JP2008138598A - Egr system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of performing exhaust gas recirculation while poor combustion and worsened exhaust emission are restrained at a low open air temperature and a low water temperature, in an internal combustion engine having an EGR system for performing EGR by using commonly a low pressure EGR device and a high pressure EGR device or switching them. <P>SOLUTION: The EGR system has the high pressure EGR device which returns a part of an exhaust gas flowing through an exhaust gas passage at the upstream side of a turbine of a turbocharger into the internal combustion engine by making it flow into an intake passage at the downstream side of a compressor, and a low pressure EGR device which returns a part of the exhaust gas flowing through the exhaust gas passage at the downstream side of the turbine into the internal combustion engine by making it flow into the intake passage at the upstream side of the compressor. When the temperature of a coolant for the internal combustion engine is lower than a standard temperature of the coolant, a ratio of the exhaust gas which occupies in the whole exhaust gas returned to the internal combustion engine and returned to the internal combustion engine by the high pressure EGR device is raised compared with the case of the temperature of the coolant with a normal temperature of the coolant higher than the standard temperature of the coolant. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an EGR system for an internal combustion engine.

  As a technique for reducing the amount of nitrogen oxides (NOx) generated in the combustion process of fuel in an internal combustion engine, EGR in which a part of exhaust gas flows into the internal combustion engine is known.

  With regard to this EGR technology, a high-pressure EGR device that allows a part of exhaust gas to flow into an internal combustion engine via a high-pressure EGR passage that connects an exhaust passage upstream of a turbine of a turbocharger and an intake passage downstream of a compressor, A low pressure EGR device that causes a part of the exhaust gas to flow into the internal combustion engine via a low pressure EGR passage that connects the downstream exhaust passage and the intake passage upstream of the compressor, and the high pressure EGR device according to the operating state of the internal combustion engine In addition, a technique has been proposed in which EGR can be carried out in a wider range of operating states of an internal combustion engine by performing EGR by using or switching between and a low pressure EGR device.

For example, EGR is performed using a high pressure EGR device when the exhaust temperature is low such as during low load operation, and EGR is performed using a low pressure EGR device when the exhaust temperature is high such as during high load operation. A technique for suppressing the intake air temperature from becoming excessively high has been proposed (see Patent Document 1).
Japanese Patent Application Laid-Open No. 07-233761 Japanese Patent Laid-Open No. 2004-162675 JP 2004-197634 A

  By the way, since the path length of the high pressure EGR passage is relatively short, the temperature of the exhaust gas (hereinafter referred to as high pressure EGR gas) flowing into the internal combustion engine via the high pressure EGR device tends to be relatively high. On the other hand, for the exhaust gas flowing into the internal combustion engine via the low pressure EGR device (hereinafter referred to as low pressure EGR gas), the path length of the low pressure EGR passage is long, and the EGR cooler provided in the low pressure EGR passage or the intercooler provided in the intake passage. Since the low pressure EGR gas is cooled at, the temperature of the low pressure EGR gas tends to be relatively low.

  The flow of low-temperature low-pressure EGR gas into the internal combustion engine is advantageous in terms of NOx reduction effect and fuel efficiency. However, when the ambient environment temperature of the internal combustion engine is low (for example, in winter when the temperature is low) or when the temperature of the internal combustion engine itself is If the low-temperature low-pressure EGR gas is allowed to flow into the internal combustion engine in a situation where the intake air temperature is likely to decrease, such as when it is low (for example, immediately after start-up), the intake air temperature may decrease excessively, leading to poor combustion such as misfire.

  The present invention has been made in view of such problems, and particularly in an internal combustion engine having an EGR system that performs EGR by using both a low pressure EGR device and a high pressure EGR device, particularly at low outside air temperature and low water temperature. An object of the present invention is to provide a technique for suppressing instability of combustion and deterioration of exhaust emission.

To achieve the above object, an EGR system for an internal combustion engine according to the present invention includes a turbocharger having a compressor in an intake passage of the internal combustion engine and a turbine in an exhaust passage, an exhaust passage upstream of the turbine, and downstream of the compressor. High pressure EGR means for allowing a part of exhaust gas to flow into the internal combustion engine through a high pressure EGR passage connecting the intake passage of the engine, and a low pressure EGR passage connecting the exhaust passage downstream of the turbine and the intake passage upstream of the compressor Low pressure EGR means for causing a part of the exhaust gas to flow into the internal combustion engine via the internal combustion engine, EGR control means for performing EGR by using or switching the high pressure EGR means and the low pressure EGR means according to the operating state of the internal combustion engine, Determining means for determining whether or not there is a possibility of occurrence of combustion failure in the EGR control means, the EGR control means When it is determined by the determination means that there is a possibility of poor combustion when the operating state of the internal combustion engine belongs to at least a predetermined operation region where EGR is performed using the low-pressure EGR means, Compared to a case where it is not determined that there is a possibility of a failure, the ratio of high-pressure EGR gas to all exhaust gas (hereinafter referred to as all EGR gas) flowing into the internal combustion engine is increased.

  Here, the “predetermined operating region where EGR is performed using at least the low pressure EGR means” means the range of operating states where the EGR is performed using only the low pressure EGR means by the EGR control means (hereinafter referred to as LPL region) and the low pressure. This is an operation region including an operation state range (hereinafter, MIX region) in which EGR is performed by using both the EGR unit and the high pressure EGR unit, and is determined in advance.

  Further, as a case where the determination means determines that “combustion failure may occur in the internal combustion engine”, for example, when the temperature of the ambient environment of the internal combustion engine is low (for example, in winter when the outside air temperature decreases), A case where the temperature of the intake air is likely to decrease can be exemplified as in the case where the temperature of the engine itself is low (for example, immediately after the engine is not sufficiently warmed up).

  According to the above configuration, when the operation state of the internal combustion engine belongs to the LPL region and the determination unit determines that there is a possibility that combustion failure may occur, the ratio of the high-pressure EGR gas in the total EGR gas is The EGR is performed by changing the value from 0% to a value larger than 0%. In other words, part or all of the range of the operating state defined as the LPL region at room temperature when it is not determined that there is a possibility of occurrence of combustion failure by the determining means is temporarily redefined as the MIX region and EGR. Is done.

  The change in the ratio of the high pressure EGR gas in this case may include a case where the ratio of the high pressure EGR gas is increased from 0% to 100%. In other words, a part or all of the range of the operating state defined as the LPL region at room temperature when it is not determined that there is a possibility of occurrence of a combustion failure by the determination means is temporarily redefined as the HPL region and EGR. May be included. Here, the “HPL region” means a range of operating states in which EGR is performed using only the high pressure EGR means.

  Further, when the operation state of the internal combustion engine belongs to the MIX region, if the determination unit determines that there is a possibility that combustion failure may occur, the ratio of the high-pressure EGR gas in the total EGR gas is determined by the determination unit. EGR is performed by changing to a ratio higher than the ratio of high-pressure EGR gas at normal temperature at which it is not determined that there is a possibility of occurrence of poor combustion.

  The change in the ratio of the high pressure EGR gas in this case may include a case where the ratio of the high pressure EGR gas is increased from a certain ratio at normal temperature to 100%. In other words, part or all of the range of the operating state defined as the MIX region at room temperature when it is not determined that there is a possibility of occurrence of a combustion failure by the determination means is temporarily redefined as the HPL region and EGR. May be included.

As described above, according to the present invention, in a situation where the intake air temperature tends to decrease such as at low outside air temperature or low water temperature, the high-temperature high-pressure EGR gas flows into the internal combustion engine more than at normal temperature. In addition, an excessive decrease in the intake air temperature is suppressed. As a result, even when the outside air temperature or the water temperature is low, it is possible to suitably suppress the occurrence of a combustion failure such as misfire or the discharge of a large amount of unburned fuel components.

  In the present invention, even if it is determined by the determination means that there is a possibility that a combustion failure may occur, the operation state of the internal combustion engine is a predetermined value in which EGR is performed using at least the low-pressure EGR means described above. When belonging to a predetermined high load region in the operation region, the EGR may be performed without changing the ratio of the high pressure EGR gas in all the EGR gases while maintaining the ratio of the high pressure EGR gas at normal temperature.

  Here, the “predetermined high load region” refers to a range of operating states in which fuel consumption may increase or exhaust emission may deteriorate if EGR is performed with a high pressure EGR gas ratio being increased. Predetermined.

  In the present invention, the outside air temperature can be adopted as a parameter representing the ambient environment temperature of the internal combustion engine. Further, the cooling water temperature of the internal combustion engine can be adopted as a parameter representative of the temperature of the internal combustion engine itself. That is, the determination means can determine whether or not there is a possibility of poor combustion based on the outside air temperature or the cooling water temperature.

  For example, when the outside air temperature is lower than a predetermined reference outside air temperature, or when the cooling water temperature is lower than a predetermined reference cooling water temperature, it can be determined that there is a possibility that combustion failure may occur. Here, the predetermined reference outside air temperature is a lower limit value of the outside air temperature at which there is no possibility that the intake air temperature is excessively lowered even when the EGR control at normal temperature is performed. The predetermined reference cooling water temperature is a lower limit value of the cooling water temperature at which there is no possibility that the intake air temperature is excessively lowered even when the EGR control at normal temperature is performed.

  In order to solve the above-described problems, the present invention provides a turbocharger having a compressor in an intake passage of an internal combustion engine and having a turbine in an exhaust passage, an exhaust passage upstream from the turbine, and an intake passage downstream from the compressor. A high pressure EGR means for allowing a part of the exhaust gas to flow into the internal combustion engine via a high pressure EGR passage connecting the engine, and a low pressure EGR passage connecting an exhaust passage downstream of the turbine and an intake passage upstream of the compressor. Low-pressure EGR means for causing a part of exhaust gas to flow into the internal combustion engine, EGR control means for performing EGR by using or switching the high-pressure EGR means and the low-pressure EGR means in accordance with the operating state of the internal combustion engine, and an internal combustion engine Water temperature measuring means for measuring the cooling water temperature, and the EGR control means occupies the exhaust gas flowing into the internal combustion engine. The ratio of the exhaust gas to flow into the internal combustion engine by pressure EGR means may be an internal combustion engine EGR system, characterized by variably controlled in accordance with the coolant temperature measured by the temperature measuring means.

  As described above, the temperature of the high pressure EGR gas is relatively high and the temperature of the low pressure EGR gas is relatively low. Therefore, the higher the ratio of low-pressure EGR gas in all EGR gases (the lower the ratio of high-pressure EGR gas), the lower the intake air temperature when EGR is performed. Conversely, the lower the ratio of low-pressure EGR gas in all EGR gases (the higher the ratio of high-pressure EGR gas), the higher the intake air temperature when EGR is performed.

  According to the above configuration, since the ratio of the low-pressure EGR gas in the total EGR gas is variably controlled according to the cooling water temperature of the internal combustion engine, the intake air temperature when EGR is performed is optimized regardless of the temperature of the internal combustion engine. In addition, fuel consumption characteristics and exhaust emission can be improved.

  For example, when the cooling water temperature is low, the temperature of the internal combustion engine is low, and if low-temperature low-pressure EGR gas is allowed to flow into the internal combustion engine, the intake air temperature may excessively decrease. Therefore, by reducing the ratio of low-pressure EGR gas in all EGR gas and making most or all of the total EGR gas high-pressure EGR gas, it is possible to suppress a decrease in intake air temperature when performing EGR, It is possible to suppress problems such as misfiring and other combustion failures or a large amount of unburned hydrocarbons being discharged.

  On the other hand, when the cooling water temperature is high, there is no possibility that the intake air temperature will decrease excessively even if low-pressure EGR gas is introduced into the internal combustion engine. Therefore, the ratio of low-pressure EGR gas in all EGR gases is increased, and high-pressure EGR means and It is preferred to perform EGR using both low pressure EGR means. Thereby, since EGR is performed using the low pressure EGR means, the turbocharging efficiency of the turbocharger is increased. Further, the pump loss is reduced as compared with the case where all the EGR gas is caused to flow into the internal combustion engine using the high pressure EGR means. Therefore, the fuel characteristics resulting from the implementation of EGR can be improved.

  As described above, the lower the coolant temperature, the lower the ratio of the low pressure EGR gas in the total EGR gas (the higher the ratio of the high pressure EGR gas). Realizes fuel efficiency and exhaust emissions. The ratio of the low-pressure EGR gas in the total EGR gas may be continuously variably controlled according to the cooling water temperature, or may be changed in stages. In the first aspect of the present invention described above, when the determination means is configured to determine whether or not there is a possibility of combustion failure in the internal combustion engine based on the coolant temperature, the present invention described above. In the second embodiment, it can be said that this corresponds to a configuration in which the ratio of the low-pressure EGR gas in the total EGR gas is changed in two stages according to the cooling water temperature.

  The temperature of the internal combustion engine can also be estimated based on the intake passage wall surface temperature, the engine oil temperature, and the like in addition to the coolant temperature.

  In addition, said each structure can be employ | adopted combining as much as possible.

  According to the present invention, in an internal combustion engine equipped with an EGR system that performs EGR using both a low pressure EGR device and a high pressure EGR device, EGR while suppressing poor combustion and deterioration of exhaust emission even at low outside air temperature and low water temperature. It becomes possible to do.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram schematically illustrating a schematic configuration of an intake system, an exhaust system, and a control system of an internal combustion engine to which an EGR system for an internal combustion engine according to the present embodiment is applied. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.

  An intake manifold 17 is connected to the cylinder 2 of the internal combustion engine 1 via an intake port (not shown). An intake pipe 3 is connected to the intake manifold 17. A second throttle 9 capable of adjusting the amount of intake air flowing through the intake pipe 3 is disposed in the intake pipe 3 upstream of the intake manifold 17. The intake pipe 3 upstream of the second throttle 9 is provided with an intercooler 8 for cooling the intake air. A compressor 11 of a turbocharger 13 that operates using exhaust energy as a drive source is disposed in the intake pipe 3 upstream of the intercooler 8. A first throttle 6 capable of adjusting the amount of fresh air flowing into the intake pipe 3 is disposed in the intake pipe 3 upstream of the compressor 11.

An exhaust manifold 18 is connected to the cylinder 2 of the internal combustion engine 1 via an exhaust port (not shown). The exhaust pipe 4 is connected to the exhaust manifold 18. A turbine 12 of a turbocharger 13 is disposed in the exhaust pipe 4. The turbocharger 13 is a variable capacity turbocharger including a nozzle vane 5 that can change the exhaust flow rate characteristic of the turbine 12. An exhaust purification device 10 is provided in the exhaust pipe 4 downstream of the turbine 12. The exhaust purification device 10 is a particulate filter (hereinafter referred to as a filter) that collects particulate matter in the exhaust, and is supported on the filter. When the exhaust is in an oxidizing atmosphere, the exhaust purifier 10 stores NOx in the exhaust, and the exhaust is reduced. And an NOx storage reduction catalyst that purifies NOx in the exhaust gas by releasing / reducing NOx stored in the atmosphere. An exhaust throttle valve 19 capable of adjusting the amount of exhaust flowing through the exhaust pipe 4 is disposed in the exhaust pipe 4 downstream of the exhaust purification device 10. Note that the exhaust throttle valve 19 may be disposed in the exhaust pipe 4 downstream of the connecting portion of the low pressure EGR passage 31 described later.

  The internal combustion engine 1 is provided with a high-pressure EGR device 40 that guides a part of the exhaust gas flowing through the exhaust pipe 4 to the intake pipe 3 at a high pressure and flows into the cylinder 2. The high pressure EGR device 40 includes a high pressure EGR passage 41 and a high pressure EGR valve 42. The high pressure EGR passage 41 connects the exhaust pipe 4 upstream of the turbine 12 and the intake pipe 3 downstream of the second throttle 9. A part of the exhaust gas is guided to the intake pipe 3 through the high-pressure EGR passage 41. In this embodiment, the exhaust gas flowing into the cylinder 2 via the high pressure EGR passage 41 is referred to as high pressure EGR gas.

  The high pressure EGR valve 42 is a flow rate adjustment valve capable of adjusting the amount of exhaust gas flowing through the high pressure EGR passage 41. The high-pressure EGR gas is metered by changing the opening degree of the high-pressure EGR valve 42. The metering of the high pressure EGR gas can also be performed by changing the differential pressure between the upstream and downstream of the high pressure EGR passage 41 by changing the opening of the second throttle 9. Further, the high pressure EGR gas can be metered by changing the opening degree of the nozzle vane 5.

  The internal combustion engine 1 is provided with a low pressure EGR device 30 that guides a part of the exhaust gas flowing through the exhaust pipe 4 to the intake pipe 3 at a low pressure and flows into the cylinder 2. The low pressure EGR device 30 includes a low pressure EGR passage 31, a low pressure EGR valve 32, and a low pressure EGR cooler 33. The low pressure EGR passage 31 connects the exhaust pipe 4 downstream of the exhaust throttle valve 19 and the intake pipe 3 upstream of the compressor 11 and downstream of the first throttle 6. A part of the exhaust gas is guided to the intake pipe 3 through the low-pressure EGR passage 31. In this embodiment, the exhaust gas flowing into the cylinder 2 via the low pressure EGR passage 31 is referred to as low pressure EGR gas.

  The low pressure EGR valve 32 is a flow rate adjustment valve capable of adjusting the amount of exhaust gas flowing through the low pressure EGR passage 31. Metering of the low pressure EGR gas is performed by changing the opening of the low pressure EGR valve 32. The low-pressure EGR gas can be regulated by changing the opening of the first throttle 6 to change the differential pressure between the upstream and downstream of the low-pressure EGR passage 31. The low pressure EGR cooler 33 cools the low pressure EGR gas passing through the low pressure EGR passage 31.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 20 that controls the engine. The ECU 20 connects a read-only memory (ROM), a random access memory (RAM), a central processing unit (CPU), an input / output port, a digital analog converter (DA converter), an analog digital converter (AD converter), etc. with a bidirectional bus. The microcomputer has a known configuration as described above.

  The ECU 20 performs various basic controls known in the diesel engine such as fuel injection control in accordance with the operation state of the internal combustion engine 1 or a request from the driver. For this purpose, the internal combustion engine 1 in this embodiment includes an air flow meter 7 that detects the flow rate of fresh air flowing into the intake pipe 3, a water temperature sensor 14 that measures the cooling water temperature of the internal combustion engine 1, and an accelerator pedal (not shown). An accelerator opening sensor 15 for detecting a stepping amount (accelerator opening) of the (omitted), a crank position sensor 16 for detecting a rotation phase (crank angle) of a crankshaft (not shown) of the internal combustion engine 1, and a diesel engine are generally used. Provided sensors (not shown) are provided.

  These sensors are connected to the ECU 20 via electric wiring, and output signals from the sensors are input to the ECU 20. The ECU 20 is connected to devices such as a drive device for driving the first throttle 6, the second throttle 9, the exhaust throttle valve 19, the low pressure EGR valve 32, and the high pressure EGR valve 42 through electric wiring. These devices are controlled in accordance with a control signal output from.

  ECU20 grasps | ascertains the driving | running state of the internal combustion engine 1, and a driver | operator's request | requirement based on the detection value by each sensor. For example, the ECU 20 determines the operating state of the internal combustion engine 1 based on the engine speed calculated from the crank angle input from the crank position sensor 16 and the engine load calculated from the accelerator opening input from the accelerator opening sensor 15. To detect. Then, the low pressure EGR valve 32, the high pressure EGR valve 42, and the like are controlled based on the detected engine operating state and the driver's request to control the EGR gas amount and the intake air amount.

  Next, EGR control performed by the ECU 20 will be described.

  FIG. 2 is a conceptual diagram of an EGR control map representing combinations of the high-pressure EGR device 40 and the low-pressure EGR device 30 that are used for EGR execution and are determined for each operating state region of the internal combustion engine 1. 2 represents the engine speed of the internal combustion engine 1, and the vertical axis represents the engine load of the internal combustion engine 1.

  As shown in FIG. 2, in the EGR system of the present embodiment, when the operating state of the internal combustion engine 1 is a low load, EGR is performed using only the high-pressure EGR device 40. The range of operating states in which EGR is performed using only the high-pressure EGR device 40 is hereinafter referred to as “HPL region”. When the operating state of the internal combustion engine 1 is a medium load, EGR is performed using both the high pressure EGR device 40 and the low pressure EGR device 30. The range of operating states in which EGR is performed using the high pressure EGR device 40 and the low pressure EGR device 30 together is hereinafter referred to as a “MIX region”. Further, when the operating state of the internal combustion engine 1 is a high load, EGR is performed using only the low pressure EGR device 30. The range of the operating state in which EGR is performed using only the low pressure EGR device 30 is hereinafter referred to as “LPL region”.

  In the EGR control map shown in FIG. 2, the operation state of the internal combustion engine is illustrated as being divided into three regions of the HPL region, the MIX region, and the LPL region. However, the method of dividing the operation state of the internal combustion engine is as follows. It is not limited to this. For example, as shown in FIG. 3, an EGR control map in which the low load region is defined as the HPL region and the other high load side region is defined as the LPL region is also conceivable. Alternatively, as shown in FIG. 4, an EGR control map may be considered in which the low load region is defined as a MIX region and the other high load side region is defined as an LPL region.

  Specific operating state ranges defining the LPL region, the MIX region, and the HPL region, the high pressure EGR gas amount in each region, the low pressure EGR gas amount, and the total exhaust gas flowing into the internal combustion engine by the EGR system (hereinafter referred to as the total EGR gas). The target values of various parameters related to EGR control, such as the ratio of the exhaust high-pressure EGR gas and low-pressure EGR gas to the exhaust gas), the intake EGR rate matches the predetermined target EGR rate in each operating state, and combustion in the internal combustion engine The characteristics, exhaust emissions, fuel consumption characteristics associated with the implementation of EGR, and the like are determined in advance by experiments or the like so as to satisfy desired performance requirements. The target value of the high pressure EGR gas amount thus determined is hereinafter referred to as “basic high pressure EGR gas amount”, and the target value of the low pressure EGR gas amount is referred to as “basic low pressure EGR gas amount”, the basic high pressure EGR gas amount and the basic low pressure EGR gas. The ratio of the high pressure EGR gas in the total EGR gas determined by the amount is hereinafter referred to as “basic high pressure EGR ratio”, and the ratio of the low pressure EGR gas in the total EGR gas is hereinafter referred to as “basic low pressure EGR ratio”. The EGR control map defined by the basic high pressure EGR gas amount and the basic low pressure EGR gas amount determined for each operation state is hereinafter referred to as a “basic EGR control map”.

  The basic low pressure EGR valve opening is determined as the opening of the low pressure EGR valve 32 so that the low pressure EGR gas amount is the basic low pressure EGR gas amount during steady operation of the internal combustion engine 1, and the high pressure EGR gas amount is determined as the basic high pressure EGR amount. The basic high pressure EGR valve opening degree is obtained as the opening degree of the high pressure EGR valve 42 to be the gas amount, and is stored in the ROM of the ECU 20 respectively.

  The ECU 20 reads the basic low pressure EGR valve opening and the basic high pressure EGR valve opening from the ROM in accordance with the operating state of the internal combustion engine 1, and the low pressure EGR so that the opening of the low pressure EGR valve 32 becomes the basic low pressure EGR valve opening. While controlling the valve 32, the high pressure EGR valve 42 is controlled so that the opening degree of the high pressure EGR valve 42 becomes the basic high pressure EGR valve opening degree.

  By the way, the high-pressure EGR passage 41 has a relatively short path length, and the high-pressure EGR gas is difficult to be cooled in the flow process. Therefore, by performing EGR using the high-pressure EGR device 40, relatively high-temperature exhaust gas is sent to the internal combustion engine 1. Inflow. On the other hand, the path length of the low pressure EGR passage 31 is relatively long, and the low pressure EGR cooler 33, the intercooler 8 and the like are disposed on the flow path of the low pressure EGR gas, so that the low pressure EGR gas is cooled in the flow process. The Therefore, by performing EGR using the low pressure EGR device 30, relatively low temperature exhaust gas flows into the internal combustion engine 1.

  When EGR is performed using the low-pressure EGR device 30, low-temperature low-pressure EGR gas is supercharged to the internal combustion engine 1 by the turbocharger 13, which is advantageous in terms of NOx reduction effect and fuel consumption performance. When the ambient temperature is low (for example, in the winter when the outside air temperature is low) or when the temperature of the internal combustion engine itself is low (for example, immediately after the engine is started), low-temperature low-pressure EGR gas enters the internal combustion engine 1 in situations where the intake air temperature tends to decrease. When it flows in, there is a possibility that the intake air temperature is excessively lowered to cause a combustion failure such as misfire.

  Therefore, in this embodiment, when there is a possibility that the intake air temperature is excessively lowered and combustion failure may occur, an operation state region where EGR is performed using the low pressure EGR device 30, that is, a MIX region or an LPL region. The EGR control map is corrected so that EGR is performed so that the ratio of the high-pressure EGR gas in all the EGR gases is increased in a part or all of the region.

  As a result, even if the intake air temperature is likely to decrease, the high-temperature high-pressure EGR gas flows into the internal combustion engine 1 more than the basic high-pressure EGR gas amount at normal temperature. It is possible to suitably suppress the occurrence of poor combustion such as misfire due to excessive decrease in the amount of fuel.

  In the present embodiment, based on the cooling water temperature and / or the outside air temperature measured by the water temperature sensor 14, whether or not “the situation where there is a possibility that the intake air temperature is excessively lowered and combustion failure occurs” is determined. Determine. Specifically, when the cooling water temperature Tw is lower than a predetermined reference cooling water temperature Twth and / or when the outside air temperature Ta is lower than the predetermined reference outside air temperature Tath, a combustion failure may occur. It is determined that Hereinafter, the situation in which it is determined that there is a possibility that a combustion failure may occur is referred to as “at the time of low water temperature”. Conversely, when the cooling water temperature is equal to or higher than the reference cooling water temperature and the outside air temperature is equal to or higher than the reference outside air temperature, it is not determined that there is a possibility that a combustion failure may occur. A situation in which it is not determined that there is a possibility that a combustion failure may occur is referred to as “at room temperature”.

  Hereinafter, some specific examples of correction of the EGR control map will be described.

FIG. 5 is a diagram showing a correction example for the basic EGR control map in which the operating state of the internal combustion engine is divided into the HPL region, the MIX region, and the LPL region as shown in FIG. In this example, the ratio of the high-pressure EGR gas is increased from 0% to a predetermined ratio greater than 0% at a low water temperature in a part of the low load side (that is, the MIX region side) in the LPL region. Further, the high pressure EGR ratio in the MIX region is increased compared with the basic high pressure EGR ratio at the time of low water temperature, and the high pressure EGR ratio is smaller than 100% particularly in a part of the low load side (that is, the HPL region side). Increase from a predetermined ratio to 100%.

  That is, the operating state belonging to the shaded portion A, which was defined as the operating state belonging to the LPL region at normal temperature, is redefined as the operating state belonging to the MIX region, and the LPL region is reduced. Further, the operating state belonging to the hatched portion B, which was defined as the operating state belonging to the MIX region at normal temperature, is redefined as the operating state belonging to the HPL region, and the HPL region is expanded.

  By correcting the basic EGR control map in this way, the high-pressure EGR device 40 and the low-pressure EGR device 30 can be operated at the low water temperature even in the operation state belonging to the shaded portion A where the EGR is performed using only the low-pressure EGR device 30 at the normal temperature. Since the EGR is performed in combination, the high-temperature high-pressure EGR gas flows into the internal combustion engine 1, and it is possible to suppress the intake air temperature from excessively decreasing. Further, even in the operating state belonging to the MIX region, more high-pressure EGR gas flows into the internal combustion engine 1 than at normal temperature, so that an excessive decrease in the intake air temperature can be similarly suppressed.

  FIG. 6 is a diagram showing a correction example for the basic EGR control map in which the operating state of the internal combustion engine is divided into the HPL region and the LPL region as shown in FIG. 3. In this example, the ratio of the high-pressure EGR gas is increased from 0% to 100% at a low water temperature in a part of the LPL region on the low load side (that is, the HPL region side). That is, the operating state belonging to the shaded portion C, which was defined as the operating state belonging to the LPL region at normal temperature, is redefined as the operating state belonging to the HPL region, and the LPL region is reduced.

  By correcting the basic EGR control map in this way, even in an operating state belonging to the shaded portion C where EGR is performed using only the low pressure EGR device 30 at normal temperature, EGR is performed using only the high pressure EGR device 40 at low water temperature. Therefore, the high-temperature high-pressure EGR gas flows into the internal combustion engine 1, and the intake air temperature can be prevented from excessively decreasing.

  FIG. 7 is a diagram showing different correction examples for the basic EGR control map shown in FIG. In this example, the ratio of the high pressure EGR gas is increased from 0% to a predetermined ratio larger than 0% at a low water temperature in a part of the low load side (that is, the HPL region side) in the LPL region. That is, the operating state belonging to the hatched portion D, which was defined as the operating state belonging to the LPL region at normal temperature, is redefined as the operating state belonging to the MIX region, and the LPL region is reduced.

  By correcting the basic EGR control map in this way, the high-pressure EGR device 40 and the low-pressure EGR device 30 can be operated at the low water temperature even in the operation state belonging to the shaded portion D where the EGR is performed using only the low-pressure EGR device 30 at the normal temperature. Since the EGR is performed in combination, the high-temperature high-pressure EGR gas flows into the internal combustion engine 1, and it is possible to suppress the intake air temperature from excessively decreasing.

  FIG. 8 is a diagram showing a correction example for the basic EGR control map in which the operating state of the internal combustion engine is divided into the MIX region and the LPL region as shown in FIG. In this example, the ratio of the high-pressure EGR gas is increased from 0% to a predetermined ratio greater than 0% at a low water temperature in a part of the low load side (that is, the MIX region side) in the LPL region. That is, the operating state belonging to the shaded portion E, which was defined as the operating state belonging to the LPL region at normal temperature, is redefined as the operating state belonging to the MIX region, and the LPL region is reduced.

  By correcting the basic EGR control map in this manner, the high-pressure EGR device 40 and the low-pressure EGR device 30 can be operated at the low water temperature even in the operating state belonging to the shaded portion E where the EGR is performed using only the low-pressure EGR device 30 at the normal temperature. Since the EGR is performed in combination, the high-temperature high-pressure EGR gas flows into the internal combustion engine 1, and it is possible to suppress the intake air temperature from excessively decreasing.

  FIG. 9 is a diagram showing different correction examples for the basic EGR control map shown in FIG. In this example, the high pressure EGR ratio in the MIX region is increased compared to the basic high pressure EGR ratio at the time of low water temperature. By correcting the basic EGR control map in this manner, in the operating state belonging to the MIX region, a larger amount of high-pressure EGR gas flows into the internal combustion engine 1 than at normal temperature, so the intake air temperature decreases excessively. Can be suppressed.

  FIG. 10 is a diagram showing an example of increasing the high-pressure EGR ratio from a predetermined ratio smaller than 100% to 100% in the correction example shown in FIG. 9, particularly in a partial region on the low load side in the MIX region. is there. In this example, the operating state belonging to the shaded portion F, which was defined as the operating state belonging to the MIX region at normal temperature, is redefined as the operating state belonging to the HPL region, and the HPL region is expanded.

  By correcting the basic EGR control map in this way, only the high pressure EGR device 40 is operated at the low water temperature in the operation state belonging to the shaded portion F where the high pressure EGR device 40 and the low pressure EGR device 30 are used in combination at the normal temperature. Since the EGR is performed using the high-temperature EGR gas, the high-temperature high-pressure EGR gas flows into the internal combustion engine 1, and the intake air temperature can be prevented from excessively decreasing.

  Hereinafter, a specific execution procedure of the EGR control map correction control of this embodiment performed at the time of low water temperature will be described with reference to FIG. FIG. 11 is a flowchart showing an EGR control map correction control routine. This routine is repeatedly executed every predetermined time while the internal combustion engine 1 is operating.

  In step S101, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the engine load is calculated based on the accelerator opening measured by the accelerator opening sensor 15 and the engine speed is calculated based on the crank angle measured by the crank position sensor 16.

  In step S102, the ECU 20 acquires the coolant temperature Tw of the internal combustion engine 1. Specifically, the cooling water temperature is directly measured by the water temperature sensor 14.

  In step S103, the ECU 20 determines whether there is a possibility that a combustion failure may occur in the internal combustion engine 1, that is, whether the intake air temperature is likely to decrease. Specifically, it is determined whether or not the cooling water temperature Tw acquired in step S102 is lower than the reference cooling water temperature Twth. If an affirmative determination is made in step S103, the ECU 20 proceeds to step S104. On the other hand, if a negative determination is made in step S103, the ECU 20 proceeds to step S106.

  In step S104, the ECU 20 corrects the basic EGR control map as described above.

  In step S105, the ECU 20 performs EGR according to the EGR control map corrected in step S104.

  In step S106, the ECU 20 performs EGR according to the basic EGR control map.

  After executing step S105 or step S106, the ECU 20 once ends the execution of this routine.

  The embodiment described above is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the gist of the present invention. For example, in the above embodiment, EGR is performed by switching two different EGR control maps, that is, a correction EGR control map used at low water temperature and a basic EGR control map used at normal temperature, according to the cooling water temperature. The ratio may be variably controlled to a continuous value or a plurality of step values as a function of the cooling water temperature. In this case, as shown in FIG. 12, it is preferable to variably control the low pressure EGR ratio so that the lower the cooling water temperature is, the smaller the low pressure EGR ratio is. By doing this, when the cooling water temperature is low, EGR is mainly performed using the high pressure EGR device 40, so that a large amount of high temperature high pressure EGR gas flows into the internal combustion engine 1, and the intake air temperature decreases excessively. It is possible to suppress combustion failure and generation of a large amount of unburned fuel components. Further, when the cooling water temperature is high, EGR is performed by using both the low pressure EGR device 30 and the high pressure EGR device 40, so that the supercharging efficiency of the turbocharger 13 is increased by using the low pressure EGR device 30, and the high pressure EGR ratio is increased. By lowering the pump loss, the pump loss can be reduced and the fuel consumption can be improved.

  Further, the temperature of the internal combustion engine can be estimated based on the intake passage wall surface temperature, the engine oil temperature, and the like in addition to the coolant temperature.

It is a figure which shows schematic structure of the intake system of the internal combustion engine to which the EGR system of Example 1 is applied, an exhaust system, and a control system. It is a figure which shows an example of the basic EGR control map which divides | segments the area | region of the operating state of an internal combustion engine into a HPL area | region, a MIX area | region, and a LPL area | region in the EGR system of Example 1. FIG. It is a figure which shows an example of the basic EGR control map which divides | segments the area | region of the driving | running state of an internal combustion engine into a HPL area | region and a LPL area | region in the EGR system of Example 1. FIG. It is a figure which shows an example of the basic EGR control map which divides | segments the area | region of the operating state of an internal combustion engine into a MIX area | region and a LPL area | region in the EGR system of Example 1. FIG. It is a figure which shows an example of the correction | amendment made at the time of low water temperature with respect to the basic EGR control map which divides | segments the area | region of the driving | running state of an internal combustion engine into a HPL area | region, a MIX area | region, and a LPL area | region in the EGR system of Example 1. FIG. It is a figure which shows an example of the correction | amendment made at the time of low water temperature with respect to the basic EGR control map which divides | segments the area | region of the operating state of an internal combustion engine into a HPL area | region and a LPL area | region in the EGR system of Example 1. FIG. It is a figure which shows an example of the correction | amendment made at the time of low water temperature with respect to the basic EGR control map which divides | segments the area | region of the operating state of an internal combustion engine into a HPL area | region and a LPL area | region in the EGR system of Example 1. FIG. It is a figure which shows an example of the correction | amendment made at the time of low water temperature with respect to the basic EGR control map which divides | segments the area | region of the driving | running state of an internal combustion engine into a MIX area | region and a LPL area | region in the EGR system of Example 1. FIG. It is a figure which shows an example of the correction | amendment made at the time of low water temperature with respect to the basic EGR control map which divides | segments the area | region of the driving | running state of an internal combustion engine into a MIX area | region and a LPL area | region in the EGR system of Example 1. FIG. It is a figure which shows an example of the correction | amendment made at the time of low water temperature with respect to the basic EGR control map which divides | segments the area | region of the driving | running state of an internal combustion engine into a MIX area | region and a LPL area | region in the EGR system of Example 1. FIG. 3 is a flowchart illustrating an EGR control map correction control routine in the EGR system of the first embodiment. It is a figure which shows the relationship between the cooling water temperature in the case of changing a low pressure EGR ratio according to a cooling water temperature in the EGR system of Example 1, and a low pressure EGR ratio.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Intake pipe 4 Exhaust pipe 5 Nozzle vane 6 1st throttle 7 Air flow meter 8 Intercooler 9 2nd throttle 10 Exhaust purification device 11 Compressor 12 Turbine 13 Turbocharger 14 Water temperature sensor 15 Accelerator opening sensor 16 Crank position sensor 17 Intake manifold 18 Exhaust manifold 19 Exhaust throttle valve 20 ECU
30 Low pressure EGR device 31 Low pressure EGR passage 32 Low pressure EGR valve 33 Low pressure EGR cooler 40 High pressure EGR device 41 High pressure EGR passage 42 High pressure EGR valve

Claims (7)

A turbocharger having a compressor in the intake passage of the internal combustion engine and a turbine in the exhaust passage;
High-pressure EGR means for allowing a part of the exhaust gas to flow into the internal combustion engine via a high-pressure EGR passage connecting an exhaust passage upstream of the turbine and an intake passage downstream of the compressor;
Low pressure EGR means for allowing a part of the exhaust gas to flow into the internal combustion engine via a low pressure EGR passage connecting an exhaust passage downstream of the turbine and an intake passage upstream of the compressor;
EGR control means for performing EGR by using or switching the high pressure EGR means and the low pressure EGR means in accordance with the operating state of the internal combustion engine;
Determination means for determining whether or not there is a possibility of occurrence of poor combustion in the internal combustion engine;
With
When the EGR control means determines that there is a possibility that a combustion failure may occur when the operating state of the internal combustion engine belongs to a predetermined operating region where EGR is performed using at least the low pressure EGR means. The ratio of the exhaust gas flowing into the internal combustion engine using the high-pressure EGR means occupying the total exhaust gas flowing into the internal combustion engine is increased compared with the normal time when it is not determined that there is a possibility that a combustion failure may occur. An EGR system for an internal combustion engine. In claim 1,
The EGR control means, when it is determined by the determination means that a combustion failure may occur in a part of the operation region where EGR is performed using only the low pressure EGR means at the normal time, An EGR system for an internal combustion engine, wherein the operation region is changed to an operation region in which EGR is performed using both the high pressure EGR means and the low pressure EGR means, or an operation region in which EGR is performed using only the high pressure EGR means. In claim 1 or 2,
When the EGR control means determines that there is a possibility that combustion failure may occur in a part of an operation region where EGR is performed by using the high pressure EGR means and the low pressure EGR means in the normal time. In the EGR system for an internal combustion engine, the operation region is changed to an operation region in which EGR is performed using only the high pressure EGR means. In any one of Claims 1-3,
The EGR control means may determine that there is a possibility that a combustion failure may occur when the operation state of the internal combustion engine belongs to a predetermined high load area within the predetermined operation area. An EGR system for an internal combustion engine, wherein the ratio of exhaust gas flowing into the internal combustion engine is not increased by using the high pressure EGR means occupying in all exhaust gas flowing into the internal combustion engine. In any one of Claims 1-4,
The EGR system for an internal combustion engine, wherein the determination means determines whether or not there is a possibility of poor combustion based on an outside air temperature and / or a cooling water temperature of the internal combustion engine. A turbocharger having a compressor in the intake passage of the internal combustion engine and a turbine in the exhaust passage;
High-pressure EGR means for allowing a part of exhaust gas to flow into the internal combustion engine via a high-pressure EGR passage connecting an exhaust passage upstream of the turbine and an intake passage downstream of the compressor;
Low pressure EGR means for allowing a part of exhaust gas to flow into the internal combustion engine via a low pressure EGR passage connecting an exhaust passage downstream of the turbine and an intake passage upstream of the compressor;
EGR control means for performing EGR by using or switching the high pressure EGR means and the low pressure EGR means in accordance with the operating state of the internal combustion engine;
Water temperature measuring means for measuring the cooling water temperature of the internal combustion engine;
With
The EGR control means makes the ratio of the exhaust gas flowing into the internal combustion engine by the low pressure EGR means occupying the exhaust gas flowing into the internal combustion engine variable according to the cooling water temperature measured by the water temperature measuring means. EGR system for internal combustion engines. In claim 6,
The EGR system for an internal combustion engine, wherein the EGR control means reduces the ratio of exhaust gas flowing into the internal combustion engine by the low pressure EGR means that occupies the exhaust gas flowing into the internal combustion engine as the cooling water temperature decreases.

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