane of the computer, an EGR boundary line is defined that defines a low pressure EGR recommended region where the operation of the low pressure EGR means is desirable and a high pressure EGR recommended region where the operation of the high pressure EGR means is desirable,
A region separated by a predetermined distance or more from the EGR boundary line to the low pressure EGR recommended region side is defined as the LPEGR region, and a region separated from the EGR boundary line to the high pressure EGR recommended region side by a predetermined distance or more is defined as the HPEGR region. The engine system according to any one of claims 1 to 3, wherein a region less than a predetermined distance from the EGR boundary is defined as the transition region. The computer predicts a future engine rotation speed and fuel amount in the engine state plane from the current engine rotation speed, fuel amount and past engine rotation speed and fuel amount,
When the past engine speed and fuel amount are in the LPEGR region or the HPPEGR region, and the current engine speed and fuel amount have moved to the transition region,
If the predicted engine rotation speed and fuel amount do not move to the other EGR recommended area side beyond the EGR boundary line, the EGR means to be operated is maintained as it is in the past,
The operation of both the low pressure EGR means and the high pressure EGR means is started when the predicted engine speed and fuel amount exceed the EGR boundary and move to another EGR recommended region. 4. The engine system according to 4.   The computer includes the normalized rotational speed obtained by dividing the engine rotational speed by the maximum rotational speed of the EGR boundary line and the normalized fuel amount obtained by dividing the fuel amount by the fuel amount at the engine rotational speed of the EGR boundary line = 0. 6. The engine system according to claim 4, wherein an engine state plane is defined, and the EGR boundary is defined by a function of a fourth order or less such as a circle or a straight line.   In the computer, a lower limit boundary that is a boundary between the LPEGR region and the transition region is defined by a line whose normalized rotational speed and normalized fuel amount are smaller than the EGR boundary line by a predetermined ratio. The engine system according to claim 6, wherein an upper limit boundary line that is a boundary with the HPEGR region is defined by a line having a normalized rotational speed and a normalized fuel amount larger than the EGR boundary line by a predetermined ratio. In the computer, for each location on the engine state plane in which the engine rotation speed and the fuel amount are orthogonal two axes, a mixed gas amount obtained by adding the EGR amount to the air amount when EGR is not performed is defined. A function of MAF control for determining the EGR amount by referring to the engine state plane based on the engine rotational speed and the fuel amount of
The computer applies the MAF control to the low pressure EGR means in the LPEGR region, applies the MAF control to the high pressure EGR means in the HPEGR region, and applies the MAF control to one EGR means in the transition region. 8. The engine system according to claim 1, wherein the other EGR means is controlled so that the opening degree is gradually reduced.

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