JP2011001893A - Exhaust gas purification system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purification system capable of returning the exhaust gas through a return path from the downstream side of the exhaust gas to the air intake side in the exhaust gas purification device without damaging the device mounted in the return flow path when the temperature of the exhaust gas on the downstream side of the exhaust gas of the exhaust gas purification device is increased during the regeneration of the exhaust gas purification device and the like.SOLUTION: When post-injection is carried out to regenerate a DPF 50, an ECU 80 closes a high pressure EGR valve 42 to prohibit an EGR gas from flowing into a high pressure return flow path 220 and opens a low pressure EGR valve 62 in place of the high pressure EGR valve 42 to return the EGR gas through the low pressure return flow path 230 from the exhaust emission side to the air intake side. The ECU 80 controls the opening degree of the low pressure EGR valve 62 based on the exhaust gas temperature on the downstream side of the exhaust gas of the DPF 50 and the quantity of the EGR gas flowing in the low pressure return flow path 230 to adjust the quantity of the EGR gas flowing in the low pressure return flow path 230 to prevent the damage of a low pressure EGR cooler 60 and the low pressure EGR valve 62 due to the heat of the EGR gas.

Description

  The present invention relates to an exhaust gas purification system in which exhaust gas is recirculated from an exhaust downstream side to an intake side of an exhaust purification device that is installed in an exhaust flow path to remove harmful components in the exhaust gas, and the recirculation amount of the exhaust gas is adjusted by a recirculation amount adjustment valve. About.

  Conventionally, it has been known that exhaust gas recirculation (EGR) that recirculates exhaust gas from an exhaust side to an intake side of an internal combustion engine suppresses combustion in a cylinder of the internal combustion engine and reduces NOx emission. Exhaust gas (also referred to as EGR gas) recirculated from the exhaust side to the intake side through the recirculation flow path connecting the exhaust side and the intake side is cooled by the EGR cooler and the flow rate is adjusted by the EGR valve ( For example, see Patent Document 1). By reducing the temperature of the EGR gas with the EGR cooler, the combustion temperature in the cylinder is lowered and combustion is further suppressed, and more exhaust gas with a larger mass can be recirculated with the same amount of EGR gas. .

  By the way, in Patent Document 1, in order to purify harmful components removed by the exhaust purification device, unburned components are added to the exhaust passage by post injection or the like, and the unburned components undergo an oxidation reaction with an oxidation catalyst or the like. Heat is used to clean up harmful components.

  In this case, in the configuration in which the EGR gas is recirculated from the exhaust upstream side of the exhaust purification device to the intake side, the device installed in the recirculation flow path such as the EGR valve or the EGR cooler is wetted by the unburned components added to the exhaust flow path. , It becomes easy for the particulates in the EGR gas to adhere. For example, if particulates adhere to the valve portion of the EGR valve, the valve portion may stick, or there may be a gap when fully closed due to the particulate adhering to the valve portion, and EGR gas may leak from the valve portion. Moreover, if particulates adhere in the EGR cooler, the cooling efficiency of the EGR cooler decreases.

With respect to this problem, in Patent Document 1, when an unburned component is added to the exhaust flow path to regenerate the exhaust purification device, the EGR valve is closed so that EGR gas does not flow through the recirculation flow path.
However, since the EGR gas cannot be recirculated to the intake side when the EGR valve is closed, there arises a problem that the NOx emission amount cannot be reduced during regeneration of the exhaust purification device.

  Therefore, it is conceivable to recirculate the EGR gas not from the exhaust upstream side of the exhaust purification device but from the exhaust downstream side to the intake side. In this configuration, even if unburned components are added for regeneration of the exhaust purification device, the unburned components undergo an oxidation reaction by the oxidation catalyst carried on the exhaust upstream side of the exhaust purification device or on the exhaust purification device itself. Unburned components do not flow out to the exhaust downstream side of the exhaust purification device.

  This prevents the EGR valve and the EGR cooler from getting wet with unburned components even when the EGR gas is recirculated from the exhaust downstream side of the exhaust purification device through the recirculation flow path to the intake side during regeneration of the exhaust purification device. . Since the EGR gas can be recirculated to the intake side during regeneration of the exhaust purification device, the NOx emission amount can be reduced.

JP 2005-299480 A

  However, in the configuration in which the EGR gas is recirculated from the exhaust downstream side of the exhaust purification device to the intake side, the unburned component added during regeneration of the exhaust purification device undergoes an oxidation reaction, so that the exhaust gas on the exhaust downstream side of the exhaust purification device The temperature rises, and the EGR gas whose temperature has risen passes through the reflux channel. Then, there is a possibility that the devices installed in the reflux flow path such as the EGR valve and the EGR cooler may be damaged by heat.

The rise in the exhaust gas temperature at the exhaust gas downstream side of the exhaust gas purification device occurs not only due to the oxidation reaction of unburned components, but also when the particulates collected in the exhaust gas purification device burn.
If the EGR valve is closed during regeneration of the exhaust purification device in order to prevent the device installed in the reflux flow path from being damaged by heat, as described above, NOx generated during regeneration of the exhaust purification device. There is a problem that cannot be reduced.

  The present invention has been made to solve the above problem, and when the exhaust gas temperature on the exhaust downstream side of the exhaust gas purification device rises during regeneration of the exhaust gas purification device, the device installed in the recirculation flow path is damaged. It is an object of the present invention to provide an exhaust purification system that can recirculate exhaust gas through a recirculation flow path from the exhaust downstream side of the exhaust purification device to the intake side without performing the above.

  According to the invention described in claims 1 to 18, the recirculation flow path recirculates the exhaust gas downstream of the exhaust purification device to the intake side, and the recirculation amount adjustment valve is installed in the recirculation flow path to recirculate from the exhaust side to the intake side. The amount of exhaust gas recirculated is adjusted.

  As a result, even if unburned components are added to the exhaust flow path in order to regenerate the exhaust purification device, the unburned components are consumed by the oxidation reaction, etc., so the unburned components are discharged to the exhaust downstream side of the exhaust purification device. Not. As a result, even if the exhaust gas flows through the recirculation channel by opening the recirculation amount adjustment valve during regeneration of the exhaust purification device, the device installed in the recirculation channel including the recirculation amount adjustment valve gets wet with unburned components. Can be prevented.

  Further, according to the invention described in claims 1 to 18, the recirculation temperature detecting means detects the recirculation temperature of the exhaust gas recirculated from the exhaust side to the intake side through the recirculation flow path, and the recirculation amount control means comprises the recirculation temperature control means. Based on the reflux temperature detected by the detection means, the reflux amount adjustment valve is controlled to adjust the reflux amount.

  Thus, for example, when the exhaust gas temperature rises due to an oxidation reaction of unburned components added for the regeneration of the exhaust gas purification device, the recirculation amount of the exhaust gas is adjusted based on the recirculation temperature of the exhaust gas flowing through the recirculation passage Therefore, it is possible to prevent the device installed in the reflux flow path including the reflux amount adjusting valve from being exposed to a large amount of exhaust gas at a high temperature.

  As a result, even when the exhaust gas temperature on the exhaust gas downstream side of the exhaust gas purification device rises, for example, during regeneration of the exhaust gas purification device, the device installed in the recirculation flow path is prevented from being damaged by the heat of the EGR gas. The exhaust gas can be recirculated as much as possible from the exhaust downstream side of the purification device to the intake side.

  According to the invention of claim 2, the recirculation amount detection means detects the recirculation amount of the exhaust gas recirculated from the exhaust side to the intake side through the recirculation flow path, and the recirculation amount control means detects the recirculation temperature detection means. Based on the reflux temperature and the reflux amount detected by the reflux amount detection means, the reflux amount adjustment valve is controlled to adjust the reflux amount.

  Thus, since the recirculation amount of the EGR gas is adjusted based on the flow rate in addition to the temperature of the EGR gas, it is possible to prevent the device installed in the recirculation flow path from being damaged by the thermal energy of the EGR gas with higher accuracy.

  By the way, the volume of gas sucked into the cylinder can be calculated by the product of the cylinder volume of the internal combustion engine and the rotational speed of the internal combustion engine. Then, based on the volume of gas sucked into the cylinder and the intake pressure and intake temperature in the intake manifold, the total number of moles of gas sucked into the cylinder can be calculated from the gas state equation. The total number of moles of gas sucked into the cylinder is the sum of the number of moles calculated from the intake air amount detected from the intake air amount sensor and the number of moles of EGR gas recirculated from the exhaust side to the intake side.

  Therefore, according to the third aspect of the invention, the recirculation amount detection means estimates the recirculation amount based on the intake pressure and intake temperature of the intake manifold, the rotational speed of the internal combustion engine, and the intake amount, and detects it as the recirculation amount. To do.

  Thus, the total number of moles of gas sucked into the cylinder is calculated based on the intake pressure and temperature of the intake manifold and the rotational speed of the internal combustion engine, and the mole calculated from the intake amount with respect to the total number of moles. By subtracting the number, the amount of exhaust gas recirculation can be estimated.

According to the fourth aspect of the invention, the reflux amount control means controls the reflux amount adjustment valve to reduce the reflux amount as the reflux amount detected by the reflux amount detection means increases.
If the reflux temperature is the same, the greater the amount of reflux, the greater the thermal energy of the EGR gas. Therefore, as the amount of reflux detected by the reflux amount detection means increases, the amount of reflux is reduced so that it is installed in the reflux channel. The thermal energy received from the EGR gas is reduced. Thereby, it can prevent that the apparatus installed in the recirculation flow path is damaged by the thermal energy of EGR gas.

According to the fifth aspect of the present invention, the recirculation temperature detection means detects the recirculation temperature based on the exhaust gas temperature on the exhaust downstream side of the exhaust gas purification device.
Since there is usually no factor that increases the reflux temperature, which is the temperature of the EGR gas, on the exhaust downstream side of the exhaust purification device, the reflux temperature can be detected with high accuracy based on the exhaust temperature on the exhaust downstream side of the exhaust purification device.

  According to the sixth aspect of the present invention, the exhaust purification device includes a filter that collects particulates in the exhaust gas, and the recirculation temperature detection means includes the exhaust gas temperature upstream of the exhaust purification device and the exhaust gas of the exhaust purification device. At least exhaust gas purification among the unburned component concentration on the upstream side, the oxygen concentration on the upstream side of the exhaust purification device, the amount of exhaust gas flowing into the exhaust purification device, and the amount of particulates collected by the exhaust purification device Estimate the exhaust gas temperature downstream of the exhaust gas purification device based on the exhaust gas temperature upstream of the device, the unburned component concentration upstream of the exhaust gas purification device, and the amount of exhaust gas flowing into the exhaust gas purification device. The recirculation temperature is detected based on the estimated exhaust gas temperature.

  Thereby, the amount of heat generated when the unburned component undergoes an oxidation reaction can be calculated based on the unburned component concentration. The exhaust gas temperature downstream of the exhaust gas purification apparatus can be estimated based on the amount of heat, the exhaust gas temperature of the exhaust gas flowing into the exhaust gas purification apparatus, and the exhaust gas quantity flowing into the exhaust gas purification apparatus. The higher the concentration of unburned components, the higher the exhaust temperature of the exhaust gas flowing into the exhaust purification device, and the lower the amount of exhaust gas flowing into the exhaust purification device, the higher the exhaust temperature downstream of the exhaust purification device. .

  Note that when the oxygen concentration is low, some of the unburned components may not undergo an oxidation reaction, so the amount of heat generated when the unburned components undergo an oxidation reaction may be estimated in consideration of the oxygen concentration. Depending on the amount of particulates collected in the filter, the exhaust downstream side of the exhaust gas purifying device takes into account the amount of heat generated when the particulates burn in addition to the amount of heat generated by the oxidation reaction of unburned components. The temperature may be estimated.

  By the way, the particulates collected in the exhaust purification device are combusted even when no unburned components are added, for example, when the amount of fuel injection into the cylinder increases and the exhaust gas temperature flowing into the exhaust purification device rises. Sometimes. The amount of heat generated when the particulates burn can be calculated based on the amount of particulates collected in the exhaust purification device.

  Based on the amount of heat generated when the particulates burn, the exhaust gas temperature of the exhaust gas flowing into the exhaust gas purification device, and the exhaust gas amount flowing into the exhaust gas purification device, the exhaust gas temperature downstream of the exhaust gas purification device is estimated. it can. Further, the exhaust gas temperature at the exhaust downstream side of the exhaust purification device becomes higher as the particulate amount is larger, the exhaust temperature of the exhaust gas flowing into the exhaust purification device is higher, and the exhaust gas amount flowing into the exhaust purification device is smaller.

  Therefore, according to the seventh aspect of the present invention, the exhaust gas purification device includes a filter that collects particulates in the exhaust gas, and the recirculation temperature detection means includes the exhaust gas temperature upstream of the exhaust gas purification device, the exhaust gas purification device, and the exhaust gas purification device. Of the unburned component concentration upstream of the exhaust gas, the oxygen concentration upstream of the exhaust purification device, the amount of exhaust gas flowing into the exhaust purification device, and the amount of particulates collected by the exhaust purification device Based on the exhaust temperature upstream of the exhaust purification device, the amount of exhaust gas flowing into the exhaust purification device, and the amount of particulates collected by the exhaust purification device, the exhaust temperature downstream of the exhaust purification device is determined. The recirculation temperature is detected based on the estimated exhaust gas temperature.

  When the oxygen concentration is low, some of the particulates collected in the exhaust gas purification device may not burn, so the amount of heat generated when the particulates burn is estimated using the oxygen concentration as a parameter. May be. When an unburned component is added, the amount of heat generated by the oxidation reaction of the unburned component may be estimated using the concentration of the unburned component as a parameter.

According to the eighth aspect of the present invention, the recirculation temperature detecting means detects the recirculation temperature based on the exhaust gas temperature on the exhaust downstream side of the exhaust purification device detected by the downstream temperature sensor.
As a result, the exhaust gas temperature downstream of the exhaust gas purification apparatus can be detected directly and with high accuracy without estimating the exhaust gas temperature downstream of the exhaust gas purification apparatus.

According to the ninth aspect of the invention, the recirculation amount control means controls the recirculation amount adjustment valve to reduce the recirculation amount as the recirculation temperature detected by the recirculation temperature detection means increases.
As described above, since the amount of reflux is reduced as the reflux temperature increases, it is possible to prevent the device installed in the reflux channel from being damaged by heat.

According to the invention described in claim 10, the exhaust gas recirculated from the exhaust side to the intake side is cooled by the exhaust cooling device installed in the recirculation flow path.
As a result, the combustion temperature in the cylinder is lowered and combustion is suppressed, and if the EGR gas amount is the same, a larger amount of exhaust gas can be recirculated. As a result, it is possible to reduce the amount of NOx discharged from the cylinder.

  Moreover, since the exhaust cooling device has cooling fins or the like for cooling the EGR gas, the exhaust cooling device is easily damaged by heat. Therefore, adjusting the recirculation amount of the exhaust gas based on the recirculation temperature of the exhaust gas flowing through the recirculation flow path to prevent the exhaust cooling device from being exposed to a large amount of exhaust gas at a high temperature can prevent damage to the exhaust cooling device. It is effective.

According to the eleventh aspect of the present invention, the recirculation temperature detecting means detects the exhaust temperature on the exhaust upstream side of the exhaust cooling device as the recirculation temperature.
Accordingly, the exhaust gas recirculation amount can be adjusted based on the exhaust temperature upstream of the exhaust cooling device so that the exhaust cooling device is not damaged by heat.

  By the way, the temperature decrease amount of the exhaust temperature that is decreased until the exhaust gas reaches the exhaust upstream side of the exhaust cooling device from the exhaust downstream side of the exhaust purification device depends on the exhaust temperature and the recirculation amount on the exhaust downstream side of the exhaust purification device. Change.

  Therefore, according to the twelfth aspect of the present invention, the recirculation temperature detection means is configured to detect the exhaust gas upstream side of the exhaust cooling device based on the exhaust gas temperature on the exhaust gas downstream side of the exhaust gas purification device and the recirculation amount detected by the recirculation amount detection means. The exhaust temperature is estimated and detected as the reflux temperature.

  As a result, the temperature decrease amount of the exhaust temperature that is decreased until the exhaust gas reaches the exhaust upstream side of the exhaust cooling device from the exhaust downstream side of the exhaust purification device to the exhaust temperature and the recirculation amount on the exhaust downstream side of the exhaust purification device. Can be estimated.

  By the way, the amount of temperature decrease of the exhaust gas temperature that is decreased until the exhaust gas reaches the exhaust gas upstream side of the exhaust gas cooling device from the exhaust gas downstream side of the exhaust gas purification device becomes larger as the exhaust gas temperature on the exhaust gas downstream side of the exhaust gas purification device becomes higher. The smaller the flow rate, the smaller.

  Therefore, according to the invention described in claim 13, the temperature reduction amount estimation means for estimating the temperature reduction amount of the exhaust temperature from the exhaust downstream side of the exhaust purification device to the exhaust upstream side of the exhaust cooling device is the recirculation amount detection means. As the amount of recirculation detected increases, the temperature decrease amount is estimated to decrease, and as the exhaust gas temperature on the exhaust downstream side of the exhaust purification device increases, the temperature decrease amount is estimated to increase. The recirculation temperature detecting means subtracts the temperature decrease amount estimated by the temperature decrease amount estimating means from the exhaust gas downstream temperature of the exhaust gas purification device to calculate the exhaust gas upstream temperature of the exhaust air cooling device to obtain the recirculation temperature. To detect.

As a result, the exhaust gas temperature on the exhaust gas upstream side of the exhaust gas cooling device can be estimated and detected with high accuracy based on the exhaust gas temperature and the recirculation amount on the exhaust gas downstream side of the exhaust gas purification device.
According to the fourteenth aspect of the present invention, the recirculation temperature detecting means further includes the exhaust upstream side of the exhaust cooling device based on the time delay characteristic of the exhaust temperature from the exhaust downstream side of the exhaust purification device to the exhaust upstream side of the exhaust cooling device. Is detected as the reflux temperature.

  As a result, the exhaust upstream of the exhaust cooling device changes with a delay from the exhaust temperature on the exhaust downstream side of the exhaust purification device in consideration of the flow path length or flow resistance of the return flow channel from the exhaust purification device to the exhaust cooling device. The side temperature can be estimated with high accuracy.

  According to the invention described in claim 15, the recirculation temperature detecting means detects the exhaust gas temperature on the exhaust upstream side of the exhaust cooling device detected by the upstream temperature sensor installed on the exhaust upstream side of the exhaust cooling device as the recirculation temperature. .

As a result, the exhaust temperature on the exhaust upstream side of the exhaust cooling device can be detected directly and with high accuracy without estimating the exhaust temperature on the exhaust upstream side of the exhaust cooling device.
According to the sixteenth aspect of the present invention, when the reflux temperature detected by the reflux temperature detection means is equal to or higher than a predetermined value, the reflux amount control means controls the reflux quantity adjustment valve to adjust the reflux quantity.

  Thereby, when the reflux temperature is equal to or higher than a predetermined value, the reflux amount is adjusted. When the reflux temperature is lower than the predetermined value, for example, the reflux amount adjustment valve can be fully opened. As a result, it is possible to reduce the control load for the recirculation amount control means to control the recirculation amount adjustment valve.

  According to the invention described in claim 17, the exhaust gas purifying device includes a filter that collects particulates in the exhaust gas, and the oxidation catalyst is supported on the filter itself or installed on the exhaust upstream side of the filter. Is provided.

  As described above, in the configuration in which the oxidation catalyst is supported on the filter itself that collects the particulates as the exhaust purification device or the oxidation catalyst is installed on the exhaust upstream side of the filter, the exhaust purification device collects the exhaust catalyst. When the amount of particulates increases and the pressure loss of the exhaust purification device increases, unburned components are added to the exhaust passage.

  When the added unburned component is oxidized by the oxidation catalyst and the exhaust temperature rises, the particulates collected by the exhaust purification device are burned, and the exhaust purification device is regenerated. Thus, when the exhaust purification device is regenerated, the temperature on the exhaust downstream side of the exhaust purification device rises.

  Therefore, in the configuration in which the unburned component is added and the particulates collected by the exhaust purification device are burned, the timing at which the unburned component is added is known, so the timing at which the unburned component is added and the exhaust temperature rises The reflux flow rate can be adjusted appropriately according to

According to the eighteenth aspect of the present invention, the exhaust gas purification apparatus includes the NOx catalyst that removes NOx components in the exhaust gas.
Since the NOx catalyst usually carries an oxidation catalyst such as platinum, when an unburned component is added, the unburned component is oxidized by the oxidation catalyst and the exhaust temperature rises. And since the timing which an unburned component is added is known, a recirculation flow rate can be adjusted appropriately according to the timing which an unburned component is added and exhaust temperature rises.

  The functions of the plurality of means provided in the present invention are realized by hardware resources whose functions are specified by the configuration itself, hardware resources whose functions are specified by a program, or a combination thereof. The functions of the plurality of means are not limited to those realized by hardware resources that are physically independent of each other.

The block diagram which shows the exhaust gas purification system by 1st Embodiment. The time chart which shows the temperature change of DPF downstream at the time of DPF reproduction | regeneration. The characteristic view which shows the relationship between a recirculation amount detection value, DPF downstream side temperature, and a recirculation amount upper limit. (A) is a time chart showing a delay characteristic of the exhaust temperature from the downstream side of the DPF to the upstream side of the EGR cooler, and (B) is a characteristic chart showing the relationship between the reflux amount, the DPF downstream side temperature, and the temperature decrease amount of the reflux temperature. 5 is a flowchart showing an EGR gas amount control routine 1; 7 is a flowchart showing an EGR gas amount control routine 2; The block diagram which shows the exhaust gas purification system by 2nd Embodiment. The block diagram which shows the exhaust gas purification system by 3rd Embodiment. The block diagram which shows the exhaust gas purification system by 4th Embodiment. The block diagram which shows the exhaust gas purification system by 5th Embodiment.

Hereinafter, the embodiments of the present invention will be described with reference to FIG.
[First Embodiment]
An exhaust purification system according to a first embodiment of the present invention is shown in FIG.

(Exhaust gas purification system 10)
The exhaust purification system 10 according to the first embodiment is a system in which fuel injected from a fuel injection valve 4 is burned by a diesel engine (hereinafter also simply referred to as “engine”) 2 and exhaust gas discharged from the engine 2 is purified. It is. Engine 2 is, for example, a four-cylinder internal combustion engine. In the present embodiment, exhaust gas recirculates from the exhaust side to the intake side in two systems of the high pressure recirculation flow path 220 and the low pressure recirculation flow path 230.

  Foreign matter is removed from the intake air drawn into the intake flow path 200 by the air cleaner 12, and the intake air amount is detected by the intake air amount sensor 14. The intake air amount sensor 14 is installed upstream of the position where the high pressure recirculation flow path 220 and the low pressure recirculation flow path 230 are connected to the intake flow path 200. That is, the intake air amount detected by the intake air amount sensor 14 is the intake air amount before the EGR gas is recirculated from the exhaust side to the intake side.

  The intake air compressed by the compressor 32 of the turbocharger 30 is cooled by the intercooler 16. The compressor 32 is rotationally driven via a shaft by a turbine 34 installed in the exhaust passage 210.

  The intake air cooled by the intercooler 16 is adjusted in flow rate by the throttle valve 18. The throttle valve 18 is throttled to allow more EGR gas to enter in the light load region, but is kept almost fully open in the high load region in order to increase the intake air amount and reduce pumping loss.

  The intake air that has passed through the throttle valve 18 is branched by the intake manifold 20 and is drawn into each cylinder of the engine 2. The intake manifold 20 is provided with an intake pressure sensor 22 and an intake air temperature sensor 24, respectively.

  The intake flow path 200 and the exhaust flow path 210 are connected by a high pressure recirculation flow path 220 and a low pressure recirculation flow path 230, respectively, and exhaust gas passes from the exhaust side to the intake side through the high pressure recirculation flow path 220 and the low pressure recirculation flow path 230. Refluxed. The high pressure recirculation flow path 220 connects the exhaust flow path 210 between the engine 2 and the turbine 34 of the turbocharger 30 and the intake manifold 20. The low pressure recirculation flow path 230 connects the exhaust flow path 210 on the exhaust downstream side of the DPF (Diesel Particulate filter) 50 and the intake flow path 200 between the intake air amount sensor 14 and the compressor 32 of the turbocharger 30. .

  Since the position where the high pressure recirculation flow path 220 is connected to the intake flow path 200 in the intake manifold 20 is the intake air downstream side of the compressor 32 of the turbocharger 30, the intake pressure at the position where the high pressure recirculation flow path 220 is connected to the intake flow path 200. Is higher than the position where the low pressure recirculation flow path 230 is connected to the intake flow path 200 on the intake upstream side of the compressor 32 of the turbocharger 30.

  A high pressure EGR cooler 40 and a high pressure EGR valve 42 are installed in this order from the exhaust side in the high pressure reflux passage 220. The high-pressure EGR cooler 40 is formed, for example, in a stacked structure in which thin plates extending from the exhaust upstream side toward the downstream side are stacked at a predetermined interval. Between the thin plates, layers in which cooling water flows and layers in which wavy fins are installed are alternately formed. The layer in which the fins are installed forms a cooling channel.

  The high pressure EGR valve 42 is an electromagnetic valve whose opening degree is controlled by the duty ratio or the amount of supplied power. By controlling the opening degree of the high-pressure EGR valve 42, the amount of EGR gas, which is the amount of exhaust gas recirculated from the exhaust side to the intake side through the high-pressure recirculation passage 220, is adjusted.

  The DPF 50 is installed on the exhaust downstream side of the turbine 34 of the turbocharger 30. The DPF 50 is formed of a honeycomb structure in which an oxidation catalyst such as platinum is supported on a porous ceramic. The inlet side and the outlet side of the flow path formed in the exhaust flow direction of the honeycomb structure of the DPF 50 are alternately sealed. Particulates, which are harmful components in the exhaust gas, flow in from the flow path in which the inlet side is not sealed and the outlet side is sealed, and when the particulates pass through the partition walls of the honeycomb structure forming the flow path, It is collected in the hole. And exhaust gas flows out of the flow path with which the inlet side is sealed and the outlet side is not sealed.

  Exhaust temperature sensors 52 and 54 are installed on the exhaust upstream side and downstream side of the DPF 50, respectively. The differential pressure sensor 56 detects a differential pressure between the exhaust inlet and the exhaust outlet of the DPF 50. When the amount of particulates collected by the DPF 50 increases, the differential pressure detected by the differential pressure sensor 56 increases. Therefore, the particulate amount collected by the DPF 50 can be estimated based on the differential pressure detected by the differential pressure sensor 56.

  A low pressure EGR cooler 60 and a low pressure EGR valve 62 are installed in this order from the exhaust side in the low pressure reflux passage 230. The low-pressure EGR cooler 60 and the low-pressure EGR valve 62 have substantially the same configuration as the high-pressure EGR cooler 40 and the high-pressure EGR valve 42 described above, respectively, although there are differences in physique.

  The low pressure EGR cooler 60 cools the EGR gas that is recirculated from the exhaust side to the intake side through the low pressure recirculation flow path 230. Further, by controlling the opening degree of the low pressure EGR valve 62, the amount of EGR gas that is the recirculation amount of the exhaust gas recirculated from the exhaust side to the intake side through the low pressure recirculation passage 230 is adjusted.

  The ECU 80 is mainly composed of a microcomputer (not shown) having a CPU, RAM, ROM, flash memory, communication interface, and the like. The ECU 80 controls the engine operating state by the CPU executing a control program stored in a storage device such as a ROM or a flash memory of the ECU 80.

  The ECU 80 outputs signals from the intake air amount sensor 14, the intake pressure sensor 22, the intake air temperature sensor 24, the exhaust gas temperature sensors 52 and 54, the differential pressure sensor 56, the engine speed sensor 70, the accelerator opening sensor 72, and other various sensors. The engine operating state is acquired from Then, the ECU 80 controls the injection timing and the injection amount of the fuel injection valve 4 based on the acquired engine operating state. Further, the ECU 80 includes main injection that generates the main torque of the engine based on the engine operating state, and performs multi-stage injection such as pilot injection before the main injection and post injection after the main injection.

  The pilot injection is performed so that air and a small amount of fuel are mixed in advance before ignition by the main injection. The post-injection is performed to inject a minute amount of fuel and burn the particulates collected by the DPF 50.

Further, the ECU 80 adjusts the amount of EGR gas that recirculates from the exhaust side to the intake side by controlling the opening degree of the high pressure EGR valve 42 and the low pressure EGR valve 62.
(Switching EGR control)
Next, switching between use of the high-pressure reflux channel 220 and the low-pressure reflux channel 230 will be described. As described above, the high-pressure recirculation flow path 220 recirculates EGR gas from the exhaust side into the intake manifold 20 which is the intake flow path 200 on the downstream side of the compressor 32 of the turbocharger 30. Since the EGR gas is sucked into the intake side due to the differential pressure between the exhaust side and the intake side, when the engine operating state is a high load state and the supercharging pressure of the turbocharger 30 is high, the high pressure There are times when it is difficult to recirculate the EGR gas from the exhaust side to the intake side through the recirculation flow path 220.

  On the other hand, the low pressure recirculation flow path 230 recirculates EGR gas from the exhaust side to the intake flow path 200 on the upstream side of the compressor 32 whose intake pressure is lower than that on the downstream side of the compressor 32 of the turbocharger 30. Therefore, even when the engine operation state is a high load state, the EGR gas can be recirculated from the exhaust side to the intake side through the low pressure recirculation flow path 230.

  Therefore, in a high load operation state, the low pressure EGR valve 62 is opened, and the EGR gas is recirculated from the exhaust side to the intake side through the low pressure recirculation flow path 230. In this case, the high pressure EGR valve 42 is closed in order to adjust the amount of EGR gas recirculated from the exhaust side to the intake side with high accuracy.

  However, when the engine operating state is other than the high load state, the high pressure EGR valve 42 is opened, and the EGR gas is recirculated from the exhaust side to the intake side through the high pressure recirculation flow path 220. In this case, the low pressure EGR valve 62 is closed in order to adjust the amount of EGR gas recirculated from the exhaust side to the intake side with high accuracy.

  Further, when post injection is performed to regenerate the DPF 50 by burning the particulates collected by the DPF 50, the post injection is performed when the high pressure EGR valve 42 is opened and the EGR gas flows through the high pressure reflux passage 220. As a result, the unburned component added to the exhaust passage 210 adheres to the high pressure EGR cooler 40 and the high pressure EGR valve 42, and the high pressure EGR cooler 40 and the high pressure EGR valve 42 are wetted by the unburned component.

  Then, the particulates in the EGR gas adhere to the cooling fins of the high pressure EGR cooler 40, and the cooling efficiency of the high pressure EGR cooler 40 decreases. Further, if particulates in the EGR gas adhere to the valve portion of the high-pressure EGR valve 42, the valve portion may be fixed, or the particulates may bite into the valve portion, so that the EGR gas may leak from the valve portion when fully closed. .

  Therefore, when post injection is being performed for regeneration of the DPF 50, the high pressure EGR valve 42 is closed to prohibit the EGR gas from flowing into the high pressure reflux passage 220. Then, the low pressure EGR valve 62 is opened instead of the high pressure EGR valve 42, and the EGR gas is recirculated from the exhaust side to the intake side through the low pressure recirculation passage 230.

  The unburned components added to the exhaust flow path 210 by the post injection are oxidized by the oxidation catalyst supported on the DPF 50 and are not discharged to the exhaust downstream side of the DPF 50. Since the low pressure recirculation flow path 230 recirculates the EGR gas from the exhaust downstream side of the DPF 50 to the intake side, the EGR gas flowing through the low pressure recirculation flow path 230 even if the low pressure EGR valve 62 is opened during regeneration of the DPF 50. Does not contain unburned components. Therefore, even if an unburned component is added to the exhaust passage 210 for regeneration of the DPF 50, the low pressure EGR cooler 60 and the low pressure EGR valve 62 are not wetted by the unburned component.

  By the way, when unburned components are added to the exhaust flow path 210 by post injection and the unburned components are oxidized in the DPF 50, the exhaust temperature on the exhaust downstream side of the DPF 50 rises due to reaction heat. In this case, when the post-injection amount is appropriate or the particulates collected in the DPF 50 burn in a normal state, the exhaust temperature downstream of the DPF 50 is as shown by the solid line 300 in FIG. The temperature is appropriately raised within the allowable range.

  On the other hand, for example, when a large amount of particulate matter collected in the DPF 50 is burnt rapidly due to a rise in the exhaust temperature even when the post injection amount is large or when the post injection is not performed, the exhaust downstream of the DPF 50 As shown by the dotted line 310 in FIG. 2, the exhaust temperature on the side may exceed the upper limit value of the exhaust temperature and rise excessively.

If the low-pressure EGR valve 62 is opened when the exhaust gas temperature on the exhaust gas downstream side of the DPF 50 is excessively high, high-temperature EGR gas flows from the downstream side of the DPF 50 to the low-pressure recirculation passage 230. As a result, the devices such as the low pressure EGR cooler 60 and the low pressure EGR valve 62 installed in the low pressure recirculation flow path 230 may be damaged by heat (exhaust temperature detection on the exhaust downstream side of the DPF 50).
Therefore, in this embodiment, the exhaust temperature on the exhaust downstream side of the DPF 50 is detected by the exhaust temperature sensor 54 installed on the exhaust downstream side of the DPF 50, and the opening degree of the low pressure EGR valve 62 is controlled using the detected exhaust temperature as the reflux temperature. As a result, the amount of EGR gas flowing through the low pressure reflux channel 230 is adjusted. By directly detecting the exhaust gas temperature downstream of the DPF 50 by the exhaust gas temperature sensor 54, the exhaust gas temperature downstream of the DPF 50 can be detected with high accuracy.

  For example, as shown in FIG. 3, as the exhaust gas temperature on the exhaust downstream side of the DPF 50 becomes higher, the opening degree of the low pressure EGR valve 62 is made smaller and the upper limit value of the amount of EGR gas flowing through the low pressure recirculation flow path 230 is made smaller. Reduce gas volume. On the other hand, as the exhaust gas temperature on the downstream side of the DPF 50 becomes lower, the upper limit value of the amount of EGR gas flowing through the low pressure recirculation flow path 230 is increased and the opening degree of the low pressure EGR valve 62 is increased to increase the EGR gas amount. Thereby, it is possible to prevent the low pressure EGR cooler 60 and the low pressure EGR valve 62 installed in the low pressure reflux flow path 230 from being damaged by heat.

  Instead of using the exhaust temperature sensor 54, the exhaust temperature on the exhaust downstream side of the DPF 50 may be estimated and detected based on the engine operating state. For example, based on the exhaust gas temperature upstream of the DPF 50, the concentration of unburned components upstream of the DPF 50, and the amount of exhaust gas flowing into the DPF 50, the exhaust temperature that rises due to the oxidation reaction of the unburned components in the DPF 50 Can be estimated. This estimated temperature may be detected as the exhaust temperature on the exhaust downstream side of the DPF 50.

  The exhaust temperature on the exhaust upstream side of the DPF 50 is detected from the output signal of the exhaust temperature sensor 52 installed on the exhaust upstream side of the DPF 50. The unburned component concentration on the exhaust upstream side of the DPF 50 is calculated from a map or the like based on the engine speed and the accelerator opening. The amount of exhaust gas flowing into the DPF 50 can be obtained by calculating the amount of intake air taken into the engine 2 based on the intake pressure in the intake manifold 20, the intake air temperature, and the engine speed.

  As described above, based on the exhaust gas temperature upstream of the DPF 50, the concentration of unburned components upstream of the DPF 50, and the amount of exhaust gas flowing into the DPF 50, the unburned components increase in the DPF 50 due to an oxidation reaction. When estimating the exhaust gas temperature, the exhaust gas downstream side of the DPF 50 can be estimated with higher accuracy by considering the oxygen concentration upstream of the DPF 50 and the amount of particulates collected in the DPF 50.

  The oxygen concentration on the exhaust upstream side of the DPF 50 can be calculated from a map or the like based on the engine speed and the accelerator opening, similarly to the unburned component concentration on the exhaust upstream side of the DPF 50. The amount of particulates collected in the DPF 50 can be detected from the output signal of the differential pressure sensor 56.

  Even when unburned components are not added to the exhaust passage 210 and the DPF 50 is not being regenerated, the particulates collected in the DPF 50 are combusted due to the rise in the exhaust temperature, and the temperature of the DPF 50 on the downstream side of the exhaust becomes higher. May rise. In this case, the particulate matter collected by the DPF 50 rises by burning based on the exhaust gas temperature upstream of the DPF 50, the amount of particulates collected in the DPF 50, and the amount of exhaust gas flowing into the DPF 50. The exhaust temperature can be estimated. This estimated temperature may be detected as the exhaust temperature on the exhaust downstream side of the DPF 50.

  In this way, the particulates collected by the DPF 50 are burned based on the exhaust gas temperature upstream of the DPF 50, the amount of particulates collected in the DPF 50, and the amount of exhaust gas flowing into the DPF 50. When estimating the rising exhaust gas temperature, it is possible to estimate the exhaust gas temperature downstream of the DPF 50 with higher accuracy by considering the oxygen concentration upstream of the DPF 50 and the unburned component concentration upstream of the DPF 50. .

(EGR gas amount detection)
By the way, when the amount of EGR gas that is the recirculation amount of the exhaust gas flowing through the low pressure recirculation flow path 230 is large, the thermal energy of the EGR gas flowing through the low pressure recirculation flow path 230 becomes large. Therefore, the opening degree of the low pressure EGR valve 62 is controlled based on the amount of EGR gas flowing through the low pressure recirculation flow path 230 in addition to the exhaust gas temperature downstream of the DPF 50, and the amount of EGR gas flowing through the low pressure recirculation flow path 230 is adjusted. It is desirable. Control of the opening of the low pressure EGR valve 62 includes fully closing the opening of the low pressure EGR valve 62.

  For example, as shown in FIG. 3, as the amount of EGR gas flowing through the low-pressure recirculation flow path 230 (recirculation amount detection value) increases, the amount of EGR gas flowing through the low-pressure recirculation flow path 230 with the opening of the low-pressure EGR valve 62 decreased. Is reduced, and the amount of EGR gas is reduced. On the other hand, as the amount of EGR gas flowing through the low-pressure recirculation flow path 230 decreases, the opening degree of the low-pressure EGR valve 62 is increased to increase the upper limit value of the amount of EGR gas flowing through the low-pressure recirculation flow path 230, thereby increasing the EGR gas amount. .

  Here, the intake air amount sucked into the engine 2 is the sum of the intake air amount detected by the intake air amount sensor 14 and the EGR gas amount recirculated to the downstream side of the intake air amount sensor 14. Therefore, the EGR gas amount that is the recirculation amount of the exhaust gas flowing through the low pressure recirculation flow path 230 can be obtained by subtracting the intake air amount detected by the intake air amount sensor 14 from the intake air amount sucked into the engine 2.

  The intake air amount sucked into the engine 2 can be calculated based on the intake pressure in the intake manifold 20, the intake air temperature, and the engine speed. The pressure and temperature in the intake manifold 20 can be detected from the output signals of the intake pressure sensor 22 and the intake air temperature sensor 24 installed in the intake manifold 20, respectively.

(Exhaust temperature detection upstream of low pressure EGR cooler 60)
In order to prevent the low pressure EGR cooler 60 and the low pressure EGR valve 62 installed in the low pressure recirculation flow path 230 from being damaged by heat, the low pressure EGR cooler 60 close to the low pressure EGR cooler 60 and not on the exhaust downstream side of the DPF 50 is used. It is desirable to control the opening degree of the low-pressure EGR valve 62 based on the exhaust gas temperature upstream of the exhaust gas and adjust the amount of EGR gas flowing through the low-pressure recirculation flow path 230.

  The exhaust temperature on the exhaust upstream side of the low pressure EGR cooler 60 is determined based on the exhaust temperature on the exhaust downstream side of the DPF 50 detected from the output signal of the exhaust temperature sensor 54 installed on the exhaust downstream side of the DPF 50, or the engine operating state as described above. This can be estimated based on the estimated exhaust gas temperature downstream of the DPF 50.

However, as shown in FIG. 4A, there is a time delay in the exhaust temperature due to the pipe length, flow path resistance, etc., until the EGR gas reaches the low pressure EGR cooler 60 from the DPF 50.
Further, the exhaust temperature decreases due to heat conduction or the like until the EGR gas reaches the low pressure EGR cooler 60 from the DPF 50. As shown in FIG. 4B, the temperature decrease amount of the exhaust temperature increases as the exhaust gas temperature downstream of the DPF 50 increases, and decreases as the EGR gas amount as the recirculation amount increases.

  Therefore, considering such a time delay and the temperature decrease amount of the exhaust temperature, the exhaust gas upstream of the low pressure EGR cooler 60 is determined from the exhaust gas temperature downstream of the DPF 50 and the amount of EGR gas flowing through the low pressure recirculation passage 230. It is desirable to detect temperature. The exhaust gas temperature upstream of the low pressure EGR cooler 60 is subtracted from the exhaust gas temperature downstream of the DPF 50 from the temperature drop estimated from the exhaust gas temperature downstream of the DPF 50 and the amount of EGR gas flowing through the low pressure recirculation passage 230. This can be detected.

  The ECU 80 executes a control program stored in a ROM or a flash memory, thereby switching between opening and closing of the high pressure EGR valve 42 and the low pressure EGR valve 62 as described above. Switch the use of. When using the low pressure recirculation flow path 230, the EGR flowing through the low pressure recirculation flow path 230 is controlled by controlling the opening of the low pressure EGR valve 62 based on the exhaust gas temperature on the exhaust downstream side of the DPF 50 and the EGR gas amount. Adjust the gas volume.

(EGR gas amount control)
Next, control of the amount of EGR gas flowing through the low-pressure reflux channel 230 will be described based on the flowcharts shown in FIGS. The EGR gas amount control routine 1 shown in FIG. 5 and the EGR gas amount control routine 2 shown in FIG. 6 are always executed. "S" represents the step in FIGS. The ECU 80 may execute either the routine shown in FIG. 5 or FIG. 6 as the EGR gas amount control routine.

(EGR gas amount control routine 1)
In S400 of FIG. 5, as described above, the ECU 80 subtracts the intake air amount before the EGR gas detected by the intake air sensor 14 is recirculated to the intake side from the intake air amount sucked into the engine 2 to reduce the low pressure. The amount of EGR gas recirculated from the recirculation flow path 230 to the intake flow path 200 is detected as the recirculation amount.

  In S402, as described above, the ECU 80 determines the low pressure EGR cooler from the exhaust gas temperature on the downstream side of the DPF 50 and the amount of EGR gas flowing through the low pressure recirculation passage 230 based on the time delay and the temperature decrease amount related to the temperature of the EGR gas. The exhaust upstream temperature of 60 is detected as the reflux temperature.

  In S404, the ECU 80 controls the opening degree of the low pressure EGR valve 62 from the recirculation amount detected in S400 and the recirculation temperature detected in S402 based on the characteristic diagram of FIG. 3, and adjusts the upper limit value of the recirculation amount. This prevents the low-pressure EGR cooler 60 and the low-pressure EGR valve 62 from being damaged by the thermal energy of the EGR gas as devices installed in the low-pressure reflux channel 230.

(EGR gas amount control routine 2)
S410, S412, and S416 in FIG. 6 perform substantially the same processing as S400, S402, and S404 in FIG.

  In S414, the ECU 80 determines whether or not the reflux temperature detected in S412 is equal to or higher than a predetermined value. If the reflux temperature is equal to or higher than the predetermined value (S414: Yes), in S416, the ECU 80 controls the opening degree of the low pressure EGR valve 62 from the reflux amount and the reflux temperature, and adjusts the upper limit value of the reflux amount.

  If the recirculation temperature is lower than the predetermined value (S414: No), the ECU 80 determines that the low-pressure EGR cooler 60 and the low-pressure EGR valve 62 are not damaged by heat at the current recirculation temperature, and sets the opening of the low-pressure EGR valve 62. Without control, the opening degree of the low pressure EGR valve 62 remains the same or is fully opened, and the process returns to S410.

In the EGR gas amount control routine 2, since the opening degree of the low pressure EGR valve 62 is not controlled when the reflux temperature is lower than a predetermined value, the processing load of the ECU 80 can be reduced.
In the first embodiment, the engine 2 corresponds to the internal combustion engine of the present invention, the DPF 50 corresponds to the exhaust purification device and the filter of the present invention, the low pressure EGR cooler 60 corresponds to the exhaust cooling device of the present invention, and the low pressure EGR valve. 62 corresponds to the recirculation amount adjusting valve of the present invention, and the intake pressure sensor 22, the intake air temperature sensor 24, the engine speed sensor 70, and the intake air amount sensor 14 correspond to the recirculation amount detecting means of the present invention, and the exhaust temperature sensor 54. Corresponds to the reflux temperature detecting means and the downstream temperature sensor of the present invention, and the low pressure reflux channel 230 corresponds to the reflux channel of the present invention.

  Further, when the exhaust temperature on the exhaust downstream side of the DPF 50 is estimated and detected based on the engine operating state without using the exhaust temperature sensor 54, the exhaust temperature, the unburned component concentration, and the oxygen on the exhaust upstream side of the DPF 50 are detected. An exhaust temperature sensor 52, an engine speed sensor 70, an accelerator opening sensor 72, an intake pressure sensor 22, and the like for detecting the concentration, the amount of exhaust gas flowing into the DPF 50, and the amount of particulates collected in the DPF 50; The intake air temperature sensor 24 and the differential pressure sensor 56 correspond to the reflux temperature detecting means.

The ECU 80 functions as a recirculation temperature detection means, a recirculation amount detection means, a recirculation amount control means, and a temperature decrease amount estimation means based on the output signals of the various sensors.
Further, S400 in FIG. 5 and S410 in FIG. 6 correspond to the functions executed by the reflux amount detecting means, and S402 in FIG. 5 and S412 in FIG. 6 correspond to the functions executed by the reflux temperature detecting means and the temperature decrease amount estimating means. 5 and S414 and S416 in FIG. 6 correspond to the function executed by the reflux amount control means.

Second, third, fourth, fifth Embodiment]
Second, third, fourth, and fifth embodiments of the present invention are shown in FIGS. Components that are substantially the same as those in the first embodiment are denoted by the same reference numerals.

  In the exhaust purification system 100 of the second embodiment shown in FIG. 7, the low pressure EGR valve 62 is installed on the exhaust upstream side of the low pressure EGR cooler 60. In this configuration, since the low pressure EGR valve 62 is directly exposed to the EGR gas before being cooled by the low pressure EGR cooler 60, the thickness of the low pressure EGR valve 62 is increased in order to prevent damage to the low pressure EGR valve 62 due to heat. For example, it is necessary to improve the heat resistance of the low pressure EGR valve 62. Then, the size of the low pressure EGR valve 62 is increased, and as a result, the flow path area of the low pressure EGR valve 62 can be increased, so that the amount of EGR gas flowing through the low pressure recirculation flow path 230 can be increased.

  In the exhaust purification system 110 of the third embodiment shown in FIG. 8, only the low pressure recirculation flow path 230 is provided without providing the high pressure recirculation flow path 220. That is, EGR gas is recirculated only from the low pressure recirculation flow path 230 from the exhaust side to the intake side.

  In the third embodiment, the exhaust temperature sensor 64 is installed on the exhaust upstream side of the low pressure EGR cooler 60. Thus, the exhaust gas upstream side of the low pressure EGR cooler 60 is not estimated from the exhaust gas temperature downstream of the DPF 50 and the amount of EGR gas flowing through the low pressure recirculation flow path 230, but the exhaust gas upstream side of the low pressure EGR cooler 60. The exhaust gas temperature can be detected directly and with high accuracy based on the output signal of the exhaust gas temperature sensor 64.

In the third embodiment, the exhaust temperature sensor 64 corresponds to the upstream temperature sensor and the reflux temperature detection means of the present invention.
In the exhaust purification system 120 of the fourth embodiment shown in FIG. 9, an NOx storage reduction catalyst 90 is installed instead of the DPF 50. The NOx catalyst 90 is a device that stores NOx as a harmful component in exhaust gas in a fuel lean state and reduces the NOx stored in a fuel rich state.

  Also in this configuration, post injection is performed to reduce the NOx stored in the NOx catalyst 90 and regenerate the NOx catalyst. When the post-injection is executed and the unburned component is added to the exhaust passage 210, the unburned component is oxidized by the oxidation catalyst supported on the NOx catalyst 90 to generate heat, and the NOx catalyst 90 is activated. To do. Heat is also generated when the stored NOx is reduced.

  Accordingly, as in the first to third embodiments, when the unburned component is added and the NOx catalyst 90 is regenerated, the exhaust temperature on the downstream side of the NOx catalyst 90 rises. Therefore, the ECU 80 adjusts the EGR gas amount by controlling the opening degree of the low pressure EGR valve 62 based on the exhaust temperature downstream of the NOx catalyst 90 and the amount of EGR gas flowing through the low pressure recirculation passage 230.

In the fourth embodiment, the NOx catalyst 90 corresponds to the exhaust purification device of the present invention.
In the exhaust purification system 130 of the fifth embodiment shown in FIG. 10, in the configuration of the first embodiment, the low pressure EGR cooler 60 is not installed in the low pressure recirculation flow path 230 but only the low pressure EGR valve 62 is installed. Also in this configuration, in order to prevent the low pressure EGR valve 62 from being damaged by the heat of the EGR gas flowing through the low pressure reflux passage 230, the exhaust temperature downstream of the DPF 50 and the amount of EGR gas flowing through the low pressure reflux passage 230 are Based on this, the opening degree of the low pressure EGR valve 62 is controlled to adjust the EGR gas amount.

  In the above-described plurality of embodiments, in the exhaust purification system that recirculates the exhaust gas on the exhaust downstream side of the exhaust purification device such as the DPF 50 or the NOx catalyst 90 to the intake side through the low pressure recirculation passage 230, the low pressure recirculation passage The opening degree of the low-pressure EGR valve 62 is controlled based on the EGR gas temperature and the EGR gas amount flowing through 230, and the EGR gas amount flowing through the low-pressure recirculation passage 230 is adjusted.

  As a result, the reaction heat generated when the unburned component added to regenerate the exhaust purification device undergoes an oxidation reaction, or the exhaust temperature rises in a state where the unburned component is not added is collected in the DPF 50. Even if the EGR gas temperature rises due to combustion heat or the like generated by burning the particulates being burned, the low pressure EGR cooler 60 and the low pressure EGR valve 62 can be prevented from being damaged by heat.

[Other Embodiments]
In the above embodiment, the opening degree of the low-pressure EGR valve 62 is controlled based on both the EGR gas temperature and the EGR gas amount flowing through the low-pressure recirculation flow path 230, and the EGR gas amount flowing through the low-pressure recirculation flow path 230 is adjusted. On the other hand, the opening degree of the low-pressure EGR valve 62 may be controlled based only on the temperature of the EGR gas flowing through the low-pressure recirculation flow path 230, and the amount of EGR gas flowing through the low-pressure recirculation flow path 230 may be adjusted.

  In the above embodiment, one of the DPF 50 or the NOx catalyst 90 is installed in the exhaust passage 210 as an exhaust purification device. On the other hand, both the DPF 50 and the NOx catalyst 90 may be installed in the exhaust passage 210. Further, an oxidation catalyst may be installed on the exhaust upstream side of the DPF 50 or the NOx catalyst 90 in order to increase the exhaust temperature when an unburned component is added.

  In the above embodiment, the EGR gas amount is detected by subtracting the intake air amount before the EGR gas recirculates from the intake air amount flowing into the engine 2. On the other hand, a flow rate sensor may be installed in the low pressure recirculation channel 230 in order to detect the EGR gas amount.

  In the above embodiment, an example in which the present invention is applied to an exhaust gas purification system for a diesel engine has been described. On the other hand, if the exhaust gas is recirculated from the exhaust downstream side of the exhaust purification device to the intake side and the temperature of the exhaust downstream side of the exhaust purification device rises due to regeneration of the exhaust purification device, etc. The present invention can be applied to any exhaust gas purification system for an internal combustion engine such as an injection gasoline engine.

Further, the exhaust purification system of the present invention may be applied to an intake system that does not include the turbocharger 30.
In the above embodiment, at least some of the functions of the reflux temperature detection means, the reflux amount detection means, the reflux amount control means, and the temperature decrease amount estimation means are realized by the ECU 80 whose functions are specified by the control program. On the other hand, at least a part of the functions executed by the ECU 80 may be realized by hardware whose functions are specified by the circuit configuration itself.

  As described above, the present invention is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

10, 100, 110, 120, 130: Exhaust gas purification system, 14: Intake amount sensor (recirculation amount detection means), 22: Intake pressure sensor (recirculation temperature detection means, recirculation amount detection means), 24: Intake air temperature sensor (recirculation) Temperature detection means, recirculation amount detection means), 50: DPF (exhaust gas purification device), 52: Exhaust temperature sensor (recirculation temperature detection means), 54: Exhaust temperature sensor (downstream temperature sensor, recirculation temperature detection means), 60: Low pressure EGR cooler (exhaust cooling device), 62: low pressure EGR valve (recirculation amount adjustment valve), 64: exhaust temperature sensor (upstream temperature sensor, recirculation temperature detection means), 70: engine speed sensor (recirculation temperature detection means, recirculation amount) Detection means), 72: accelerator opening sensor (reflux temperature detection means), 80: ECU (reflux temperature detection means, reflux amount detection means, reflux amount control means, temperature drop amount estimation means), 90: Ox catalyst (exhaust gas purification device), 200: intake passage, 210: exhaust path, 230: low-pressure return channel (return channel)

Claims (18)

An exhaust purification device that is installed in an exhaust passage of an internal combustion engine to remove harmful components in the exhaust gas;
A recirculation amount adjusting valve for adjusting a recirculation amount of the exhaust gas recirculated from the exhaust side to the intake side, installed in a recirculation flow path for recirculating the exhaust gas on the exhaust downstream side of the exhaust purification device to the intake side;
A recirculation temperature detecting means for detecting a recirculation temperature of the exhaust gas recirculated from the exhaust side to the intake side through the recirculation flow path;
Recirculation amount control means for controlling the recirculation amount adjustment valve to adjust the recirculation amount based on the recirculation temperature detected by the recirculation temperature detection means;
Exhaust gas purification system, characterized in that it comprises a. A recirculation amount detecting means for detecting a recirculation amount of exhaust gas recirculated from the exhaust side to the intake side through the recirculation flow path;
The recirculation amount control means controls the recirculation amount adjustment valve to adjust the recirculation amount based on the recirculation temperature detected by the recirculation temperature detection means and the recirculation amount detected by the recirculation amount detection means;
An exhaust purifying system according to claim 1, characterized in that.   The recirculation amount detecting means estimates the recirculation amount based on an intake pressure and an intake air temperature in an intake manifold, a rotation speed of the internal combustion engine, and an intake air amount, and detects the recirculation amount as the recirculation amount. The exhaust purification system according to 2.   The recirculation amount control means controls the recirculation amount adjustment valve to reduce the recirculation amount as the recirculation amount detected by the recirculation amount detection means increases. Exhaust purification system.   The exhaust gas purification system according to any one of claims 1 to 4, wherein the recirculation temperature detection means detects the recirculation temperature based on an exhaust gas temperature downstream of the exhaust gas purification device. A filter for collecting particulates in the exhaust gas as the exhaust gas purification device;
The recirculation temperature detection means includes an exhaust gas temperature upstream of the exhaust gas purification device, an unburned component concentration upstream of the exhaust gas purification device, an oxygen concentration upstream of the exhaust gas purification device, and the exhaust gas. Of the amount of exhaust gas flowing into the purification device and the amount of particulates collected by the exhaust purification device, at least the exhaust gas temperature upstream of the exhaust purification device and the exhaust gas upstream of the exhaust purification device Based on the fuel component concentration and the amount of exhaust gas flowing into the exhaust purification device, the exhaust temperature downstream of the exhaust purification device is estimated, and the recirculation temperature is detected based on the estimated exhaust temperature.
The exhaust purification system according to claim 5. A filter for collecting particulates in the exhaust gas as the exhaust gas purification device;
The recirculation temperature detection means includes an exhaust gas temperature upstream of the exhaust gas purification device, an unburned component concentration upstream of the exhaust gas purification device, an oxygen concentration upstream of the exhaust gas purification device, and the exhaust gas. Of the exhaust gas amount flowing into the purification device and the particulate amount collected by the exhaust purification device, at least the exhaust gas temperature upstream of the exhaust purification device and the exhaust gas amount flowing into the exhaust purification device , Estimating the exhaust temperature on the exhaust downstream side of the exhaust purification device based on the particulate amount collected by the exhaust purification device, and detecting the recirculation temperature based on the estimated exhaust temperature,
An exhaust purifying system according to claim 5, characterized in that. A downstream temperature sensor installed on the exhaust downstream side of the exhaust purification device;
The recirculation temperature detection means detects the recirculation temperature based on the exhaust gas temperature on the exhaust downstream side of the exhaust gas purification device detected by the downstream temperature sensor.
An exhaust purifying system according to claim 5, characterized in that.   9. The recirculation amount control means controls the recirculation amount adjustment valve to reduce the recirculation amount as the recirculation temperature detected by the recirculation temperature detection means increases. The exhaust gas purification system according to claim 1.   The exhaust gas purification system according to any one of claims 1 to 9, further comprising an exhaust cooling device that is installed in the recirculation flow path and cools the exhaust gas recirculated from the exhaust side to the intake side.   The exhaust gas purification system according to claim 10, wherein the recirculation temperature detection means detects an exhaust gas temperature on the exhaust upstream side of the exhaust cooling device as the recirculation temperature. An exhaust cooling device that is installed in the return flow path and cools the exhaust gas recirculated from the exhaust side to the intake side;
The recirculation temperature detection means estimates the exhaust gas temperature on the exhaust upstream side of the exhaust cooling device based on the exhaust gas temperature on the exhaust gas downstream side of the exhaust gas purification device and the recirculation amount detected by the recirculation amount detection means. Detect as reflux temperature,
The exhaust gas purification system according to any one of claims 2 to 4, wherein A temperature decrease amount estimating means for estimating a temperature decrease amount of the exhaust temperature from the exhaust downstream side of the exhaust purification device to the exhaust upstream side of the exhaust cooling device;
The temperature decrease amount estimation means estimates that the temperature decrease amount decreases as the recirculation amount detected by the recirculation amount detection means increases, and the exhaust gas temperature on the exhaust downstream side of the exhaust purification device increases. the estimated as temperature drop amount increases in accordance with,
The recirculation temperature detection means subtracts the temperature decrease amount from the exhaust gas temperature on the exhaust gas downstream side of the exhaust gas purification device, calculates the exhaust gas temperature on the exhaust gas upstream side of the exhaust cooling device, and detects it as the recirculation temperature.
An exhaust purifying system according to claim 12, characterized in that.   The recirculation temperature detecting means further calculates an exhaust gas temperature upstream of the exhaust gas cooling device based on a time delay characteristic of the exhaust gas temperature from the exhaust gas downstream side of the exhaust gas purification device to the exhaust gas upstream side of the exhaust gas cooling device. The exhaust gas purification system according to claim 13, wherein the exhaust gas purification system is detected as the recirculation temperature. An exhaust cooling device that is installed in the return flow path and cools the exhaust gas recirculated from the exhaust side to the intake side;
An upstream temperature sensor that is installed on the exhaust upstream side of the exhaust cooling device and detects the exhaust temperature on the exhaust upstream side of the exhaust cooling device;
With
The recirculation temperature detection means detects the exhaust gas temperature on the exhaust upstream side of the exhaust cooling device detected by the upstream temperature sensor as the recirculation temperature.
The exhaust gas purification system according to any one of claims 1 to 4, wherein   16. The recirculation amount control means adjusts the recirculation amount by controlling the recirculation amount adjustment valve when the recirculation temperature detected by the recirculation temperature detection means is equal to or higher than a predetermined value. The exhaust gas purification system according to any one of the above.   The exhaust gas purification apparatus includes a filter that collects particulates in exhaust gas, and an oxidation catalyst is supported on the filter itself, or an oxidation catalyst installed on the exhaust gas upstream side of the filter. The exhaust gas purification system according to any one of claims 1 to 16.   The exhaust purification system according to any one of claims 1 to 17, further comprising an NOx storage reduction catalyst that removes NOx in the exhaust gas as the exhaust purification device.

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