JP4802992B2 - Exhaust gas recirculation device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine.

  A low-pressure EGR passage that takes a part of exhaust gas as low-pressure EGR gas from the exhaust passage downstream of the turbine of the turbocharger and returns the low-pressure EGR gas to an intake passage upstream of the compressor of the turbocharger, and an exhaust passage upstream of the turbine There is known an exhaust gas recirculation device for an internal combustion engine that includes a high pressure EGR passage that takes in a part of exhaust gas as high pressure EGR gas from the exhaust gas and recirculates the high pressure EGR gas to an intake passage downstream of the compressor.

And the technique provided with the low voltage | pressure EGR cooler which is arrange | positioned in the low voltage | pressure EGR channel | path and cools the low voltage | pressure EGR gas which flows through the inside of a low voltage | pressure EGR channel | path using engine cooling water is disclosed (refer patent document 1).
Japanese Patent Laying-Open No. 2005-076456 JP 2001-140701 A JP 11-193753 A

  By the way, at the time of low load or cold start, since the combustion temperature of the internal combustion engine is low and unburned HC is likely to be generated, a large amount of low pressure EGR gas (exhaust gas) cooled by the low pressure EGR cooler may be recirculated. Can not. For this reason, at the time of low load or cold start, the low pressure EGR valve is closed to restrict the exhaust gas recirculation. However, with the conventional configuration, if the low pressure EGR valve is closed, the exhaust gas does not flow to the low pressure EGR cooler. Therefore, the waste heat from the exhaust cannot be recovered in the engine cooling water by the low pressure EGR cooler. The warm-up of the internal combustion engine may be delayed due to the water not warming.

  An object of the present invention is to provide a technology for promoting warm-up of an internal combustion engine by recovering waste heat from the exhaust into the engine cooling water with a low-pressure EGR cooler and warming the engine cooling water in an exhaust gas recirculation device for an internal combustion engine. There is.

In the present invention, the following configuration is adopted. That is,
A turbocharger having a turbine disposed in an exhaust passage of the internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
An exhaust purification catalyst disposed in an exhaust passage downstream of the turbine;
A low pressure EGR passage that takes in a part of exhaust gas as a low pressure EGR gas from an exhaust passage downstream of the exhaust purification catalyst and recirculates the low pressure EGR gas to an intake passage upstream of the compressor;
A low pressure EGR valve that is disposed in the low pressure EGR passage and adjusts the amount of low pressure EGR gas;
A low-pressure EGR cooler that is disposed in a low-pressure EGR passage upstream of the low-pressure EGR valve and cools the low-pressure EGR gas using engine cooling water;
An exhaust throttle valve disposed in an exhaust passage downstream of a connection portion with the low pressure EGR passage;
An exhaust communication passage having one end connected to the low pressure EGR passage between the low pressure EGR cooler and the low pressure EGR valve, and the other end connected to an exhaust passage downstream of the exhaust throttle valve;
A first control means for controlling the exhaust throttle valve to a closed side and controlling the low-pressure EGR valve to a closed side when the engine cooling water is below a predetermined temperature;
An exhaust gas recirculation device for an internal combustion engine.

In the present invention, the following configuration is adopted. That is,
A turbocharger having a turbine disposed in an exhaust passage of the internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
An exhaust purification catalyst disposed in an exhaust passage downstream of the turbine;
A low pressure EGR passage that takes in a part of exhaust gas as a low pressure EGR gas from an exhaust passage downstream of the exhaust purification catalyst and recirculates the low pressure EGR gas to an intake passage upstream of the compressor;
A low pressure EGR valve that is disposed in the low pressure EGR passage and adjusts the amount of low pressure EGR gas;
A low-pressure EGR cooler that is disposed in a low-pressure EGR passage upstream of the low-pressure EGR valve and cools the low-pressure EGR gas using engine cooling water;
An exhaust throttle valve disposed in an exhaust passage downstream of a connection portion with the low pressure EGR passage;
An exhaust communication passage having one end connected to the low pressure EGR passage between the low pressure EGR cooler and the low pressure EGR valve, and the other end connected to an exhaust passage downstream of the exhaust throttle valve;
A high-pressure EGR passage that takes a part of exhaust gas as a high-pressure EGR gas from an exhaust passage upstream of the turbine and recirculates the high-pressure EGR gas to an intake passage downstream of the compressor;
A high pressure EGR valve that is disposed in the high pressure EGR passage and adjusts the amount of high pressure EGR gas;
Second control means for controlling the exhaust throttle valve to the closed side and controlling the high pressure EGR valve to the open side while controlling the low pressure EGR valve to the closed side when the engine cooling water is below a predetermined temperature; ,
An exhaust gas recirculation device for an internal combustion engine.

  As described above, the present invention includes an exhaust communication passage having one end connected to the low pressure EGR passage between the low pressure EGR cooler and the low pressure EGR valve and the other end connected to the exhaust passage downstream of the exhaust throttle valve. When the cooling water is below a predetermined temperature, the exhaust throttle valve is controlled to the closed side and the low pressure EGR valve is controlled to the closed side.

  Here, the predetermined temperature is a temperature at which it takes a long time to warm up the internal combustion engine when the engine cooling water has a low temperature below that and the engine cooling water is excessively low in temperature.

  According to this configuration, when the engine cooling water is below a predetermined temperature, the exhaust throttle valve is controlled to the closed side and the low pressure EGR valve is controlled to the closed side, so that the exhaust flowing through the exhaust passage is disposed in the low pressure EGR cooler. The exhaust that has flowed into the upstream side of the low-pressure EGR passage and has flowed through the low-pressure EGR cooler flows from the middle portion of the low-pressure EGR passage through the exhaust communication passage and is discharged again to the exhaust passage.

  Since the low pressure EGR cooler is provided in the middle of the low pressure EGR passage through which the exhaust flows when the exhaust flows through such a path, the waste heat from the exhaust can be recovered in the engine cooling water by the low pressure EGR cooler. Thereby, warming up of an internal combustion engine can be accelerated | stimulated by warming engine cooling water.

  Further, since the exhaust gas flowing through such a path flows into the low-pressure EGR passage from the exhaust passage downstream of the turbine, an amount of exhaust that can maintain sufficient supercharging passes through the turbine. For this reason, even when the above-described control is performed when the engine coolant is below a predetermined temperature, sufficient supercharging is maintained and fuel efficiency is not impaired.

Further, since the exhaust gas flowing in such a path flows from the exhaust passage downstream of the exhaust purification catalyst into the low pressure EGR passage, the exhaust warms the exhaust purification catalyst, and in addition, the exhaust has reaction heat of the catalyst in the exhaust purification catalyst. It will be. For this reason, the waste heat of the exhaust gas recovered by the low-pressure EGR cooler includes the reaction heat of the catalyst. Therefore, the amount of heat is increased and the engine cooling water can be further warmed to further promote the warm-up of the internal combustion engine. Further, since the exhaust gas passes through the exhaust gas purification catalyst and HC contained in the exhaust gas is removed by the exhaust gas purification catalyst, it is possible to suppress the exhaust gas flowing into the low pressure EGR cooler from contaminating the low pressure EGR cooler.

  Further, the present invention includes an exhaust communication passage having one end connected to the low pressure EGR passage between the low pressure EGR cooler and the low pressure EGR valve and the other end connected to the exhaust passage downstream of the exhaust throttle valve. When the water is below a predetermined temperature, the high-pressure EGR valve is controlled to open while the exhaust throttle valve is controlled to close and the low-pressure EGR valve is controlled to close.

  According to this configuration, the amount of low-pressure EGR gas is reduced by controlling the low-pressure EGR valve to the closed side, and the amount of high-pressure EGR gas is increased by controlling the high-pressure EGR valve to the open side to reduce the total amount of EGR gas. It can be secured. For this reason, even if it performs the said control, EGR driving | operation can be continued and the nitrogen oxide (NOx) reduction effect by performing EGR driving | operation can be acquired continuously.

  Moreover, since the exhaust gas as the high-pressure EGR gas is recirculated to the internal combustion engine as described above, the high-temperature high-pressure EGR gas contained in the intake air sucked into the internal combustion engine increases. As a result, the temperature of the intake air sucked into the internal combustion engine rises, and the temperature of the exhaust gas also rises. It is also possible to promote warming of the engine cooling water by the high-temperature exhaust gas flowing into the low-pressure EGR cooler.

  A shut-off valve that can shut off the exhaust communication path may be provided.

  According to this configuration, by shutting off the exhaust communication passage with the shut-off valve, the exhaust gas flows from the exhaust passage through the exhaust communication passage, flows into the low pressure EGR passage from the middle of the low pressure EGR passage, flows around the low pressure EGR cooler, and flows into the intake passage. I can prevent it. For this reason, it is possible to prevent the waste heat recovery efficiency of the low pressure EGR cooler from being lowered without bypassing the low pressure EGR cooler. Further, it is possible to prevent the exhaust gas bypassing the low pressure EGR cooler from flowing into the intake passage and increasing the temperature of the compressor.

In the present invention, the following configuration is adopted. That is,
A turbocharger having a turbine disposed in an exhaust passage of the internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
An exhaust purification catalyst disposed in an exhaust passage downstream of the turbine;
A low pressure EGR passage that takes in a part of exhaust gas as a low pressure EGR gas from an exhaust passage downstream of the exhaust purification catalyst and recirculates the low pressure EGR gas to an intake passage upstream of the compressor;
A low pressure EGR valve that is disposed in the low pressure EGR passage and adjusts the amount of low pressure EGR gas;
A low-pressure EGR cooler that is disposed in a low-pressure EGR passage upstream of the low-pressure EGR valve and cools the low-pressure EGR gas using engine cooling water;
An exhaust throttle valve disposed in an exhaust passage downstream of a connection portion with the low pressure EGR passage;
An exhaust communication passage having one end connected to the low pressure EGR passage between the low pressure EGR cooler and the low pressure EGR valve, and the other end connected to an exhaust passage downstream of the exhaust throttle valve;
A block that includes a portion of the low-pressure EGR passage where the low-pressure EGR cooler is disposed, and that can block the downstream side of the low-pressure EGR passage while communicating with the exhaust communication passage upstream and the connection portion with the exhaust communication passage. A valve,
A third control means for controlling the exhaust throttle valve to the closed side and shutting off the downstream side of the low-pressure EGR passage with the shut-off valve when the engine coolant is below a predetermined temperature;
An exhaust gas recirculation device for an internal combustion engine.

The present invention includes an exhaust communication passage having one end connected to the low pressure EGR passage between the low pressure EGR cooler and the low pressure EGR valve and the other end connected to the exhaust passage downstream of the exhaust throttle valve. When the temperature is lower than the predetermined temperature, the exhaust throttle valve is controlled to the closed side and the downstream side of the low pressure EGR passage is shut off by the shutoff valve.

  According to this configuration, when the engine cooling water is below a predetermined temperature, the exhaust throttle valve is controlled to the closed side and the downstream side of the low pressure EGR passage is shut off by the shutoff valve, so that the low pressure EGR valve is not operated. The exhaust gas flowing through the exhaust passage flows into the upstream side of the low pressure EGR passage where the low pressure EGR cooler is disposed, and the exhaust gas flowing through the low pressure EGR cooler flows from the middle portion of the low pressure EGR passage to the exhaust communication passage and is discharged again into the exhaust passage. Is done.

  When the operating state is high load and high rotation and the exhaust throttle valve is controlled to open, it is preferable to provide an exhaust communication path blocking means for blocking the exhaust communication path by the cutoff valve.

  According to this configuration, even if the exhaust throttle valve is opened to prevent pressure loss due to the operation state of high load and high rotation and the exhaust throttle valve is closed, the shutoff valve is used to connect the exhaust system. By shutting off the passage, it is possible to prevent exhaust from flowing from the exhaust passage to the exhaust communication passage and from the middle of the low pressure EGR passage into the low pressure EGR passage and bypassing the low pressure EGR cooler and flowing into the intake passage.

  Here, the shut-off valve is disposed at a connection portion between the low pressure EGR passage and the exhaust communication passage downstream of a portion where the low pressure EGR cooler is disposed, and connects the upstream side and the downstream side of the low pressure EGR passage. It is preferable that the exhaust communication passage can be shut off while communicating and the downstream side of the low pressure EGR passage can be shut off while communicating the upstream side of the low pressure EGR passage and the exhaust communication passage.

  When the temperature of the exhaust gas is lower than the temperature of the engine cooling water, an exhaust inflow prohibiting unit that prohibits the inflow of exhaust gas to the low pressure EGR cooler may be provided.

  According to this configuration, when the temperature of the exhaust gas is lower than the temperature of the engine cooling water, the inflow of the exhaust gas to the low pressure EGR cooler is prohibited, and the engine cooling water is cooled by the exhaust gas flowing into the low pressure EGR cooler. Can be prevented.

  According to the present invention, in the exhaust gas recirculation device for an internal combustion engine, waste heat from the exhaust can be recovered in the engine cooling water by the low pressure EGR cooler, and warming up of the internal combustion engine can be promoted by warming the engine cooling water.

  Specific examples of the present invention will be described below.

<Example 1>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the exhaust gas recirculation apparatus for an internal combustion engine according to this embodiment is applied and its intake / exhaust system.

  An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2 forming a combustion chamber. The internal combustion engine 1 is mounted on a vehicle. An intake passage 3 and an exhaust passage 4 are connected to the internal combustion engine 1.

In the middle of the intake passage 3 connected to the internal combustion engine 1, a compressor housing 5a of a turbocharger 5 that operates using exhaust energy as a drive source is disposed. A first throttle valve 6 for adjusting the flow rate of intake air flowing through the intake passage 3 is disposed in the intake passage 3 upstream of the compressor housing 5a. The first throttle valve 6 is opened and closed by an electric actuator. An air flow meter 7 that outputs a signal corresponding to the flow rate of the intake air (fresh air) flowing through the intake passage 3 is disposed in the intake passage 3 upstream of the first throttle valve 6. The air flow meter 7 measures the intake air amount (fresh air amount) of the internal combustion engine 1.

  An intercooler 8 that performs heat exchange between the intake air and the outside air is disposed in the intake passage 3 downstream of the compressor housing 5a. A second throttle valve 9 for adjusting the flow rate of the intake air flowing through the intake passage 3 is provided in the intake passage 3 downstream of the intercooler 8. The second throttle valve 9 is opened and closed by an electric actuator.

  On the other hand, a turbine housing 5 b of the turbocharger 5 is arranged in the middle of the exhaust passage 4 connected to the internal combustion engine 1. A particulate filter (hereinafter simply referred to as a filter) 10 is disposed in the exhaust passage 4 downstream of the turbine housing 5b. The filter 10 carries an NOx storage reduction catalyst (hereinafter simply referred to as NOx catalyst). The filter 10 collects particulate matter (PM) in the exhaust gas. Further, the NOx catalyst occludes NOx in the exhaust when the oxygen concentration of the exhaust flowing into the NOx catalyst is high, while the NOx that occluded when the oxygen concentration of the exhaust flowing into the NOx catalyst decreases. Release. At the time of the release, if a reducing component such as HC or carbon monoxide (CO) is present in the exhaust, NOx released from the NOx catalyst is reduced. Note that an oxidation catalyst or a three-way catalyst may be supported on the filter 10 instead of the NOx catalyst. The filter 10 carrying the NOx catalyst in this embodiment corresponds to the exhaust purification catalyst in the present invention.

  An exhaust throttle valve 11 that adjusts the flow rate of the exhaust gas flowing through the exhaust passage 4 is provided in the exhaust passage 4 downstream of the filter 10. The exhaust throttle valve 11 is opened and closed by an electric actuator.

  The internal combustion engine 1 is provided with a low pressure EGR device 30 that recirculates (recirculates) part of the exhaust gas flowing through the exhaust passage 4 to the intake passage 3 at a low pressure. 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 passage 4 downstream of the filter 10 and upstream of the exhaust throttle valve 11 and the intake passage 3 upstream of the compressor housing 5a and downstream of the first throttle valve 6. is doing. Exhaust gas is fed into the internal combustion engine 1 at low pressure through the low pressure EGR passage 31. In this embodiment, the exhaust gas recirculated through the low pressure EGR passage 31 is referred to as low pressure EGR gas.

  The low pressure EGR valve 32 adjusts the amount of the low pressure EGR gas flowing through the low pressure EGR passage 31 by adjusting the passage sectional area of the low pressure EGR passage 31.

  Further, the low-pressure EGR cooler 33 exchanges heat between the low-pressure EGR gas passing through the low-pressure EGR cooler 33 and the engine cooling water of the internal combustion engine 1 to reduce the temperature of the low-pressure EGR gas. Further, the low pressure EGR cooler 33 can also warm the engine cooling water by the low pressure EGR gas when the engine cooling water is at a lower temperature than the low pressure EGR gas.

  Here, the temperature of the engine cooling water can be detected by a cooling water temperature sensor 34 disposed in the flow path of the engine cooling water.

Further, in this embodiment, an exhaust communication system in which one end is connected to the low pressure EGR passage 31 between the low pressure EGR cooler 33 and the low pressure EGR valve 32 and the other end is connected to the exhaust passage 4 downstream of the exhaust throttle valve 11. A passage 50 is provided.

  On the other hand, the internal combustion engine 1 is provided with a high-pressure EGR device 40 that recirculates a part of the exhaust gas flowing through the exhaust passage 4 to the intake passage 3 at a high pressure. 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 passage 4 upstream of the turbine housing 5b and the intake passage 3 downstream of the compressor housing 5a. Exhaust gas is fed into the internal combustion engine 1 at a high pressure through the high pressure EGR passage 41. In this embodiment, the exhaust gas recirculated through the high pressure EGR passage 41 is referred to as high pressure EGR gas.

  Further, the high pressure EGR valve 42 adjusts the amount of high pressure EGR gas flowing through the high pressure EGR passage 41 by adjusting the passage sectional area of the high pressure EGR passage 41.

  The internal combustion engine 1 configured as described above is provided with an ECU 12 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 12 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  The ECU 12 includes an air flow meter 7, a coolant temperature sensor 34, an accelerator opening sensor 14 that can detect an engine load by outputting an electric signal corresponding to the amount of depression of the accelerator pedal 13 by the driver, and an engine rotational speed. The crank position sensor 15 is connected via electrical wiring, and the output signals of these various sensors are input to the ECU 12.

  On the other hand, the first throttle valve 6, the second throttle valve 9, the exhaust throttle valve 11, the low-pressure EGR valve 32, and the high-pressure EGR valve 42 are connected to the ECU 12 through electrical wiring. These devices are controlled.

  In this embodiment, the high-pressure EGR valve 42 is used to control the high-pressure EGR gas amount while the low-pressure EGR valve 32 is used to control the low-pressure EGR gas amount according to the operating state. As a result, a so-called EGR operation is performed in which the internal combustion engine 1 is operated in a state where the low-pressure EGR gas and the high-pressure EGR gas are contained in the intake air sucked into the internal combustion engine 1, and the oxygen concentration in the intake air is reduced to reduce the combustion temperature The effect of reducing NOx generated during combustion by reducing the speed is exhibited.

  By the way, at the time of low load or cold start, the combustion temperature of the internal combustion engine 1 is low and unburned HC is easily generated. Therefore, a large amount of low-pressure EGR gas (exhaust gas) cooled by the low-pressure EGR cooler 33 cannot be recirculated. For this reason, at the time of low load or cold start, the low pressure EGR valve 32 is closed to restrict the recirculation of the low pressure EGR gas (exhaust gas).

  However, it is desirable to promote warm-up of the internal combustion engine 1 by warming the engine coolant at a low load or cold start.

  Therefore, the present inventors collect waste heat of the exhaust and warm the engine cooling water by this heat so as not to waste the exhaust flowing through the exhaust passage 4 downstream from the turbine housing 5b that does not recirculate as the low-pressure EGR gas. I wondered if I could do it. In normal times, the low-pressure EGR cooler 33 that cools the low-pressure EGR gas by exchanging heat with the engine cooling water exchanges heat between the high-temperature exhaust and the low-temperature engine cooling water at the time of low load or cold start. And found that the engine cooling water can be warmed.

Here, if the low-pressure EGR gas is recirculated to the internal combustion engine 1 using the low-pressure EGR passage 31 in order to flow the exhaust gas to the low-pressure EGR cooler 33, the combustion temperature of the internal combustion engine 1 is low and unburned HC as described above. Therefore, the exhaust communication passage 50 is provided so that the exhaust gas flowing through the low pressure EGR cooler 33 flows from the low pressure EGR passage 31 to the exhaust passage 4 downstream of the connection portion of the low pressure EGR passage 31.

  Therefore, one end of the exhaust communication passage 50 is connected to the low pressure EGR passage 31 between the low pressure EGR cooler 33 and the low pressure EGR valve 32, and the other end is connected to the exhaust passage 4 downstream of the exhaust throttle valve 11. .

  Then, by controlling the exhaust throttle valve 11 to the closed side and the low pressure EGR valve 32 to be fully closed, the exhaust gas flowing through the exhaust passage 4 flows into the upstream side of the low pressure EGR passage 31 where the low pressure EGR cooler 33 is disposed. Then, it is found that an exhaust path for warming the engine coolant can be formed in which the exhaust gas flowing through the low pressure EGR cooler 33 flows from the middle portion of the low pressure EGR passage 31 through the exhaust communication passage 50 and is discharged to the exhaust passage 4 again. It was.

  Therefore, in this embodiment, the exhaust throttle valve 11 is controlled to the closed side at the time of low load or cold start, particularly when the engine cooling water that takes time to warm up the internal combustion engine 1 is equal to or lower than the temperature T1. At the same time, the low pressure EGR valve 32 is controlled to be fully closed.

  Here, the temperature T1 is a temperature at which the engine cooling water is excessively low in temperature when the engine cooling water is at a lower temperature, and it takes time to warm up the internal combustion engine 1.

  Therefore, according to this embodiment, when the engine cooling water is at a temperature T1 or less, the exhaust throttle valve 11 is controlled to the closed side and the low pressure EGR valve 32 is controlled to be fully closed, whereby the exhaust gas flowing through the exhaust passage 4 is controlled. Flows into the upstream side of the low pressure EGR passage 31 where the low pressure EGR cooler 33 is disposed, and the exhaust gas flowing through the low pressure EGR cooler 33 flows through the exhaust communication passage 50 from the middle portion of the low pressure EGR passage 31 and is discharged to the exhaust passage 4 again. Is done.

  Since the low-pressure EGR cooler 33 is provided in the middle of the low-pressure EGR passage 31 through which the exhaust flows when the exhaust flows through such a path, the waste heat from the exhaust can be recovered in the engine cooling water by the low-pressure EGR cooler 33. Thereby, warming up of the internal combustion engine 1 can be promoted by warming the engine coolant.

  Further, since the exhaust gas flowing through the above path when the engine coolant is at a temperature T1 or less flows from the exhaust passage 4 downstream of the turbine housing 5b into the low pressure EGR passage 31, an amount of exhaust capable of maintaining sufficient supercharging is generated in the turbine. It passes through the housing 5b. For this reason, even if the above-described control is performed when the engine cooling water is equal to or lower than the temperature T1, the internal combustion engine 1 maintains sufficient supercharging and does not impair fuel consumption.

  Further, since the exhaust gas flowing in this way flows from the exhaust passage 4 downstream of the filter 10 into the low pressure EGR passage 31, the exhaust heats the filter 10, and in addition, the exhaust has reaction heat of the catalyst in the filter 10. . For this reason, since the waste heat of the exhaust gas recovered by the low-pressure EGR cooler 33 includes the reaction heat of the catalyst, the amount of heat increases and the engine cooling water can be further warmed to further promote the warm-up of the internal combustion engine 1. . Further, since the exhaust gas passes through the filter 10 and HC contained in the exhaust gas is removed by the filter 10, it is possible to suppress the exhaust gas flowing into the low pressure EGR cooler 33 from contaminating the low pressure EGR cooler 33.

  Further, in this embodiment, when the engine coolant is at a temperature T1 or lower, the exhaust throttle valve 11 is controlled to be closed and the low pressure EGR valve 32 is controlled to be fully closed, while the high pressure EGR valve 42 is set to the open side. Control.

  According to this configuration, the amount of low-pressure EGR gas is reduced by controlling the low-pressure EGR valve 32 to be fully closed, and the amount of high-pressure EGR gas is increased by controlling the high-pressure EGR valve 42 to the open side. The amount can be secured. For this reason, the EGR operation can be continued, and the NOx reduction effect by performing the EGR operation can be continuously obtained.

  Further, since the exhaust gas as the high pressure EGR gas is recirculated more to the internal combustion engine 1 as described above, the high temperature high pressure EGR gas contained in the intake air taken into the internal combustion engine 1 increases. As a result, the temperature of the intake air taken into the internal combustion engine 1 rises, and the temperature of the exhaust gas also rises. It is also possible to promote warming of the engine cooling water by the high-temperature exhaust gas flowing into the low-pressure EGR cooler 33.

  Next, a control flow of the exhaust throttle valve 11, the low pressure EGR valve 32, and the high pressure EGR valve 42 according to the engine cooling water temperature according to this embodiment will be described. FIG. 2 is a flowchart showing a routine for controlling the exhaust throttle valve 11, the low pressure EGR valve 32, and the high pressure EGR valve 42 according to the temperature of the engine cooling water according to this embodiment. This routine is repeatedly executed every predetermined time. The ECU 12 that executes this routine corresponds to the first and second control means of the present invention.

  In step S101, the ECU 12 detects the engine coolant temperature THW using the coolant temperature sensor 34.

  In step S102 that moves from step S101, the ECU 12 determines whether or not the temperature THW of the engine cooling water is equal to or lower than the temperature T1 (THW ≦ T1?).

  Here, the temperature T1 is a temperature at which the engine cooling water is excessively low when the engine cooling water is at a lower temperature, and it takes time to warm up the internal combustion engine 1, and is determined in advance by experiments or the like. Temperature.

  If a negative determination is made in step S102, the ECU 12 proceeds to step S105. If an affirmative determination is made, the process proceeds to step S103.

  In step S103, the ECU 12 controls the low pressure EGR valve 32 to be fully closed and controls the high pressure EGR valve 42 to the open side.

  Here, the amount of opening increase to the opening side of the high pressure EGR valve 42 is the amount of opening increase that can increase the amount of high pressure EGR gas that compensates for the amount of low pressure EGR gas that decreases when the low pressure EGR valve 32 is fully closed. It is.

  By controlling the low pressure EGR valve 32 to be fully closed, the recirculation of the low pressure EGR gas is stopped when the temperature THW of the engine cooling water is equal to or lower than the temperature T1. Further, by controlling the high-pressure EGR valve 42 to the open side, the high-pressure EGR gas amount is increased and the total EGR gas amount can be ensured by the amount that the low-pressure EGR valve 32 is fully closed and the low-pressure EGR gas amount is reduced.

  In step S104, which shifts from step S103, the ECU 12 adjusts the opening of the exhaust throttle valve 11 using a subroutine.

  The subroutine is a routine for selecting a map for adjusting the opening of the exhaust throttle valve 11 depending on whether or not the low pressure EGR valve 32 is fully closed, and adjusting the opening of the exhaust throttle valve 11 according to the map.

In this subroutine, as shown in FIG. 3, the engine speed Ne is calculated from the output value of the crank position sensor 15, and the fuel injection amount Q injected into the cylinder 2 of the internal combustion engine 1 is calculated (step S201). It is determined whether or not the low pressure EGR valve 32 is fully closed (step S202). If the low pressure EGR valve 32 is fully closed, the opening degree of the exhaust throttle valve 11 is adjusted according to the map g (Ne, Q) (step S203). If the low pressure EGR valve 32 is not fully closed, the opening degree of the exhaust throttle valve 11 is adjusted by the map f (N, Q) (step S204).

  The map g (Ne, Q) and the map f (N, Q) are three-dimensional maps of the opening degree of the exhaust throttle valve 11, the engine speed Ne, and the fuel injection amount Q, and are obtained in advance through experiments or the like. The opening of the exhaust throttle valve 11 can be obtained by substituting the engine speed Ne and the fuel injection amount Q into the map g (Ne, Q) and the map f (N, Q). . Further, when the map g (Ne, Q) and the map f (N, Q) are compared, if the engine speed Ne and the fuel injection amount Q are substantially equal, the map g (Ne, Q) is the exhaust throttle valve. The value which controls 11 to the close side is taken.

  Returning to the description of step S104, the subroutine is executed, and the low-pressure EGR valve 32 is fully closed in step S103. Therefore, the opening degree of the exhaust throttle valve 11 is adjusted by the map g (Ne, Q).

  Thereby, when the opening degree of the exhaust throttle valve 11 is adjusted to the closed side by the map g (Ne, Q), the exhaust gas flowing through the exhaust passage 4 flows into the upstream side of the low pressure EGR passage 31 where the low pressure EGR cooler 33 is arranged. The exhaust gas that has flowed through the low-pressure EGR cooler 33 flows from the middle portion of the low-pressure EGR passage 31 through the exhaust communication passage 50 and is discharged to the exhaust passage 4 again.

  Since the low-pressure EGR cooler 33 is provided in the middle of the low-pressure EGR passage 31 through which the exhaust flows when the exhaust flows through the above-described path, the low-pressure EGR cooler 33 converts the waste heat from the exhaust into the engine cooling water. Can be recovered. Thereby, warming up of the internal combustion engine 1 can be promoted by warming the engine coolant.

  On the other hand, in step S105, the ECU 12 determines whether the temperature THW of the engine coolant is equal to or lower than the temperature T2 (THW ≦ T2?).

  Here, if the temperature T2 is higher than the temperature T1 (T1 <T2) and the engine cooling water is lower than the temperature T1, the engine cooling water is still lower than usual and the internal combustion engine is being operated while performing the EGR operation. 1 is a temperature at which the warming-up of 1 is desired to be further promoted, and is a temperature determined in advance by experiments or the like.

  If a negative determination is made in step S105, the ECU 12 proceeds to step S108. If an affirmative determination is made, the process proceeds to step S106.

  In step S106, the ECU 12 controls the low pressure EGR valve 32 to an open state that is not at least fully closed. At this time, the high-pressure EGR valve 42 is appropriately controlled according to the required amount of EGR gas.

  By controlling the low pressure EGR valve 32 to at least an open state that is not fully closed, the low pressure EGR gas is recirculated when the engine cooling water temperature THW is equal to or lower than the temperature T2.

  In step S107, which is shifted from step S106, the ECU 12 adjusts the opening degree of the exhaust throttle valve 11 using a subroutine.

In this step, the subroutine shown in FIG. 3 is executed, and since the low pressure EGR valve is not fully closed in step S105, the opening degree of the exhaust throttle valve 11 is adjusted by the map f (Ne, Q).

  By controlling the opening degree of the exhaust throttle valve 11 to be not fully opened, the exhaust water easily flows into the low-pressure EGR passage 31 when the temperature THW of the engine cooling water is equal to or lower than the temperature T2, and the low-pressure EGR cooler. The flow rate of the exhaust gas flowing through the exhaust gas 33 is made larger than when the exhaust throttle valve 11 is fully open. A part of the exhaust gas flowing into the low-pressure EGR cooler 33 returns to the internal combustion engine 1 through the downstream side of the low-pressure EGR passage 31 and the other part is discharged to the exhaust passage 4 through the exhaust communication passage 50. .

  Therefore, when the engine cooling water temperature THW is equal to or lower than the temperature T2, since the low pressure EGR valve 32 is open, the EGR operation is performed using the low pressure EGR gas, and the flow rate of the exhaust gas flowing through the low pressure EGR cooler 33 is Since there are more throttle valves 11 than when the throttle valve 11 is fully open, the warm-up of the internal combustion engine 1 is further promoted.

  In step S108, since the engine coolant is warmed, the ECU 12 fully opens the opening of the exhaust throttle valve 11, and the internal combustion engine 1 performs normal EGR operation.

  As described above, the exhaust communication passage 50 is provided, and the exhaust throttle valve 11, the low-pressure EGR valve 32, and the high-pressure EGR valve 42 are controlled according to the temperature of the engine cooling water. Heat can be recovered in the engine cooling water, and warming up of the internal combustion engine 1 can be promoted by warming the engine cooling water.

<Example 2>
Next, Example 2 will be described. In the following, description of the same points as in the above embodiment will be omitted, and only different points will be described.

  When the temperature of the engine cooling water is higher than the temperature of the exhaust gas discharged from the filter 10, when the exhaust gas flows into the low pressure EGR cooler 33, the engine cooling water is cooled instead. Therefore, in this embodiment, when the exhaust gas temperature Tc is lower than the engine coolant temperature THW, the inflow of exhaust gas to the low pressure EGR cooler 33 is prohibited.

  Here, the exhaust temperature is obtained from the output value of the exhaust temperature sensor 16 disposed in the exhaust passage 4 immediately downstream of the filter 10 shown in FIG. And the method of prohibiting the exhaust_gas | exhaustion which flows in into the low voltage | pressure EGR cooler 33 is controlling the low pressure EGR valve 32 fully closed and controlling the exhaust throttle valve 11 fully opened.

  Therefore, according to this embodiment, when the temperature of the exhaust gas is lower than the temperature of the engine cooling water, the inflow of the exhaust gas to the low pressure EGR cooler 33 is prohibited and the exhaust gas flowing into the low pressure EGR cooler 33 causes the engine cooling water to flow. On the contrary, it can be prevented from being cooled.

  Next, a control flow of the exhaust throttle valve 11, the low pressure EGR valve 32, and the high pressure EGR valve 42 according to the engine cooling water temperature according to this embodiment will be described. FIG. 4 is a flowchart showing a routine for controlling the exhaust throttle valve 11, the low pressure EGR valve 32, and the high pressure EGR valve 42 according to the temperature of the engine cooling water according to this embodiment. This routine is repeatedly executed every predetermined time. The ECU 12 that executes this routine corresponds to the exhaust inflow prohibiting means of the present invention.

  Here, steps S101 to S108 in the flow shown in FIG. 4 are the same as those in the first embodiment.

In step S101, the ECU 12 detects the engine coolant temperature THW using the coolant temperature sensor 34.

  In step S301, which proceeds from step S101, the ECU 12 uses the exhaust temperature sensor 16 to detect the temperature Tc of the exhaust discharged from the filter 10.

  In step S302, which is shifted from step S301, the ECU 12 determines whether or not the engine cooling water temperature THW is equal to or lower than the exhaust gas temperature Tc (THW ≦ Tc?).

  If a negative determination is made in step S302, the ECU 12 proceeds to step S303. If a positive determination is made, the process proceeds to step S102.

  In step S303, the ECU 12 controls the low pressure EGR valve 32 to be fully closed and controls the exhaust throttle valve 11 to be fully open.

  As described above, when the exhaust gas temperature Tc is lower than the engine cooling water temperature THW, the exhaust gas flowing into the low pressure EGR cooler 33 is prevented from flowing into the low pressure EGR cooler 33 so that the engine cooling water is On the contrary, it can be prevented from being cooled.

<Example 3>
Next, Example 3 will be described. In the following, description of the same points as in the above embodiment will be omitted, and only different points will be described.

  In some cases, exhaust gas flows from the exhaust passage 4 through the exhaust communication passage 50 and flows into the low pressure EGR passage 31 from the middle of the low pressure EGR passage 31 and flows into the intake passage 3 bypassing the low pressure EGR cooler 33. Therefore, in this embodiment, as shown in FIG. 5, a shutoff valve 51 capable of shutting off the exhaust communication passage 50 is provided.

  The shut-off valve 51 is disposed at a connection portion between the low pressure EGR passage 31 and the exhaust communication passage 50 and is connected to the exhaust communication passage 50 where the low pressure EGR cooler 33 of the low pressure EGR passage 31 is disposed by being controlled by the ECU 12. The exhaust communication passage 50 can be blocked while communicating between the upstream side of the portion and the downstream side of the connection portion of the low pressure EGR passage 31 to the exhaust communication passage 50 where the low pressure EGR valve 32 is disposed. At the same time, the downstream side of the low pressure EGR passage 31 can be blocked while the upstream side of the low pressure EGR passage 31 and the exhaust communication passage 50 are communicated. Note that the arrangement of the shutoff valve 51 is not limited to the present embodiment as long as the above-described flow path can be formed. For example, the shutoff valve 51 is located downstream of the low-pressure EGR passage 31 from the exhaust communication passage 50 and upstream of the low-pressure EGR valve 32. It may be arranged.

  The shut-off valve 51 shuts off the downstream side of the low-pressure EGR passage 31, so that the exhaust passage 4 returns to the exhaust passage 4 from the exhaust passage 4 to the upstream side of the low-pressure EGR passage 31, via the exhaust communication passage 50, regardless of the operation of the low-pressure EGR valve 32. A return path can be formed.

  Further, when the shut-off valve 51 shuts off the exhaust communication passage 50, the exhaust gas flows from the exhaust passage 4 through the exhaust communication passage 50 and flows into the low-pressure EGR passage 31 from the middle of the low-pressure EGR passage 31, bypassing the low-pressure EGR cooler 33 and taking in the air. Inflow to the passage 3 can be prevented. For this reason, it is possible to prevent the waste heat recovery efficiency of the low pressure EGR cooler 33 from being lowered without bypassing the low pressure EGR cooler 33. In addition, it is possible to prevent the exhaust that bypasses the low pressure EGR cooler 33 from flowing into the intake passage 3 and the temperature of the compressor housing 5a from rising.

Next, a control flow of the exhaust throttle valve 11, the low pressure EGR valve 32, the high pressure EGR valve 42, and the shutoff valve 51 according to the temperature of the engine cooling water according to this embodiment will be described. FIG. 6 is a flowchart showing a routine for controlling the exhaust throttle valve 11, the low pressure EGR valve 32, the high pressure EGR valve 42, and the shutoff valve 51 according to the engine coolant temperature according to this embodiment. This routine is repeatedly executed every predetermined time. The ECU 12 that executes this routine corresponds to the first and second control means of the present invention.

  Here, steps S101 to S107 in the flow shown in FIG. 6 are the same as those in the first embodiment.

  If a negative determination is made in step S102, the ECU 12 proceeds to step S105. If a positive determination is made, the process proceeds to step S401.

  In step S401, the ECU 12 controls the low-pressure EGR valve 32 to be fully closed, controls the high-pressure EGR valve 42 to the open side, and shuts off the downstream side of the low-pressure EGR passage 31 with the shut-off valve 51. And the exhaust communication passage 50 communicate with each other.

  In step S104, which is shifted from step S401, the ECU 12 adjusts the opening degree of the exhaust throttle valve 11 using a subroutine.

  On the other hand, if a negative determination is made in step S105, the ECU 12 proceeds to step S403. If a positive determination is made, the process proceeds to step S402.

  In step S402, the ECU 12 controls the low pressure EGR valve 32 to an open state that is not at least fully closed. Further, the shutoff valve 51 blocks the exhaust communication passage 50 so that the upstream side of the low pressure EGR passage 31 communicates with the downstream side of the low pressure EGR passage 31. At this time, the high-pressure EGR valve 42 is appropriately controlled according to the required amount of EGR gas.

  As a result, the exhaust gas flowing through the exhaust passage 4 flows into the upstream side of the low-pressure EGR passage 31 where the low-pressure EGR cooler 33 is disposed, and the exhaust gas flowing through the low-pressure EGR cooler 33 flows downstream of the low-pressure EGR passage 31. 3 is discharged.

  Further, by shutting off the exhaust communication passage 50 with the shut-off valve 51, the exhaust gas flows from the exhaust passage 4 through the exhaust communication passage 50 and flows into the low pressure EGR passage 31 from the middle of the low pressure EGR passage 31, bypassing the low pressure EGR cooler 33 and taking in the air. Inflow to the passage 3 can be prevented.

  In step S107, which shifts from step S402, the ECU 12 adjusts the opening of the exhaust throttle valve 11 using a subroutine.

  On the other hand, in step S403, since the engine coolant is warmed, the ECU 12 fully opens the opening of the exhaust throttle valve 11, shuts off the exhaust communication passage 50 with the shutoff valve 51, and upstream of the low pressure EGR passage 31. And the downstream side of the low pressure EGR passage 31 communicate with each other, and the internal combustion engine 1 performs normal EGR operation.

  Also in this step, by shutting off the exhaust communication passage 50 with the shut-off valve 51, the exhaust gas flows from the exhaust passage 4 through the exhaust communication passage 50 to the low pressure EGR passage 31 from the middle of the low pressure EGR passage 31, and bypasses the low pressure EGR cooler 33. Thus, it is possible to prevent the air from flowing into the intake passage 3.

  As described above, the low-pressure EGR cooler 33 includes the exhaust communication passage 50 and controls the exhaust throttle valve 11, the low-pressure EGR valve 32, the high-pressure EGR valve 42, and the shut-off valve 51 according to the temperature of the engine coolant. Waste heat from the exhaust can be recovered in the engine cooling water, and warming up of the internal combustion engine 1 can be promoted by warming the engine cooling water.

<Example 4>
Next, Example 4 will be described. In the following, description of the same points as in the above embodiment will be omitted, and only different points will be described.

  When the temperature of the engine cooling water is higher than the temperature of the exhaust gas discharged from the filter 10, when the exhaust gas flows into the low pressure EGR cooler 33, the engine cooling water is cooled instead. Therefore, in this embodiment, when the exhaust gas temperature Tc is lower than the engine coolant temperature THW, the inflow of exhaust gas to the low pressure EGR cooler 33 is prohibited.

  Here, the exhaust temperature is obtained from the output value of the exhaust temperature sensor 16 arranged in the exhaust passage 4 immediately downstream of the filter 10 shown in FIG. The method for prohibiting the exhaust gas flowing into the low pressure EGR cooler 33 is to control the exhaust throttle valve 11 to be fully open, control the low pressure EGR valve 32 to be fully closed, and shut off the exhaust communication passage 50 with the shut-off valve 51. is there.

  Therefore, according to this embodiment, when the temperature of the exhaust gas is lower than the temperature of the engine cooling water, the inflow of the exhaust gas to the low pressure EGR cooler 33 is prohibited and the exhaust gas flowing into the low pressure EGR cooler 33 causes the engine cooling water to flow. On the contrary, it can be prevented from being cooled.

  Next, a control flow of the exhaust throttle valve 11, the low pressure EGR valve 32, the high pressure EGR valve 42, and the shutoff valve 51 according to the temperature of the engine cooling water according to this embodiment will be described. FIG. 7 is a flowchart showing a routine for controlling the exhaust throttle valve 11, the low pressure EGR valve 32, the high pressure EGR valve 42, and the shutoff valve 51 according to the engine coolant temperature according to this embodiment. This routine is repeatedly executed every predetermined time. The ECU 12 that executes this routine corresponds to the exhaust inflow prohibiting means of the present invention.

  Here, steps S101 to S107 and S401 to S403 in the flow shown in FIG. 7 are the same as those in the third embodiment.

  In step S101, the ECU 12 detects the engine coolant temperature THW using the coolant temperature sensor 34.

  In step S501, which is shifted from step S101, the ECU 12 uses the exhaust temperature sensor 16 to detect the temperature Tc of the exhaust discharged from the filter 10.

  In step S502, which proceeds from step S501, the ECU 12 determines whether or not the engine cooling water temperature THW is equal to or lower than the exhaust gas temperature Tc (THW ≦ Tc?).

  If a negative determination is made in step S502, the ECU 12 proceeds to step S503. If a positive determination is made, the process proceeds to step S102.

  In step S <b> 503, the ECU 12 controls the low pressure EGR valve 32 to be fully closed, controls the exhaust throttle valve 11 to be fully open, and shuts off the exhaust communication passage 50 with the shutoff valve 51.

  As described above, when the exhaust gas temperature Tc is lower than the engine cooling water temperature THW, the exhaust gas flowing into the low pressure EGR cooler 33 is prevented from flowing into the low pressure EGR cooler 33 so that the engine cooling water is On the contrary, it can be prevented from being cooled.

<Example 5>
Next, Example 5 will be described. In the following, description of the same points as in the above embodiment will be omitted, and only different points will be described.

  In this embodiment, only the exhaust throttle valve 11 and the shutoff valve 51 are controlled, and the low pressure EGR valve 32 is only subjected to normal control for performing EGR operation, and is not forcibly controlled.

  Therefore, the exhaust gas flowing through the exhaust passage 4 flows into the upstream side of the low-pressure EGR passage 31 where the low-pressure EGR cooler 33 is disposed, and the exhaust gas flowing through the low-pressure EGR cooler 33 passes from the middle of the low-pressure EGR passage 31 to the exhaust communication passage 50. The shutoff valve 51 communicates between the upstream side of the low pressure EGR passage 31 and the exhaust communication passage 50 so as to form an exhaust passage for warming the engine coolant that is discharged to the exhaust passage 4 again. The downstream side of the EGR passage 31 is blocked. The basic configuration of the internal combustion engine 1 including the shutoff valve 51 in the present embodiment is the same as that in the third embodiment shown in FIG.

  Therefore, according to the present embodiment, when the engine cooling water is equal to or lower than the temperature T1, the exhaust throttle valve 11 is controlled to the closed side, and the downstream side of the low pressure EGR passage 31 is shut off by the shutoff valve 51, whereby the exhaust passage 4 flows into the upstream side of the low-pressure EGR passage 31 where the low-pressure EGR cooler 33 is disposed, and the exhaust gas flowing through the low-pressure EGR cooler 33 flows through the exhaust communication passage 50 from the middle of the low-pressure EGR passage 31 to exhaust again. It is discharged to the passage 4.

  Since the low-pressure EGR cooler 33 is provided in the middle of the low-pressure EGR passage 31 through which the exhaust flows when the exhaust flows through such a path, the waste heat from the exhaust can be recovered in the engine cooling water by the low-pressure EGR cooler 33. Thereby, warming up of the internal combustion engine 1 can be promoted by warming the engine coolant.

  Further, when the operation state is high load and high rotation, the exhaust throttle valve 11 is opened to prevent pressure loss due to the exhaust throttle valve 11 being closed. However, when the exhaust throttle valve 11 is opened, the low-pressure EGR valve 32 may be opened in this embodiment, so that the exhaust flows from the exhaust passage 4 through the exhaust communication passage 50 and the low-pressure EGR passage 31. In some cases, the air flows into the low pressure EGR passage 31 from the middle and flows into the intake passage 3 bypassing the low pressure EGR cooler 33. Therefore, in this embodiment, when the operating state is high load and high rotation, and the opening degree ETHV of the exhaust throttle valve 11 is larger than the opening degree L1, the shutoff valve 51 is located upstream and downstream of the low pressure EGR passage 31. The exhaust communication passage 50 is blocked while communicating with the side.

  Therefore, by shutting off the exhaust communication passage 50 with the shut-off valve 51, the exhaust gas flows from the exhaust passage 4 through the exhaust communication passage 50 and flows into the low pressure EGR passage 31 from the middle of the low pressure EGR passage 31, bypassing the low pressure EGR cooler 33 and taking in the air. Inflow to the passage 3 can be prevented. For this reason, it is possible to prevent the waste heat recovery efficiency of the low pressure EGR cooler 33 from being lowered without bypassing the low pressure EGR cooler 33. In addition, it is possible to prevent the exhaust that bypasses the low pressure EGR cooler 33 from flowing into the intake passage 3 and the temperature of the compressor housing 5a from rising.

  Next, the control flow of the exhaust throttle valve 11 and the shutoff valve 51 according to the temperature of the engine cooling water according to this embodiment will be described. FIG. 8 is a flowchart showing a routine for controlling the exhaust throttle valve 11 and the shutoff valve 51 according to the temperature of the engine cooling water according to this embodiment. This routine is repeatedly executed every predetermined time. The ECU 12 that executes this routine corresponds to the third control means and the exhaust communication path blocking means of the present invention.

  In step S601, the ECU 12 detects the engine coolant temperature THW using the coolant temperature sensor 34.

  In step S602, which proceeds from step S601, the ECU 12 determines whether or not the temperature THW of the engine cooling water is equal to or lower than the temperature T1 (THW ≦ T1?).

  If a negative determination is made in step S602, the ECU 12 proceeds to step S608. If a positive determination is made, the process proceeds to step S603.

  In step S <b> 603, the ECU 12 calculates the engine speed Ne from the output value of the crank position sensor 15 and calculates the fuel injection amount Q injected into the cylinder 2 of the internal combustion engine 1.

  In step S604, which proceeds from step S603, the ECU 12 adjusts the opening degree ETHV of the exhaust throttle valve 11 by using the map h (Ne, Q).

  The map h (Ne, Q) is a three-dimensional map of the opening degree of the exhaust throttle valve 11, the engine speed Ne, and the fuel injection amount Q, and is obtained in advance through experiments or the like, and the map h ( The opening degree ETHV of the exhaust throttle valve 11 can be obtained by substituting the engine speed Ne and the fuel injection amount Q into Ne, Q). The map h (Ne, Q) estimates the operating state from the engine speed Ne and the fuel injection amount Q, and adjusts the opening of the exhaust throttle valve 11 according to the operating state. For this reason, when the operating state becomes a high load and a high rotation, the opening degree ETHV of the exhaust throttle valve 11 becomes small (open side).

  In step S605, which proceeds from step S604, the ECU 12 determines whether or not the opening degree ETHV of the exhaust throttle valve 11 obtained in step S604 is smaller (open side) than the opening degree L1 (ETHV <L1?). .

  Here, when the opening degree of the exhaust throttle valve 11 is smaller (open side) than the opening degree L1, the exhaust throttle valve 11 is made larger in order to prevent pressure loss in a high load and high rotation operation state. This is the opening degree that is opened, and is an opening degree that is determined in advance through experiments or the like.

  If a negative determination is made in step S605 (the closing side is greater than the opening degree L1), the ECU 12 proceeds to step S606. On the other hand, if an affirmative determination is made (opener side than the opening degree L1), the process proceeds to step S607.

  In step S <b> 606, the ECU 12 blocks the downstream side of the low-pressure EGR passage 31 with the shut-off valve 51 to connect the upstream side of the low-pressure EGR passage 31 and the exhaust communication passage 50.

  As a result, the exhaust gas flowing through the exhaust passage 4 flows into the upstream side of the low pressure EGR passage 31 where the low pressure EGR cooler 33 is disposed, and the exhaust gas flowing through the low pressure EGR cooler 33 passes from the middle of the low pressure EGR passage 31 to the exhaust communication passage 50. And is discharged to the exhaust passage 4 again.

  On the other hand, in step S607, the ECU 12 determines that the operation state is high load and high rotation, and shuts off the exhaust communication passage 50 with the shut-off valve 51 to connect the upstream side and the downstream side of the low pressure EGR passage 31.

  As a result, the exhaust gas flowing through the exhaust passage 4 flows into the upstream side of the low-pressure EGR passage 31 where the low-pressure EGR cooler 33 is disposed, and the exhaust gas flowing through the low-pressure EGR cooler 33 flows downstream of the low-pressure EGR passage 31. 3 is discharged.

  Further, by shutting off the exhaust communication passage 50 with the shut-off valve 51, the exhaust gas flows from the exhaust passage 4 through the exhaust communication passage 50 and flows into the low pressure EGR passage 31 from the middle of the low pressure EGR passage 31, bypassing the low pressure EGR cooler 33 and taking in the air. Inflow to the passage 3 can be prevented.

On the other hand, in step S608, since the engine coolant is warmed, the ECU 12 fully opens the opening of the exhaust throttle valve 11, shuts off the exhaust communication passage 50 with the shutoff valve 51, and upstream of the low pressure EGR passage 31. And the downstream side of the low pressure EGR passage 31 communicate with each other, and the internal combustion engine 1 performs normal EGR operation.

  Also in this step, by shutting off the exhaust communication passage 50 with the shut-off valve 51, the exhaust gas flows from the exhaust passage 4 through the exhaust communication passage 50 to the low pressure EGR passage 31 from the middle of the low pressure EGR passage 31, and bypasses the low pressure EGR cooler 33. Thus, it is possible to prevent the air from flowing into the intake passage 3.

  As described above, the exhaust communication passage 50 is provided, and the exhaust throttle valve 11 and the shutoff valve 51 are controlled according to the temperature of the engine cooling water, whereby the waste heat from the exhaust gas is converted into the engine cooling water by the low pressure EGR cooler 33. The engine cooling water can be warmed up and the warm-up of the internal combustion engine 1 can be promoted.

  The exhaust gas recirculation apparatus for an internal combustion engine according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention.

1 is a diagram illustrating an internal combustion engine and an intake / exhaust system thereof according to Embodiment 1. FIG. 3 is a flowchart showing a routine for controlling an exhaust throttle valve, a low pressure EGR valve, and a high pressure EGR valve according to the temperature of engine cooling water according to the first embodiment. 6 is a flowchart illustrating a subroutine for adjusting the opening of the exhaust throttle valve according to the first embodiment. 7 is a flowchart illustrating a routine for controlling an exhaust throttle valve, a low pressure EGR valve, and a high pressure EGR valve according to the temperature of engine cooling water according to a second embodiment. FIG. 6 is a diagram illustrating an internal combustion engine and an intake / exhaust system thereof according to a third embodiment. 12 is a flowchart showing a routine for controlling an exhaust throttle valve, a low pressure EGR valve, a high pressure EGR valve, and a shutoff valve according to the temperature of engine cooling water according to a third embodiment. 10 is a flowchart showing a routine for controlling an exhaust throttle valve, a low pressure EGR valve, a high pressure EGR valve, and a shutoff valve according to the temperature of engine cooling water according to a fourth embodiment. 10 is a flowchart showing a routine for controlling an exhaust throttle valve and a shutoff valve according to the temperature of engine cooling water according to a fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Intake passage 4 Exhaust passage 5 Turbocharger 5a Compressor housing 5b Turbine housing 6 Throttle valve 7 Air flow meter 8 Intercooler 9 Throttle valve 10 Filter 11 Exhaust throttle valve 12 ECU
13 Accelerator pedal 14 Accelerator opening sensor 15 Crank position sensor 16 Exhaust temperature sensor 30 Low pressure EGR device 31 Low pressure EGR passage 32 Low pressure EGR valve 33 Low pressure EGR cooler 34 Cooling water temperature sensor 40 High pressure EGR device 41 High pressure EGR passage 42 High pressure EGR valve 50 Exhaust communication passage 51 Shut-off valve

Claims (5)

A turbocharger having a turbine disposed in an exhaust passage of the internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
An exhaust purification catalyst disposed in an exhaust passage downstream of the turbine;
A low pressure EGR passage that takes in a part of exhaust gas as a low pressure EGR gas from an exhaust passage downstream of the exhaust purification catalyst and recirculates the low pressure EGR gas to an intake passage upstream of the compressor;
A low pressure EGR valve that is disposed in the low pressure EGR passage and adjusts the amount of low pressure EGR gas;
A low-pressure EGR cooler that is disposed in a low-pressure EGR passage upstream of the low-pressure EGR valve and cools the low-pressure EGR gas using engine cooling water;
An exhaust throttle valve disposed in an exhaust passage downstream of a connection portion with the low pressure EGR passage;
An exhaust communication passage having one end connected to the low pressure EGR passage between the low pressure EGR cooler and the low pressure EGR valve, and the other end connected to an exhaust passage downstream of the exhaust throttle valve;
A high-pressure EGR passage that takes a part of exhaust gas as a high-pressure EGR gas from an exhaust passage upstream of the turbine and recirculates the high-pressure EGR gas to an intake passage downstream of the compressor;
A high pressure EGR valve that is disposed in the high pressure EGR passage and adjusts the amount of high pressure EGR gas;
Second control means for controlling the exhaust throttle valve to the closed side and controlling the high pressure EGR valve to the open side while controlling the low pressure EGR valve to the closed side when the engine cooling water is below a predetermined temperature; ,
An exhaust gas recirculation device for an internal combustion engine. The exhaust gas recirculation apparatus for an internal combustion engine according to claim 1, further comprising a shutoff valve capable of shutting off the exhaust communication path. An exhaust communication passage blocking means for blocking the exhaust communication passage by the shut-off valve is provided when the operating state is high load and high rotation and the exhaust throttle valve is controlled to open. Item 3. An exhaust gas recirculation device for an internal combustion engine according to Item 2 . The shut-off valve is disposed at a connection portion between the low pressure EGR passage and the exhaust communication passage downstream of a portion where the low pressure EGR cooler is disposed, and communicates the upstream side and the downstream side of the low pressure EGR passage. together with the possible blocking the exhaust communication passages, according to claim 2 or 3, characterized in that the downstream can be interrupted in the low pressure EGR passage while communication with said exhaust communication passages and the upstream side of the low-pressure EGR passage 2. An exhaust gas recirculation device for an internal combustion engine according to 1. Wherein when the temperature of the exhaust gas is lower than the temperature of the engine cooling water, claim 1-4, characterized in that an exhaust inlet prohibiting means for prohibiting the flow of exhaust gas into the low-pressure EGR cooler 2. An exhaust gas recirculation device for an internal combustion engine according to item 1.

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