JP5240514B2 - Engine exhaust gas recirculation system - Google Patents

Description

  The present invention relates to an exhaust gas recirculation device for an engine, and more particularly to an exhaust gas recirculation device that recirculates exhaust gas of an engine when a filter that collects exhaust particulates of the engine is regenerated.

  2. Description of the Related Art An exhaust gas recirculation (EGR) device is known in which part of engine exhaust gas is recirculated to the engine intake passage to reduce the content of nitrogen oxides (NOx) contained in the exhaust gas. There is also known an exhaust system provided with an oxidation catalyst and a filter for collecting exhaust particulates of the engine in the exhaust passage of the engine. In this system, when exhaust particulates collected in the filter exceed a predetermined amount, the fuel injection device for injecting fuel to the engine supplies unburned fuel to the oxidation catalyst to oxidize unburned fuel, and unburned fuel The filter is regenerated by burning the exhaust particulates collected in the filter by the oxidation heat. An exhaust system provided with an EGR device is described in Patent Document 1.

JP 2006-233947 A

  The EGR device described in Patent Document 1 is provided with an oxidation catalyst also on an EGR passage for recirculating engine exhaust, so that even if unburned fuel is mixed in the exhaust, the unburnt fuel is not removed by the oxidation catalyst. In order to prevent unburned fuel from being supplied to the engine.

  However, when an oxidation catalyst is provided on the EGR passage, the temperature in the EGR passage suddenly rises and there is a risk of causing a failure of the EGR valve for adjusting the amount of exhaust gas recirculated to the engine.

  Accordingly, the present invention has been made to solve the above-described problems. Even when the filter is regenerated, the exhaust gas is recirculated to the engine to obtain a sufficient NOx reduction effect and further provided in the EGR passage. An object of the present invention is to provide an exhaust gas recirculation device for an engine that can suppress a failure of an EGR valve.

In order to solve the above-described problem, the present invention provides an exhaust gas recirculation device that recirculates exhaust gas of an engine when regenerating a filter that collects exhaust particulates of the engine, and the exhaust passage of the engine under a predetermined condition. The regeneration means for regenerating the filter by burning the exhaust particulates collected in the filter by supplying unburned fuel to the first oxidation catalyst provided in the exhaust gas upstream of the first oxidation catalyst. A first EGR passage for branching from the exhaust passage to recirculate the exhaust to the engine, the first EGR passage configured to recirculate the exhaust to the engine intake passage via the second oxidation catalyst and the EGR valve; The second EGR passage is configured to recirculate exhaust gas to the intake passage of the engine via the second oxidation catalyst, the EGR cooler, and the EGR valve, and the temperature of the EGR valve. When the temperature of the EGR valve detected by the parameter value detecting means is lower than a predetermined temperature when the filter is being regenerated by the parameter value detecting means for detecting the parameter value to be regenerated, the exhaust gas is exhausted from the first EGR passage. And switching means for switching the first EGR passage and the second EGR passage so that the exhaust gas is recirculated from the second EGR passage when the temperature is equal to or higher than a predetermined temperature, cooling water temperature detection means for detecting the cooling water temperature of the engine, A third EGR passage adapted to recirculate exhaust gas to the intake passage of the engine via the EGR cooler and the EGR valve, and the switching means has a coolant temperature when the filter is not regenerated by the regenerating means. When the engine coolant temperature detected by the detection means is lower than the predetermined temperature, the exhaust gas is returned from the first EGR passage. And it is adapted to switch the first 1EGR passage and the 3EGR passage to reflux exhaust from the 3EGR passage when the predetermined temperature or higher.

According to the present invention configured as described above, when the temperature of the EGR valve is lower than a predetermined temperature when the filter is being regenerated by the regenerating means, the exhaust gas is recirculated from the first EGR passage, and the temperature of the EGR valve is determined. Can be switched so that the exhaust gas is recirculated from the second EGR passage. Then, when the temperature of the EGR valve is equal to or higher than a predetermined temperature, the unburned fuel mixed with the exhaust gas by regenerating means by recirculating the exhaust gas through the second oxidation catalyst, the EGR cooler, and the EGR valve Since the exhaust gas temperature can be lowered by the EGR cooler, the EGR valve can be prevented from being exposed to a high temperature, and the failure of the EGR valve can be suppressed. Further, according to the present invention configured as described above, when the filter is not regenerated by the regenerating means, if the engine coolant temperature is lower than the predetermined temperature, the exhaust gas is recirculated from the first EGR passage and cooled. When the water temperature is equal to or higher than a predetermined temperature, the recirculation passage can be switched so that the exhaust gas is recirculated from the third EGR passage. When the engine coolant temperature is lower than the predetermined temperature, the exhaust gas temperature can be raised and returned to the engine via the second oxidation catalyst and the EGR valve. Thus, the engine can be warmed up even when the regeneration means is not being executed.

  As described above, according to the exhaust gas recirculation device for an engine according to the present invention, a sufficient NOx reduction effect can be obtained by recirculating exhaust gas to the engine even during filter regeneration, and an EGR valve provided in the EGR passage. Can be prevented.

  Hereinafter, an exhaust gas recirculation device for an engine according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a vehicle engine and an exhaust gas recirculation device thereof according to the present embodiment. As shown in FIG. 1, the vehicle includes an engine 1, and the engine 1 is provided with an intake passage 3 and an exhaust passage 5.

  The engine 1 is a multi-cylinder diesel engine, and includes a fuel injection valve 9 provided in the cylinder head 7, and the fuel injection valve 9 injects fuel into the combustion chamber 11 of the engine 1. . The engine 1 is driven by introducing the air taken in from the intake passage 3 into the combustion chamber 11 and burning the fuel injected by the fuel injection valve 9. The exhaust of the engine 1 is exhausted to the outside of the vehicle through the exhaust passage 5. The engine 1 also includes a cooling water temperature sensor 13 that detects the water temperature in the engine 1 and a rotation speed sensor 15 that detects the rotation speed of the engine 1. The fuel injection valve 9, the coolant temperature sensor 13, and the rotation speed sensor 15 are connected to an ECU (Engine Control Unit) 17. The fuel injection valve 9 is configured such that the ECU 17 controls the fuel injection amount, the injection timing, and the like. In addition, the detection results of the coolant temperature sensor 13 and the rotation speed sensor 15 can be read by the ECU 17.

  From the upstream side of the intake passage 3, an air cleaner 19, an intake amount sensor 21 that detects the intake amount, a compressor 25 of the turbocharger 23, an intercooler 27 that cools the air, and an intake control for controlling the intake amount A valve 29 is provided. The air supplied to the intake passage 3 through the air cleaner 19 is pressurized by the compressor 25, cooled by the intercooler 27, and then supplied to the surge tank 31. An intake air temperature sensor 33 and an intake air pressure sensor 35 are disposed in the surge tank 31 so as to detect the temperature and pressure of the air supplied into the surge tank 31.

  Further, in the exhaust passage 5, a turbine 37 of the turbocharger 23 that is rotated by exhaust from the engine 1, a first oxidation catalyst 39, and a filter 41 for collecting particulates in the exhaust are upstream of the exhaust passage 5. It is arranged. Further, exhaust temperature sensors 43 and 45 are disposed on the upstream side of the exhaust passage and the downstream side of the exhaust passage of the first oxidation catalyst 39, respectively. In addition, the upstream side of the exhaust passage and the downstream side of the exhaust passage of the filter 41 are connected without passing through the filter 41, and the difference between the pressure on the upstream side of the filter 41 and the pressure difference on the downstream side is detected inside the filter 41. A pressure sensor 47 is provided.

  The fuel injection valve 9 can perform main injection control for injecting fuel so that the engine 1 generates an output and sub-injection control for injecting fuel so that the injected fuel is discharged into the exhaust passage 5 without being burned. It is like that.

  The filter 41 is provided on the downstream side of the exhaust passage of the first oxidation catalyst 39 and collects particulates contained in the exhaust. When particulates in the exhaust gas are collected by the filter 41, the exhaust gas from the engine 1 is then discharged outside the vehicle through a muffler (not shown), an exhaust pipe (not shown), and the like.

  Such a vehicle is configured to regenerate and control the filter 41 when a predetermined amount or more of fine particles are captured by the filter 41. In the regeneration control of the filter 41, the fuel injection valve 9 injects fuel during the expansion stroke of the engine 1, supplies unburned fuel to the first oxidation catalyst 39, oxidizes the unburned fuel by the first oxidation catalyst 39, This is performed by rapidly increasing the temperature of the first oxidation catalyst 39 on the downstream side of the exhaust passage. As a result, the exhaust particulates captured by the filter 41 are burned and the filter 41 is regenerated. In the regeneration control of the filter 41, the ECU 17 calculates the amount of particulates collected by the filter 41 based on the detection result of the differential pressure sensor 47, and the amount of particulates collected by the filter 41 is determined. This is done when the amount exceeds the fixed value.

  The exhaust passage 5 is connected to a main EGR passage 49 that recirculates exhaust from the engine 1 to the engine 1. The main EGR passage 49 extends from between the engine 1 in the exhaust passage 5 and the turbine 37 of the turbocharger 23 to the surge tank 31 in the intake passage 3. The main EGR passage 49 recirculates the exhaust of the engine 1 to the engine 1 through a route shown by an arrow A, and the main EGR passage 49 corresponds to the third EGR passage of the present invention. The main EGR passage 49 is provided with an EGR cooler 51 that cools the exhaust gas and an EGR valve 53 that adjusts the recirculation amount of the exhaust gas. The main EGR passage 49 is a passage for recirculating the exhaust of the engine 1 when the regeneration control of the filter 41 is not performed. Further, a gas temperature sensor 55 for obtaining a parameter related to the temperature of the EGR valve 53 is provided in the vicinity of the EGR valve 53.

  Further, the exhaust gas recirculation device for the engine is used for the regeneration control of the filter 41 in addition to the main EGR passage 49 used when the regeneration control of the filter 41 is not performed, and depends on the temperature of the EGR valve 53. Two EGR passages to be switched are provided. Specifically, the exhaust gas recirculation apparatus includes a low temperature EGR passage 57 used when the temperature of the EGR valve 53 is relatively low, and a high temperature EGR passage 59 used when the temperature of the EGR valve 53 is relatively high.

  The low temperature EGR passage 57 extends from the first switching valve 61 provided on the upstream side of the main EGR passage of the EGR cooler 51 to the EGR valve 53 by bypassing the EGR cooler 51. In addition, a second oxidation catalyst 63 is disposed in the low temperature EGR passage 57 so that the exhaust gas passing through the low temperature EGR passage 57 is oxidized. The exhaust gas passing through the low temperature EGR passage 57 is oxidized by the second oxidation catalyst 63 and reaches the EGR valve 53 as it is without passing through the EGR cooler 51, as indicated by an arrow B. The passage 57 corresponds to the first EGR passage of the present invention.

  The high temperature EGR passage 59 extends from the second switching valve 65 provided on the downstream side of the second oxidation catalyst 63 at the low temperature EGR passage to the space between the first switching valve 61 of the main EGR passage 49 and the EGR cooler 51. Exhaust gas passing through the high temperature EGR passage 59 is oxidized by the second oxidation catalyst 63 as shown by an arrow C, and then reaches the EGR valve 53 through the EGR cooler 51. The EGR passage 59 corresponds to the second EGR passage of the present invention.

  Next, the operation of the exhaust gas recirculation device 1 will be described with reference to FIGS. FIG. 2 is a flowchart showing the operation of the ECU 17, and FIG. 3 is a graph showing the relationship between the required torque T of the engine and the rotational speed Ne of the engine.

  When the engine 1 is started, the ECU 17 starts a series of processes. In S1, the ECU 17 acquires various parameters related to the rotational speed Ne of the engine 1, the accelerator opening degree θa, the differential pressure P between the upper and lower sides of the filter 41, the coolant temperature Tw of the engine 1, the reflux gas temperature Te, and the like. This process is executed by the ECU 17 reading detection values from the rotation speed sensor 15, the differential pressure sensor 47, the coolant temperature sensor 13, the gas temperature sensor 55, and the like.

  Next, in S2, the ECU 17 calculates the required torque T based on the rotational speed Ne of the engine 1 and the accelerator opening θa. Thereby, the ECU 17 can obtain the load of the engine 1. Next, in S <b> 3, the ECU 17 calculates the amount of exhaust particulate M captured by the filter 41 based on the differential pressure P. Thereby, ECU17 acquires the parameter for judging the necessity of filter regeneration control. These processes are performed by the ECU 17 based on the parameters read in S1.

  Next, in S4, the ECU 17 determines whether or not the exhaust particulate amount M captured by the filter 41 is equal to or smaller than a preset filter regeneration end determination threshold Me. The filter regeneration end determination threshold Me is a threshold when the amount of fine particles captured by the filter 41 by the filter regeneration control is decreased to a predetermined amount or less and the filter regeneration control is terminated. If the exhaust particulate amount M captured by the filter 41 is equal to or less than the filter regeneration end determination threshold Me, it is not necessary to perform filter regeneration control, or if the filter regeneration control is being performed, the filter 41 is captured by the filter 41. The filter regeneration control may be terminated because the amount of fine particles has decreased. On the other hand, when the exhaust particulate amount M is larger than the filter regeneration end determination threshold Me, the ECU 17 executes the processes after S5.

  In S5, the ECU 17 determines whether or not the exhaust particulate amount M is equal to or greater than the filter regeneration start determination threshold Ms (Ms> Me). The filter regeneration start determination threshold Ms is a threshold indicating that the filter regeneration control needs to be started. When the exhaust particulate amount M is equal to or greater than the filter regeneration start determination threshold Ms, it is necessary to start the filter regeneration control. Judge that there is. If it is determined that the filter regeneration control needs to be executed, the ECU 17 executes the processes after S6.

  In S6, the ECU 17 sets a value 1 as a regeneration execution flag to indicate that filter regeneration control is being executed, and then starts filter regeneration control in S7. The filter regeneration control is executed by the sub-injection control in which the ECU 17 controls the fuel injection valve 9 as described above and injects fuel from the fuel injection valve 9 in the expansion stroke of the engine 1. When the sub-injection control is performed, unburned fuel is supplied from the engine 1 to the first oxidation catalyst 39. Thereafter, the unburned fuel is oxidized by the first oxidation catalyst 39, thereby burning the particulates captured by the filter 41.

  Next, in S8, the ECU 17 sets the EGR rate based on the required torque T and the engine speed Ne.

  As shown in FIG. 3, EGR control is performed in the region A1 where the required torque T and the rotational speed Ne of the engine are lower than the predetermined values, while the EGR control is performed at the time of high rotation and high load (other than the region A1). Not performed. In the region A1, the EGR rate is low at a low rotation and low load when the required torque T is relatively small and the rotation speed Ne of the engine 1 is relatively slow, and the EGR rate is set high at a middle rotation during a load. The

  Next, in S9, the ECU 17 determines whether or not the recirculation gas temperature Te is lower than the recirculation gas temperature determination threshold value X. The reflux gas temperature determination threshold value X is a threshold value related to a temperature at which the EGR valve 53 is not damaged by the refluxed gas. When the recirculation gas temperature Te is higher than the recirculation gas temperature determination threshold value X, the ECU 17 executes the processes after S10.

  In S10, the ECU 17 sets the exhaust gas recirculation passage to the high temperature EGR passage 59 (arrow C). As a result, the exhaust gas is recirculated to the engine 1 via the second oxidation catalyst 63 and the EGR cooler 51. Next, in S11, the ECU 17 controls the first switching valve 61 and the second switching valve 65 in accordance with the set EGR passage. Next, in S12, the ECU 17 controls the EGR valve 53 according to the EGR rate. In S10, the high temperature EGR passage 59 is set and the exhaust gas is recirculated through the high temperature EGR passage 59, so that the unburned fuel mixed in the exhaust gas is oxidized by the second oxidation catalyst 63 by the filter regeneration control. Thus, abnormal combustion of the engine 1 due to recirculation of unburned fuel can be prevented, and further, the temperature of the exhaust gas raised by the second oxidation catalyst 63 is lowered by the EGR cooler 51 and the EGR valve 53 is damaged. Can be prevented.

  When it is determined in S9 that the recirculation gas temperature Te is lower than the recirculation gas temperature determination threshold X, in S13, the ECU 17 sets the EGR passage to the low temperature EGR passage 57 (arrow B), and then the steps after S11 are performed. Execute the process. When the low temperature EGR passage 57 is set, the exhaust gas passes through the second oxidation catalyst 63, bypasses the EGR cooler 51, and flows toward the EGR valve 53. By passing the exhaust gas through the EGR passage 57 at a low temperature, unburned fuel contained in the exhaust is oxidized by the second oxidation catalyst 63, and abnormal combustion of the engine 1 due to the supply of unburned fuel can be prevented. Further, the engine 1 can be warmed up by raising the temperature of the exhaust gas by the second oxidation catalyst 63.

  On the other hand, a case will be described in which it is determined in S4 that the amount M of exhaust particulate trapped by the filter 33 is equal to or smaller than a preset filter regeneration end determination threshold Me and it is not necessary to perform filter regeneration control. . In this case, the ECU 17 sets the EGR rate in S15 without performing the sub-injection control after setting the value 0 as the regeneration execution flag to indicate that the filter regeneration control is not being executed in S14. The process in S15 is the same as the process in S8, and an EGR rate corresponding to the engine load is set except during high-load high-speed rotation. Next, in S16, the ECU 17 determines whether or not the coolant temperature Tw is lower than the low water temperature determination threshold Y. When the cooling water temperature Tw is lower than the low water temperature determination threshold Y, the processing after S13 is executed to warm up the engine 1. On the other hand, when the cooling water temperature Tw is higher than the low water temperature determination threshold Y, it is not necessary to warm up the engine 1, so the ECU 17 sets the EGR passage to the main EGR passage 49 (arrow A). As a result, the exhaust gas is recirculated to the engine 1 without passing through the second oxidation catalyst 63. Thereafter, the ECU 17 executes the processes after S11.

  Further, if it is determined in S5 that the exhaust particulate amount M is not equal to or greater than the filter regeneration start determination threshold Ms and it is not necessary to start the filter regeneration control, the ECU 17 determines in S18 whether the regeneration execution flag indicates a value of 1. Judge whether or not. Thereby, it is possible to determine whether or not the filter regeneration control is being executed. If the regeneration execution flag indicates the value 1, it is determined that the filter regeneration control is being executed, and the processes after S6 are executed. On the other hand, if it is determined that the regeneration execution flag does not indicate the value 1, the processing after S14 is executed assuming that the filter regeneration control is not being performed.

  As described above, according to the embodiment of the present invention, the exhaust gas of the engine can be recirculated even during the regeneration control of the filter 41, and further, the EGR valve is switched by switching the EGR passage of the exhaust gas according to the temperature in the vicinity of the EGR valve 53. 53 failures can be suppressed.

1 is a block diagram showing an exhaust gas recirculation device for an engine and its surroundings according to an embodiment of the present invention. It is a flowchart which shows operation | movement of the exhaust gas recirculation apparatus of the engine by embodiment of this invention. It is a graph which shows the relationship between the required torque T of the engine by embodiment of this invention, and the rotational speed Ne of an engine.

Explanation of symbols

1 Engine 5 Exhaust passage 9 Fuel injection valve 13 Cooling water temperature sensor 17 ECU
49 Main EGR passage (3rd EGR passage)
51 EGR cooler 53 EGR valve 57 EGR passage at low temperature (first EGR passage)
59 EGR passage at high temperature (second EGR passage)
61 1st switching valve 63 2nd oxidation catalyst 65 2nd switching valve

Claims (1)

An exhaust gas recirculation device for recirculating engine exhaust when regenerating a filter that collects engine exhaust particulates,
Regeneration means for regenerating the filter by burning exhaust particulates collected in the filter by supplying unburned fuel to a first oxidation catalyst provided in an exhaust passage of the engine under a predetermined condition;
A first EGR passage for branching from the exhaust passage upstream of the first oxidation catalyst to recirculate exhaust gas to the engine, wherein the intake passage of the engine passes through a second oxidation catalyst and an EGR valve. A first EGR passage adapted to recirculate exhaust gas to,
A second EGR passage configured to recirculate exhaust gas to an intake passage of the engine via the second oxidation catalyst, an EGR cooler, and the EGR valve;
Parameter value detection means for detecting a parameter value related to the temperature of the EGR valve; and when the filter is regenerated by the regeneration means, the temperature of the EGR valve detected by the parameter value detection means is a predetermined temperature. Switching means for switching the first EGR passage and the second EGR passage so that the exhaust gas is recirculated from the first EGR passage when the temperature is less than the predetermined temperature, and the exhaust gas is recirculated from the second EGR passage when the temperature is higher than a predetermined temperature;
Cooling water temperature detecting means for detecting the cooling water temperature of the engine;
A third EGR passage adapted to recirculate exhaust gas to the intake passage of the engine via the EGR cooler and the EGR valve;
The switching means exhausts air from the first EGR passage when the engine coolant temperature detected by the coolant temperature detection means is lower than a predetermined temperature when the filter is not regenerated by the regeneration means. The engine exhaust gas recirculation device is configured to switch between the first EGR passage and the third EGR passage so that the exhaust gas is recirculated from the third EGR passage when the temperature is equal to or higher than a predetermined temperature .

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