JP6098598B2 - Engine exhaust gas recirculation control device - Google Patents

Description

  The present invention belongs to a technical field related to an exhaust gas recirculation control device for an engine.

  Conventionally, an exhaust turbocharger having a turbine disposed in an exhaust passage of an engine and a compressor disposed in an intake passage, the exhaust passage downstream of the turbine, and the intake air upstream of the compressor. A low-pressure EGR passage connecting the passage, a low-pressure EGR valve disposed in the low-pressure EGR passage and changing a cross-sectional area of the low-pressure EGR passage, and a downstream side of a connection portion of the low-pressure EGR passage in the exhaust passage. 2. Description of the Related Art An engine exhaust gas recirculation control device that includes an exhaust shutter valve (exhaust throttle valve) that is disposed and changes the cross-sectional area of the exhaust passage is known. This exhaust gas recirculation control apparatus normally includes a high pressure EGR passage connecting the exhaust passage upstream of the turbine and the intake passage downstream of the compressor, and a high pressure EGR valve disposed in the high pressure EGR passage. Is further provided.

  An intercooler is disposed downstream of the compressor in the intake passage and upstream of the connection portion of the high pressure EGR passage. For this reason, the exhaust gas (low pressure EGR gas) recirculated to the intake passage by the low pressure EGR passage is cooled by the intercooler together with the intake air sucked into the intake passage.

  Here, in Patent Document 1, since condensed water is easily generated when the low pressure EGR gas is cooled by the EGR cooler provided in the low pressure EGR passage, the cooling to the EGR cooler is performed in order to prevent the generation of the condensed water. When the temperature of the water becomes equal to or higher than the dew point temperature of the low pressure EGR gas, the low pressure EGR gas starts to be recirculated.

JP 2014-9634 A

  As described above, since the low-pressure EGR gas is cooled by the intercooler together with the intake air, condensed water may be generated as in the case of cooling by the EGR cooler. That is, when the outside air temperature (that is, the temperature of the intake air taken into the intake passage) is low, the low pressure EGR gas is cooled by the intercooler if the amount of low pressure EGR, which is the amount of recirculation through the low pressure EGR passage, becomes excessive. Occasionally condensed water is likely to be generated.

  The present invention has been made in view of such points, and an object of the present invention is to suppress the generation of condensed water in the intercooler even when the low-pressure EGR gas is cooled by the intercooler together with the intake air. It is to do.

In order to achieve the above object, according to the present invention, an exhaust turbocharger having a turbine disposed in an exhaust passage of an engine and a compressor disposed in an intake passage, and the intake air downstream of the compressor. An intercooler disposed in the passage, a low pressure EGR passage connecting the exhaust passage downstream of the turbine and the intake passage upstream of the compressor, and return of the exhaust gas of the engine by the low pressure EGR passage. A low pressure EGR amount adjusting means for adjusting a low pressure EGR amount that is a flow rate, a high pressure EGR passage connecting the exhaust passage upstream of the turbine and the intake passage downstream of the intercooler, and the high pressure EGR A high pressure EGR amount adjusting means for adjusting the high pressure EGR amount, which is the recirculation amount of the exhaust gas of the engine through the passage. When, controls the low-pressure EGR amount by controlling the low-pressure EGR amount adjusting means, and a regulating means controller for controlling the high-pressure EGR amount by controlling the high-pressure EGR amount adjusting means, the exhaust of the engine For the reflux control device, the outside air temperature detecting means for detecting the outside air temperature, and the low pressure EGR amount is set to the low pressure EGR amount control value by the adjusting means control device according to the outside air temperature detected by the outside air temperature detecting means. with limits for, the time limit in the low-pressure EGR amount, further comprising a low-pressure EGR amount limiting means for the outside temperature is less the lower the the low-pressure EGR amount, the above-mentioned adjustment means control device, the rotational speed of the engine In the engine operating region represented by the load, the low load side whose load is lower than the first predetermined value is the high pressure at which the exhaust gas recirculates only by the high pressure EGR passage It is a GR region and is on the high load side above the first predetermined value and on the low load side higher than the second predetermined value larger than the first predetermined value by both the low pressure EGR passage and the high pressure EGR passage. A high-pressure / low-pressure EGR combined region that performs exhaust gas recirculation is provided, and a low-pressure EGR region that performs recirculation of the exhaust gas only by the low-pressure EGR passage is provided on the high load side that is greater than or equal to the second predetermined value. The low pressure EGR amount adjusting means and the high pressure EGR amount adjusting means are controlled, and when the outside air temperature detected by the outside air temperature detecting means is lower than a predetermined temperature, the high pressure EGR region is expanded toward the high load side and expanded. The low-pressure EGR amount adjusting means and the high-pressure EGR amount adjusting means are configured to be controlled so that the high-pressure / low-pressure EGR combined region is reduced by that amount. It was.

  With the above configuration, the low-pressure EGR amount limiting means decreases the low-pressure EGR amount as the outside air temperature decreases, so that the exhaust gas (low-pressure EGR gas) recirculated to the intake passage by the low-pressure EGR passage is intercooled together with the intake air. Even if cooled, it is possible to suppress the generation of condensed water.

Further, when the outside air temperature is lower than the predetermined temperature, the high pressure EGR region is expanded to the high load side, so that the exhaust gas recirculation through the low pressure EGR passage is less likely to occur, and the low pressure EGR amount restriction means restricts the low pressure EGR amount. The frequency can be reduced as much as possible.

In the exhaust recirculation control system of the engine, the upper Symbol adjusting means control apparatus, the above Symbol the low-pressure EGR amount by the low-pressure EGR amount limiting means limits an amount amount low-pressure EGR is decreased with respect to the low-pressure EGR amount control value, It is preferable that the high pressure EGR amount is increased.

  As a result, even if the low pressure EGR amount is limited by the low pressure EGR amount limiting means, the reduced amount of the low pressure EGR amount with respect to the low pressure EGR amount control value can be compensated by the high pressure EGR amount. Therefore, the total amount of the low pressure EGR and the amount of the high pressure EGR can be secured.

In the exhaust gas recirculation control device for the engine, the adjusting means control device is configured to control the low pressure EGR amount to a predetermined amount or less, and the low pressure EGR amount limiting means is an external temperature detected by the outside air temperature detecting means. air temperature when it is above the predetermined temperature or higher is configured not to perform the limit on the low-pressure EGR amount control value of the low-pressure EGR amount, it is preferable.

Thus, the adjusting means control device controls the low pressure EGR amount to be equal to or less than a predetermined amount, thereby ensuring the oxygen concentration of the gas sucked into the engine. If the outside air temperature is equal to or higher than a predetermined temperature, the intercooler can control the low pressure EGR amount below the predetermined amount while ensuring the oxygen concentration of the gas sucked into the engine without limiting the low pressure EGR amount. It becomes possible to suppress the generation of condensed water. On the other hand, when the outside air temperature is lower than the predetermined temperature, condensed water is likely to be generated by the intercooler. At this time, the amount of low-pressure EGR is limited, so that generation of condensed water by the intercooler can be suppressed. .

  In the exhaust gas recirculation control apparatus for the engine, the intercooler is configured to cool gas passing through the intercooler by supplying cooling water different from the engine cooling water by an electric water pump. The apparatus further includes a pump control device that controls the electric water pump so that the temperature of the gas after passing through the intercooler becomes a preset target temperature, and the low-pressure EGR amount limiting means is configured to detect the outside air temperature. It is preferable that the low-pressure EGR amount is limited to the low-pressure EGR amount control value in accordance with the outside air temperature detected by the means and the target temperature.

  As a result, the temperature of the gas after passing through the intercooler can sufficiently ensure the oxygen concentration of the gas (and hence the oxygen concentration of the gas sucked into the engine). Since the low pressure EGR amount is limited according to the outside air temperature and the target temperature (the temperature of the gas after passing through the intercooler), the low pressure EGR amount even if the temperature of the gas after passing through the intercooler changes. This restriction can be appropriately performed so that condensed water does not occur.

As described above, according to the exhaust gas recirculation control device for an engine of the present invention, the low pressure EGR amount is limited to the low pressure EGR amount control value by the adjusting means control device according to the outside air temperature, and the low pressure EGR amount is When the outside air temperature is lower, the amount of the low pressure EGR is decreased . Further, when the outside air temperature is lower than the predetermined temperature, the high pressure EGR region is expanded to the high load side, and the high pressure / low pressure EGR is increased by the increased amount. By controlling the low pressure EGR amount adjusting means and the high pressure EGR amount adjusting means so as to reduce the combined use area, even if the low pressure EGR gas that has been recirculated to the intake passage by the low pressure EGR passage is cooled by the intercooler. The generation of condensed water can be suppressed. Further, when the outside air temperature is lower than the predetermined temperature, the high pressure EGR region is expanded to the high load side, so that the exhaust gas recirculation through the low pressure EGR passage is less likely to occur. The frequency can be reduced as much as possible.

It is a figure showing a schematic structure of an engine controlled by an exhaust gas recirculation control device concerning an embodiment of the present invention. It is a block diagram which shows the structure of the control system of an exhaust gas recirculation | reflux control apparatus. It is a flowchart which shows the basic control of the engine by a control unit. It is a figure which shows roughly the "HP-EGR" area | region, the "LP-EGR" area | region, and the "HP / LP-EGR combined use" area | region in an engine operation area | region. It is a figure which shows the limiting value map showing the relationship between outside temperature and low pressure EGR amount limiting value. It is a flowchart which shows the restriction | limiting control of the low voltage | pressure EGR quantity by the low voltage | pressure EGR quantity restriction | limiting part. FIG. 5 is a diagram corresponding to FIG. 4, showing a case where the “HP-EGR” region is expanded on the high load side and the “HP / LP-EGR combined” region is contracted. It is a figure which shows the target temperature map showing the relationship between the request | requirement injection quantity and an engine speed, and the target temperature of the gas after passing an intercooler.

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

  FIG. 1 shows a schematic configuration of an engine 1 controlled by an exhaust gas recirculation control apparatus according to an embodiment of the present invention. The engine 1 is a diesel engine mounted on a vehicle, and includes a cylinder block 11 provided with a plurality of cylinders 11a (only one shown), a cylinder head 12 disposed on the cylinder block 11, An oil pan 13 is disposed below the cylinder block 11 and stores lubricating oil. In each cylinder 11a of the engine 1, a piston 14 is fitted and removably fitted. A top surface of the piston 14 is formed with a cavity that defines a deep dish combustion chamber 14a. The piston 14 is connected to the crankshaft 15 via a connecting rod 14b.

  In the cylinder head 12, an intake port 16 and an exhaust port 17 are formed for each cylinder 11a, and an intake valve 21 and an exhaust valve 22 that open and close the opening of the intake port 16 and the exhaust port 17 on the combustion chamber 14a side. Are arranged respectively.

  Further, the cylinder head 12 is provided with an injector 18 for injecting fuel and a glow plug 19 for warming the gas sucked into the cylinder 11a when the engine 1 is cold to enhance the ignitability of the fuel. . The injector 18 is disposed so that its fuel injection port faces the combustion chamber 14a from the ceiling surface of the combustion chamber 14a, and is configured to directly inject and supply fuel to the combustion chamber 14a.

  The injector 18 is supplied with fuel from a fuel tank 52 via a fuel supply system 51. The fuel supply system 51 includes an electric low-pressure fuel pump (not shown), a fuel filter 53, a high-pressure fuel pump 54, and a common rail 55 disposed in the fuel tank 52. The high-pressure fuel pump 54 pumps the low-pressure fuel supplied from the fuel tank 52 through the low-pressure fuel pump and the fuel filter 53 to the common rail 55 at a high pressure, and the common rail 55 supplies the pumped fuel to the common rail 55. Store with high pressure. When the injector 18 operates, the fuel stored in the common rail 55 is injected from the injector 18 into the combustion chamber 14a. Excess fuel generated in each of the low-pressure fuel pump, the high-pressure fuel pump 54, the common rail 55, and the injector 18 is supplied to the fuel tank 52 via the return passage 56 (excess fuel generated in the low-pressure fuel pump is directly). Returned.

  The high-pressure fuel pump 54 is driven by a rotating member (for example, a camshaft) of the engine 1. The high-pressure fuel pump 54 is provided with a pressure regulating valve composed of an electromagnetic valve. By this pressure regulating valve, the pressure of fuel supplied from the high-pressure fuel pump 54 to the common rail 55 (the pressure of fuel stored in the common rail 55), That is, the pressure (fuel pressure) of the fuel injected from the injector 18 can be adjusted.

  An intake passage 30 is connected to one side of the engine 1 so as to communicate with the intake port 16 of each cylinder 11a. On the other hand, an exhaust passage 40 for discharging burned gas (exhaust gas) from the combustion chamber 14a of each cylinder 11a is connected to the other side of the engine 1. The intake passage 30 and the exhaust passage 40 are provided with an exhaust turbocharger 61 that supercharges intake air (including exhaust gas recirculated by a low-pressure EGR passage 81 described later).

  An air cleaner 31 that filters intake air is disposed at the upstream end of the intake passage 30. On the other hand, a surge tank 34 is disposed near the downstream end of the intake passage 30. The intake passage 30 on the downstream side of the surge tank 34 is an independent passage branched for each cylinder 11a, and the downstream end of each independent passage is connected to the intake port 16 of each cylinder 11a.

  Between the air cleaner 31 and the surge tank 34 in the intake passage 30, the compressor 61 a of the exhaust turbocharger 61, the intake shutter valve 36, and an intercooler that cools the gas compressed by the compressor 61 a are sequentially arranged from the upstream side. A cooler 35 is provided. The intake shutter valve 36 is basically fully opened, but may have an opening smaller than the fully opened state in order to ensure a recirculation amount of exhaust gas through a high pressure EGR passage 71 described later. The intercooler 35 is disposed in the intake passage 30 on the downstream side of the compressor 61a, and cools the gas by supplying cooling water (cooling water different from the cooling water of the engine 1) by the electric water pump 91. It is configured as follows.

  The upstream portion of the exhaust passage 40 is constituted by an exhaust manifold having an independent passage branched for each cylinder 11a and connected to the outer end of the exhaust port 17 and a collecting portion where the independent passages gather. . On the downstream side of the exhaust manifold in the exhaust passage 40, in order from the upstream side, the turbine 61b of the exhaust turbocharger 61, an exhaust purification device 41 that purifies harmful components in the exhaust gas of the engine 1, and a silencer 42 Are arranged.

  The exhaust purification device 41 includes an oxidation catalyst 41a and a diesel particulate filter (hereinafter referred to as a filter) 41b, which are arranged in this order from the upstream side. The oxidation catalyst 41a has an oxidation catalyst supporting platinum or platinum added with palladium or the like, and promotes a reaction in which CO and HC in the exhaust gas are oxidized to generate CO2 and H2O. The filter 41b collects particulates such as soot contained in the exhaust gas of the engine 1. The filter 41b may be coated with an oxidation catalyst.

  The exhaust turbocharger 61 includes the compressor 61a disposed in the intake passage 30 as described above and the turbine 61b disposed in the exhaust passage 40 as described above. The rotation of the turbine 61b causes the compressor 61a connected to the turbine 61b to operate. A VGT throttle valve 62 is provided near the upstream side of the turbine 61b in the exhaust passage 40. By controlling the opening degree (throttle amount) of the VGT throttle valve 62, the flow rate of the exhaust gas to the turbine 61b is controlled. Thus, the rotational speed of the turbine 61b rotated by the exhaust gas flow, that is, the pressure ratio of the compressor 61a of the exhaust turbocharger 61 (from the compressor 61a to the gas pressure immediately before flowing into the compressor 61a) can be adjusted. The ratio of the gas pressure immediately after the outflow can be adjusted.

  The engine 1 is configured to recirculate a part of the exhaust gas from the exhaust passage 40 to the intake passage 30. A high pressure EGR passage 71 and a low pressure EGR passage 81 are provided to recirculate the exhaust gas.

  The high-pressure EGR passage 71 includes a portion of the exhaust passage 40 between the exhaust manifold and the turbine 61b of the exhaust turbocharger 61 (that is, a portion upstream of the turbine 61b of the exhaust turbocharger 61), and an intake passage. 30 is connected to a portion between the surge tank 34 and the intercooler 35 (that is, a portion downstream of the intercooler 35). The high pressure EGR passage 71 is provided with a high pressure EGR valve 73 that changes the cross-sectional area of the high pressure EGR passage 71. The high-pressure EGR valve 73 adjusts the exhaust gas recirculation amount (hereinafter referred to as high-pressure EGR amount) through the high-pressure EGR passage 71.

  The low pressure EGR passage 81 includes a portion of the exhaust passage 40 between the exhaust purification device 41 and the silencer 42 (that is, a portion downstream of the turbine 61b of the exhaust turbocharger 61), and an exhaust turbocharger in the intake passage 30. A portion between the compressor 61a of the machine 61 and the air cleaner 31 (that is, a portion upstream of the compressor 61a of the exhaust turbocharger 61) is connected. The low pressure EGR passage 81 is provided with a low pressure EGR cooler 82 for cooling the exhaust gas passing through the inside thereof. The low pressure EGR cooler 82 is configured to cool the exhaust gas by supplying cooling water of the engine 1. A low-pressure EGR valve 83 that changes the cross-sectional area of the low-pressure EGR passage 81 is disposed downstream of the low-pressure EGR cooler 82 in the low-pressure EGR passage 81.

  An exhaust shutter valve 43 is disposed downstream of the connection portion of the low-pressure EGR passage 81 in the exhaust passage 40 (and upstream of the silencer 42). The exhaust shutter valve 43 changes the cross-sectional area of the exhaust passage 40 at the portion where the exhaust shutter valve 43 is disposed, and when the cross-sectional area becomes small (the opening degree of the exhaust shutter valve 43 becomes small). The pressure at the connection portion of the low pressure EGR passage 81 in the exhaust passage 40 (inflow pressure of the exhaust gas into the low pressure EGR passage 81) becomes high, and the inflow pressure and outflow pressure of the exhaust gas into the low pressure EGR passage 81 (intake passage 30). The pressure difference between the low pressure EGR passage 81 and the pressure at the connecting portion) increases. Therefore, by controlling the opening degree of the low pressure EGR valve 83 and the exhaust shutter valve 43, the recirculation amount of the exhaust gas through the low pressure EGR passage 81 (hereinafter referred to as the low pressure EGR amount) is adjusted.

  The engine 1 is provided with an engine speed sensor 101 that detects the rotational speed of the engine 1 by detecting the rotational angle position of the crankshaft 15 (hereinafter referred to as engine speed).

  An air flow sensor 102 for detecting the flow rate of intake air (fresh air) sucked into the intake passage 30 is provided in the vicinity of the intake passage 30 downstream of the air cleaner 31 (upstream from the connection portion of the low pressure EGR passage 81). An intake air temperature sensor 103 that detects the temperature of the intake air (intake air temperature) is provided. This intake air temperature can be regarded as the outside air temperature around the vehicle. Further, the surge tank 34 is provided with an intake gas temperature sensor 104 that detects the temperature of the gas sucked into the cylinder 11 a of the engine 1, and in the vicinity of the downstream side of the intercooler 35 in the intake passage 30, An intake pressure sensor 105 for detecting the pressure (substantially the same as the gas pressure in the surge tank 34) is provided.

  Further, an exhaust pressure sensor 106 for detecting the pressure of the exhaust gas exhausted from the engine 1 is disposed upstream of the connection portion of the high pressure EGR passage 71 in the exhaust passage 40 (and downstream of the exhaust manifold). Yes. Further, an exhaust temperature sensor 107 that detects the temperature of the exhaust gas in the portion is provided between the exhaust purification device 41 and the low pressure EGR passage 81 in the exhaust passage 40.

  The cylinder block 11 of the engine 1 is provided with an engine water temperature sensor 108 that detects the temperature of the cooling water of the engine 1.

  The engine 1 configured as described above is controlled by the control unit 100. The control unit 100 is a controller based on a well-known microcomputer, and includes a central processing unit (CPU) that executes a program, a memory that is configured by, for example, a RAM or ROM, and stores a program and data, and an electrical signal And an input / output (I / O) bus.

  As shown in FIG. 2, the engine speed sensor 101, the air flow sensor 102, the intake air temperature sensor 103, the intake gas temperature sensor 104, the intake pressure sensor 105, the exhaust pressure sensor 106, the exhaust temperature sensor 107, the engine water temperature sensor 108, etc. The sensor value signal is input to the control unit 100. Further, the control unit 100 receives a sensor value signal of an accelerator opening sensor 110 (shown only in FIG. 2) that detects an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) of the vehicle.

  Based on the input signal, the control unit 100 controls the injector 18, the intake shutter valve 36, the exhaust shutter valve 43, the high-pressure fuel pump 54 (specifically, the pressure regulating valve), the VGT throttle valve 62, the high-pressure EGR valve 73, Controls the low pressure EGR valve 83, the electric water pump 91, and the like.

  Here, basic control of the engine 1 by the control unit 100 will be described based on the flowchart of FIG.

  In the first step S1, sensor values from various sensors are read, and in the next step S2, a target torque is set based on the accelerator opening by the accelerator opening sensor 110.

  In the next step S3, the required injection which is the amount of fuel to be injected from the injector 18 (the amount of fuel to be supplied to the engine 1 (cylinder 11a)) based on the target torque and the engine speed by the engine speed sensor 101. Set quantity and injection pattern. This injection pattern is the main injection for causing the main combustion, the injection before the main injection, the pre-injection for causing the pre-combustion, and the injection before the pre-injection to cause the pre-combustion. The pilot injection for facilitating, the post-injection for generating post-combustion after the main combustion, and the like are set at what timing and how much. In some cases, the injection amounts of pilot injection, pre-injection, and post-injection become zero, and in this case, the injection is not performed.

  In the next step S4, the pressure (fuel pressure) of the fuel injected from the injector 18 and the opening degree of the VGT throttle valve 62 are set based on the required injection amount and the engine speed.

  In the next step S5, a target intake oxygen concentration, which is a target value of the oxygen concentration of all intake gas sucked into the engine 1 (cylinder 11a), is set based on the required injection amount and the engine speed.

  In the next step S6, the ratio between the high pressure EGR amount and the low pressure EGR amount is based on the required injection amount, the engine speed, the intake air temperature by the intake air temperature sensor 103, and the engine water temperature by the engine water temperature sensor 108. Set EGR combination rate. This EGR combined use rate includes cases where the high pressure EGR amount or the low pressure EGR amount becomes zero.

  As a result of setting the EGR combined ratio in step S6, the exhaust gas recirculation is performed only by the high-pressure EGR passage 71 in the engine operation region represented by the engine speed and the engine load (corresponding to the required injection amount). “HP-EGR” region (high pressure EGR region), which is a region to be performed, “LP-EGR” region (low pressure EGR region), which is a region where exhaust gas recirculation is performed only by the low pressure EGR passage 81, and high pressure EGR passage FIG. 4 schematically shows an “HP / LP-EGR combined use” region (high pressure / low pressure EGR combined use region), which is a region where exhaust gas recirculation is performed by both 71 and the low pressure EGR passage 81. That is, the low load side where the load is lower than the first predetermined value is the “HP-EGR” region, the high load side which is equal to or higher than the first predetermined value, and the second predetermined value which is larger than the first predetermined value. On the low load side, the “HP / LP-EGR combined use” region is provided adjacent to the “HP-EGR” region. Further, the “LP-EGR” region is provided adjacent to the “HP / LP-EGR combined use” region on the high load side of the second predetermined value or more. In the “HP / LP-EGR combined use” region, the closer to the “LP-EGR” region, the lower the ratio of the high pressure EGR amount and the higher the ratio of the low pressure EGR amount.

In the next step S7, a target low pressure EGR amount that is a target value of the low pressure EGR amount is set based on the target intake oxygen concentration, the EGR combined ratio, and the exhaust oxygen concentration that is the oxygen concentration of the exhaust gas. Specifically, a target total EGR amount that is a target value of the total EGR amount of the low pressure EGR amount and the high pressure EGR amount is calculated from the target intake oxygen concentration and the exhaust oxygen concentration, and the target total EGR amount The target low pressure EGR amount is set from the EGR combined use rate. In the present embodiment, the exhaust oxygen concentration is a value calculated based on the target intake oxygen concentration and the amount of oxygen used for fuel combustion in the cylinder 11a. Instead of calculating the exhaust oxygen concentration, it may be detected exhaust oxygen concentration by 0 ₂ sensor provided in the exhaust passage 40.

  In the next step S8, based on the fresh air amount and the actual low pressure EGR amount, which is the actual value of the recirculation amount in the low pressure EGR passage 81, the oxygen concentration of the gas immediately before joining the high pressure EGR passage 71 in the intake passage 30 (fresh air The sum of the oxygen concentration and the oxygen concentration of the exhaust gas actually recirculated through the low pressure EGR passage 81 is calculated. Here, considering the time until the exhaust gas recirculated by the low pressure EGR passage 81 reaches just before the merge of the high pressure EGR passage 71 in the intake passage 30, the oxygen concentration immediately before the merge is calculated. Here, the fresh air amount is detected by the air flow sensor 102, and the actual low pressure EGR amount is obtained by subtracting the fresh air amount detected by the air flow sensor 102 from the total intake gas amount sucked into the engine 1 (cylinder 11a). (In the “HP / LP-EGR combined use” region, the actual high-pressure EGR amount that is the actual value of the recirculation amount through the high-pressure EGR passage 71 is also subtracted). The total intake gas amount can be calculated from the gas temperature detected by the intake gas temperature sensor 104 and the gas pressure detected by the intake pressure sensor 105, and the actual high pressure EGR amount is calculated with the intake pressure sensor 105. It can be calculated from the detected differential pressure with the exhaust pressure sensor 106 and the actual opening of the high pressure EGR valve 73.

  In the next step S9, the target high pressure EGR amount is set based on the target intake oxygen concentration, the exhaust oxygen concentration, the oxygen concentration of the gas just before the merging, and the total intake gas amount to the engine 1 (cylinder 11a). Set. That is, in step S8, the target high pressure EGR amount can be set in addition to the target low pressure EGR amount from the EGR combined ratio, but the exhaust gas recirculated through the low pressure EGR passage 81 (low pressure EGR gas) is exhausted. Since it takes time to reach from the port 17 to just before the high pressure EGR passage 71 joins the intake passage 30, the increase or decrease in the intake oxygen concentration is delayed by the time delay, and the excess or deficiency of the intake oxygen concentration is reduced. The target high pressure EGR amount is set so as to be supplemented by the high pressure EGR gas (the oxygen concentration of the high pressure EGR gas). That is, in the present embodiment, the target intake oxygen concentration set in advance according to the operating state of the engine 1 and the delay until the low pressure EGR gas reaches the junction of the high pressure EGR passage 71 in the intake passage 30 from the exhaust port 17. Calculated from the oxygen concentration of the pre-high pressure EGR merged gas (the gas flowing through the intake passage immediately upstream of the merged portion), the exhaust oxygen concentration, and the total intake gas amount to the engine 1 calculated in consideration of time. Is set as the target high pressure EGR amount. The oxygen concentration of the gas before the high-pressure EGR merging includes the fresh air amount, the actual low-pressure EGR amount, the oxygen concentration of the low-pressure EGR gas, and the delay time until the low-pressure EGR gas reaches the merging portion from the exhaust port 17. And calculated from

  In the next step S10, based on the above settings, the injector 18, the intake shutter valve 36, the exhaust shutter valve 43, the high pressure fuel pump 54 (pressure regulating valve), the VGT throttle valve 62, the high pressure EGR valve 73, and the low pressure EGR valve 83. The control amount of each actuator such as the electric water pump 91 is set.

  In the next step S11, each actuator is controlled based on the control amount, and then the process returns.

  Next, the opening control of the high pressure EGR valve 73, the low pressure EGR valve 83, and the exhaust shutter valve 43 by the control unit 100 will be described.

  The control unit 100 controls the opening degree of the high pressure EGR valve 73 so that the high pressure EGR amount becomes the preset target high pressure EGR amount (target high pressure EGR amount set in step S9). That is, the control unit 100 sets the opening degree of the high pressure EGR valve 73 to an opening degree at which the target high pressure EGR amount is obtained from the detected differential pressure between the intake pressure sensor 105 and the exhaust pressure sensor 106. The target high pressure EGR amount set in step S9 corresponds to the high pressure EGR amount control value by the control unit 100.

  Further, the control unit 100 opens the openings of the low pressure EGR valve 83 and the exhaust shutter valve 43 so that the low pressure EGR amount becomes a preset target low pressure EGR amount (target low pressure EGR amount set in step S7). To control. At that time, if the set target low pressure EGR amount is equal to or less than the low pressure EGR amount that can be recirculated when the low pressure EGR valve 83 and the exhaust shutter valve 43 are fully opened, the exhaust shutter valve 43 is fixed in the fully open state, The low pressure EGR amount is controlled by controlling the low pressure EGR valve 83 (the larger the target low pressure EGR amount, the larger the opening degree of the low pressure EGR valve 83). In addition, when the target low pressure EGR amount is larger than the low pressure EGR amount that can be recirculated when the low pressure EGR valve 83 and the exhaust shutter valve 43 are fully opened, the low pressure EGR valve 83 is fixed in the fully opened state, and the exhaust shutter valve 43 The low pressure EGR amount is controlled by control (the larger the target low pressure EGR amount, the smaller the opening degree of the exhaust shutter valve 43). In the present embodiment, the control unit 100 sets the target low pressure EGR amount to a predetermined amount Q0 or less (controls the low pressure EGR amount to a predetermined amount Q0 or less) in order to ensure the target intake oxygen concentration. Yes. The target low pressure EGR amount set in step S7 corresponds to the low pressure EGR amount control value by the control unit 100.

  In the present embodiment, the control unit 100 prevents the condensed water from being generated when the exhaust gas (low pressure EGR gas) recirculated to the intake passage 30 by the low pressure EGR passage 81 is cooled by the intercooler 35 together with the intake air. In addition, a low pressure EGR amount limiting unit 100a for limiting the low pressure EGR amount is provided.

  The low pressure EGR amount limiting unit 100a limits the low pressure EGR amount with respect to the low pressure EGR amount control value in accordance with the intake air temperature (that is, the outside air temperature) detected by the intake air temperature sensor 103. In the present embodiment, when the outside air temperature is lower than the predetermined temperature T0, the low pressure EGR amount restriction unit 100a determines the relationship between the outside air temperature and the low pressure EGR amount restriction value as shown in FIG. Is used to obtain a low pressure EGR amount limit value that is smaller than the predetermined amount Q0 using a limit value map (stored in the memory of the control unit 100), and the target set in step S7. When the low-pressure EGR amount Q1 (the low-pressure EGR amount control value) is larger than the obtained low-pressure EGR amount limit value, the low-pressure EGR amount limit value is set as a new target low-pressure EGR amount, thereby changing the low-pressure EGR amount. The amount is limited with respect to the low-pressure EGR amount control value. The control unit 100 controls the opening degrees of the low pressure EGR valve 83 and the exhaust shutter valve 43 so that the low pressure EGR amount becomes a new target low pressure EGR amount (the low pressure EGR amount limit value) whose setting has been changed. Thus, the low pressure EGR amount is limited with respect to the low pressure EGR amount control value. The low pressure EGR amount limit value is a value that does not generate condensed water even if the low pressure EGR gas is cooled by the intercooler 35 together with the intake air if the low pressure EGR amount is equal to or less than the low pressure EGR amount limit value.

  When the target low pressure EGR amount Q1 set in step S7 is equal to or less than the low pressure EGR amount limit value, the target low pressure EGR amount is not changed and the control unit 100 does not change the low pressure EGR amount as it is. The opening degree of the low pressure EGR valve 83 and the exhaust shutter valve 43 is controlled so that the EGR amount Q1.

  The low-pressure EGR amount limiting unit 100a does not limit the low-pressure EGR amount when the outside air temperature is equal to or higher than the predetermined temperature T0. As described above, when the outside air temperature is lower than the predetermined temperature T0, The EGR amount is limited to the low-pressure EGR amount control value.

  The low pressure EGR amount limit value becomes smaller as the outside air temperature is lower. As a result, when the low pressure EGR amount is limited, the low pressure EGR amount limiting unit 100a decreases the low pressure EGR amount as the outside air temperature is lower.

  If the outside air temperature is equal to or higher than the predetermined temperature T0, the predetermined temperature T0 is controlled so that the low-pressure EGR amount is equal to or less than the predetermined amount Q0 as described above, so that the low-pressure EGR amount is not limited. However, the temperature is such that it is possible to suppress the generation of condensed water in the intercooler 35.

  Here, the low pressure EGR amount restriction control by the low pressure EGR amount restriction unit 100a will be described based on the flowchart of FIG.

  In the first step S21, it is determined whether or not the outside air temperature is lower than the predetermined temperature T0. If the determination in step S21 is NO, the process returns as it is, while if the determination in step S21 is YES, Proceed to step S22.

  In step S22, the low pressure EGR amount limit value is obtained from the outside air temperature using the limit value map. In the next step S23, the target low pressure EGR amount Q1 set in step S7 is obtained in step S22. It is determined whether it is larger than the low pressure EGR amount limit value.

  If the determination in step S23 is NO, the process returns as it is. If the determination in step S23 is YES, the process proceeds to step S24, and the low pressure EGR amount limit value is set and changed as a new target low pressure EGR amount. Then return.

  As described above, when the low pressure EGR amount is restricted by the low pressure EGR amount restriction unit 100a, the target low pressure EGR amount decreases from the target low pressure EGR amount Q1, and the actual low pressure EGR amount decreases accordingly. However, in the present embodiment, as described above, the target high pressure EGR amount is calculated by considering the target intake oxygen concentration, the oxygen concentration of the pre-high pressure EGR gas that is calculated in consideration of the delay time, the exhaust oxygen concentration, and Since the value calculated based on the total intake gas amount to the engine 1 (cylinder 11a) is set, the difference between the oxygen concentration of the pre-high pressure EGR combined gas and the actual oxygen concentration of the pre-high pressure EGR combined gas is The high pressure EGR gas (the oxygen concentration of the high pressure EGR gas) can be compensated, whereby the low pressure EGR amount is controlled by the low pressure EGR amount restriction value (target low pressure EGR amount) by the restriction of the low pressure EGR amount by the low pressure EGR amount restriction unit 100a. Increase the high-pressure EGR amount by an amount reduced with respect to the amount Q1) (increase the target high-pressure EGR amount from the high-pressure EGR amount control value before limiting the low-pressure EGR amount) As a result, even if the low pressure EGR amount is limited, the actual value of the intake oxygen concentration of the gas sucked into the engine 1 (cylinder 11a) can be matched with the target value (target intake oxygen concentration). become. The same applies to the “LP-EGR” region, and the opening degree of the high-pressure EGR valve 73 may be more open than fully closed.

  In the present embodiment, when the outside air temperature is lower than the predetermined temperature T0, in order to make it difficult for the exhaust gas to recirculate through the low pressure EGR passage 81, as shown in FIG. The opening degree of the high pressure EGR valve 73, the low pressure EGR valve 83, and the exhaust shutter valve 43 is controlled so that the "HP / LP-EGR combined use" region is reduced by the amount of enlargement to the high load side. Thereby, the frequency of restriction of the low pressure EGR amount by the low pressure EGR amount restriction unit 100a can be reduced as much as possible.

Here, an example of the control of the electric water pump 91 will be described. In this example, in the target temperature map as shown in FIG. 8 (stored in the memory of the control unit 100), the required injection amount (unit: mm ³ ) and the engine speed (unit: rpm), The relationship with the target temperature (unit: ° C.) of the gas after passing through the intercooler 35 is set in advance. The target temperature of the gas is such a temperature that the oxygen concentration of the gas, that is, the target intake oxygen concentration can be ensured. Generally, the required injection amount is small with respect to the required injection amount. In this case, the target temperature becomes higher as the required injection amount increases, and in the case of a medium amount, the target temperature becomes constant. The target temperature is set to be as low as possible. On the other hand, for the engine speed, the target temperature is constant in the low speed range, and in the medium speed range, the target temperature is increased as the engine speed increases. The target temperature is set to be low as the temperature increases and the engine speed further increases.

  Then, the control unit 100 controls the electric water pump 91 () so that the temperature of the gas after passing through the intercooler 35 becomes the target temperature obtained from the required injection amount and the engine speed using the target temperature map. Specifically, the pump rotation speed) is controlled.

  In the case of the control of the electric water pump 91 as described above, the temperature of the gas after passing through the intercooler 35 changes according to the target temperature. If the gas temperature (the target temperature) is constant, the low-pressure EGR amount may be limited according to the outside air temperature as described above, but the gas temperature (the target temperature) changes. Preferably, the low pressure EGR amount is limited to the low pressure EGR amount control value according to the outside air temperature and the target temperature. That is, a limit value map as shown in FIG. 5 is set for each different target temperature, and the control unit 100 uses the limit value map to determine the low pressure EGR amount limit value from the outside air temperature and the target temperature. When the target low pressure EGR amount Q1 (the low pressure EGR amount control value) is larger than the calculated low pressure EGR amount limit value, the low pressure EGR amount limit value is set and changed as a new target low pressure EGR amount. Like that. If the target temperature is the same, the low pressure EGR amount limit value becomes smaller as the outside air temperature is lower, as described above. Further, the low pressure EGR amount limit value may be made smaller as the target temperature is lower if the outside air temperature is the same.

In this embodiment, the low pressure EGR valve 83 and the exhaust shutter valve 43 constitute a low pressure EGR amount adjusting means for adjusting the low pressure EGR amount, and the high pressure EGR valve 73 is a high pressure EGR amount for adjusting the high pressure EGR amount. The adjusting unit is configured, and the control unit 100 controls the low-pressure EGR amount adjusting unit and the high-pressure EGR amount adjusting unit to configure the adjusting unit control device that controls the low-pressure EGR amount and the high-pressure EGR amount. Become. The intake air temperature sensor 103 constitutes an outside air temperature detecting means for detecting the outside air temperature, and the low pressure EGR amount restriction unit 100a constitutes a low pressure EGR amount restriction means. Furthermore, the control unit 100 also constitutes a pump control device that controls the electric water pump 91.

  Therefore, in the present embodiment, the low-pressure EGR amount is limited with respect to the low-pressure EGR amount control value according to the outside air temperature, and the low-pressure EGR amount is reduced as the outside air temperature is lower when the low-pressure EGR amount is restricted. Therefore, even if the low pressure EGR gas that has been recirculated to the intake passage 30 by the low pressure EGR passage 81 is cooled by the intercooler 35 together with the intake air, the generation of condensed water can be suppressed. .

  The present invention is not limited to the embodiment described above, and can be substituted without departing from the spirit of the claims.

  For example, in the above embodiment, since the control unit 100 controls the low pressure EGR amount to be equal to or lower than the predetermined amount Q0, the low pressure EGR amount is not limited when the outside air temperature is equal to or higher than the predetermined temperature T0. However, if the low pressure EGR amount is not controlled to be equal to or lower than the predetermined amount Q0, the low pressure EGR amount is limited even when the outside air temperature is equal to or higher than the predetermined temperature T0. Also good.

  The above-described embodiments are merely examples, and the scope of the present invention should not be interpreted in a limited manner. The scope of the present invention is defined by the scope of the claims, and all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

The present invention includes an exhaust turbocharger having a turbine disposed in an exhaust passage of an engine and a compressor disposed in an intake passage, and an intercooler disposed in the intake passage on the downstream side of the compressor. A low-pressure EGR passage that connects the exhaust passage downstream of the turbine and the intake passage upstream of the compressor, and a low-pressure EGR amount that is a recirculation amount of the exhaust gas of the engine through the low-pressure EGR passage. Low pressure EGR amount adjusting means, a high pressure EGR passage connecting the exhaust passage upstream of the turbine and the intake passage downstream of the intercooler, and return of exhaust gas of the engine by the high pressure EGR passage and the high-pressure EGR amount adjusting means for adjusting the high-pressure EGR amount is the flow rate, the low-pressure EGR amount adjusting means Controlled and controls the low-pressure EGR amount, and controls the high-pressure EGR amount adjusting means and a regulating means controller for controlling the high-pressure EGR amount, it is useful in exhaust gas recirculation control apparatus for an engine.

1 Engine 30 Intake passage 35 Intercooler 40 Exhaust passage 43 Exhaust shutter valve (low pressure EGR amount adjusting means)
61 Exhaust turbocharger 61a Compressor 61b Turbine 71 High pressure EGR passage 73 High pressure EGR valve (High pressure EGR amount adjusting means)
81 Low pressure EGR passage 83 Low pressure EGR valve (Low pressure EGR amount adjusting means)
91 Electric Water Pump 100 Control Unit (Adjustment Means Control Device) (Pump Control Device)
100a Low pressure EGR amount limiting unit (low pressure EGR amount limiting means)
103 Intake air temperature sensor (outside air temperature detection means)

Claims (4)

An exhaust turbocharger having a turbine disposed in the exhaust passage of the engine and a compressor disposed in the intake passage; an intercooler disposed in the intake passage downstream of the compressor; A low pressure EGR passage for connecting the exhaust passage on the downstream side and the intake passage on the upstream side of the compressor, and a low pressure EGR for adjusting a low pressure EGR amount which is a recirculation amount of the exhaust gas of the engine through the low pressure EGR passage A high-pressure EGR passage that connects the amount adjusting means, the exhaust passage upstream of the turbine and the intake passage downstream of the intercooler, and a high pressure that is the recirculation amount of the exhaust gas of the engine through the high-pressure EGR passage and the high-pressure EGR amount adjusting means for adjusting the EGR amount, and controls the low-pressure EGR amount adjusting means Serial controls the low-pressure EGR amount, and a regulating means controller for controlling the high-pressure EGR amount by controlling the high-pressure EGR amount adjusting means and an exhaust recirculation control system of an engine,
An outside air temperature detecting means for detecting the outside air temperature;
In accordance with the outside air temperature detected by the outside air temperature detecting means, the low pressure EGR amount is limited with respect to the low pressure EGR amount control value by the adjusting means control device, and when the low pressure EGR amount is restricted, the outside air temperature is A low pressure EGR amount limiting means for reducing the low pressure EGR amount as the lower the pressure is ,
In the engine operating region represented by the engine speed and the load, the adjusting means control device performs recirculation of the exhaust gas only by the high pressure EGR passage on the low load side where the load is lower than the first predetermined value. A high-pressure EGR region is provided on both the low-pressure EGR passage and the high-pressure EGR passage on the high load side that is greater than or equal to the first predetermined value and on the low load side that is greater than the second predetermined value that is greater than the first predetermined value. A high-pressure / low-pressure EGR combined region for recirculating the exhaust gas is provided, and a low-pressure EGR region for recirculating the exhaust gas only by the low-pressure EGR passage is provided on the high load side that is equal to or greater than the second predetermined value. The low pressure EGR amount adjusting means and the high pressure EGR amount adjusting means are controlled, and when the outside air temperature detected by the outside air temperature detecting means is lower than a predetermined temperature, the high pressure EG Characterized in that the region is so enlarged and expanded amount corresponding the high-pressure / low-pressure EGR combined area thereof to the high load side is reduced, and is configured to control the low-pressure EGR amount adjusting means and the high-pressure EGR amount adjusting means The engine exhaust gas recirculation control device. The exhaust gas recirculation control device for an engine according to claim 1,
Upper Symbol adjusting means control apparatus, the above Symbol the low-pressure EGR amount by the low-pressure EGR amount limiting means limits an amount amount low-pressure EGR is decreased with respect to the low-pressure EGR amount control value, to increase the high-pressure EGR amount An exhaust gas recirculation control device for an engine, characterized in that it is configured. The engine exhaust gas recirculation control device according to claim 1 or 2,
The adjusting means control device is configured to control the low pressure EGR amount to a predetermined amount or less,
The low-pressure EGR amount limiting means, when the outside air temperature detected by the outside air temperature detection means is the predetermined temperature or higher is configured not to perform the limit on the low-pressure EGR amount control value of the low-pressure EGR amount An exhaust gas recirculation control apparatus for an engine. The engine exhaust gas recirculation control device according to any one of claims 1 to 3 ,
The intercooler is configured to cool a gas passing through the intercooler by supplying cooling water different from the cooling water of the engine by an electric water pump,
A pump controller for controlling the electric water pump so that the temperature of the gas after passing through the intercooler becomes a preset target temperature;
The low pressure EGR amount limiting means is configured to limit the low pressure EGR amount with respect to the low pressure EGR amount control value in accordance with the outside air temperature detected by the outside air temperature detecting means and the target temperature. An exhaust gas recirculation control apparatus for an engine.