JP6455243B2 - Engine control device - Google Patents

Description

  The present invention relates to an engine control device that includes an EGR passage that recirculates exhaust gas to an intake passage upstream of an intercooler.

  Conventionally, an EGR (Exhaust Gas Recirculation) system has been put to practical use as one technique for reducing the amount of nitrogen oxide (hereinafter referred to as NOx) generated in exhaust gas. In the EGR system, the exhaust gas is recirculated to the intake passage through the EGR passage connecting the exhaust passage and the intake passage, and flows again into the combustion chamber together with fresh air, thereby reducing the combustion temperature of the fuel or the oxygen concentration in the combustion chamber. The exhaust gas performance is enhanced by reducing the amount of NOx produced. An engine with a supercharger may be equipped with a dual EGR system with both a high pressure EGR system and a low pressure EGR system.

  In addition, an intercooler for cooling the intake air is provided in the intake passage of the engine, and the intake air is cooled by the intercooler to improve the charging efficiency and improve the engine output. However, when the intake air is cooled by the intercooler, water vapor contained in the intake air is condensed to generate water (hereinafter referred to as condensed water). If this condensed water is introduced into the cylinder together with the intake air, the combustion stability is lowered, the durability of the sensor and the engine is lowered, and the like. Therefore, conventionally, a structure for separating and discharging condensed water generated by an intercooler from intake air has been proposed (see, for example, Patent Document 1).

JP 2013-124563 A

  By the way, the amount of condensed water generated by the intercooler increases as the amount of water vapor contained in the intake air increases. Further, the exhaust gas contains water vapor generated by combustion, and the amount thereof is larger than that of fresh air. For this reason, when exhaust is introduced into the intake passage upstream of the intercooler and the mixture of the exhaust and fresh air (intake) is cooled in the intercooler, it is more than when only fresh air is cooled. Of condensed water is produced. The condensed water generated here is separated from the intake air on the downstream side of the intercooler and stored in the tank.

  However, if the amount of condensed water generated by the intercooler is large enough to exceed the capacity and capacity of the tank that separates and removes condensed water from the intake air, some of the condensed water may be introduced into the cylinder. There is sex. Further, in an environment where the temperature is below freezing, the condensed water may freeze in the passage for discharging the condensed water accumulated in the tank, and even if the condensed water can be separated from the intake air, there is a possibility that the condensed water will not be properly discharged.

  The present invention has been devised in view of such problems, and relates to an engine control device having an EGR passage that recirculates exhaust gas to an intake passage upstream of the intercooler, and effectively suppresses the generation of condensed water. One of the purposes is to do. The present invention is not limited to this purpose, and is a function and effect derived from each configuration shown in the embodiments for carrying out the invention described later, and other effects of the present invention are to obtain a function and effect that cannot be obtained by conventional techniques. Can be positioned.

  (1) An engine control device disclosed herein includes an intercooler that cools intake air flowing through an intake passage, an EGR passage that communicates an exhaust passage and the intake passage upstream of the intercooler, and the EGR An EGR valve that opens and closes communication of the passage, and a condensed water storage section that stores condensed water generated by the intercooler. The engine control device includes: a determination unit that determines whether or not the engine operating state is within a predetermined low load operating region; and the engine operating state that is within the predetermined low load operating region. And a control unit that fully closes the EGR valve when determined. When the intake air temperature is higher than a predetermined temperature, the determination unit sets an area where the engine load is equal to or lower than a predetermined load value as the predetermined low load operation area, and when the intake air temperature is equal to or lower than the predetermined temperature. Expands the predetermined low-load operation region so that the predetermined load value increases as the engine speed increases.

(2) Preferably, when the intake air temperature is equal to or lower than the predetermined temperature, the determination unit further expands the predetermined low-load operation region toward the high load side as the intake air temperature is lower than the predetermined temperature.
(3) The control unit preferably fully closes the EGR valve if the outside air temperature is equal to or lower than a predetermined first outside air temperature.

  (4) The control unit is configured such that the outside air temperature is a predetermined first outside air temperature or less and a second outside air temperature that is lower than the first outside air temperature, and the amount of condensed water stored in the condensed water storage unit is The EGR valve is fully closed when the outside air temperature is equal to or higher than the first determination value set smaller as the second outside air temperature is closer, and the EGR valve is also turned on when the outside air temperature is lower than the second outside air temperature. Fully closed is preferred.

  (5) The control unit fully closes the EGR valve when the intake air temperature is lower than the first intake air temperature lower than the predetermined temperature, and when the intake air temperature is equal to or higher than the first intake air temperature, If the amount of condensate stored in the condensate storage part is equal to or higher than the second determination value that is set higher as the intake air temperature is higher than the first intake air temperature, the EGR valve is preferably fully closed.

  In the disclosed engine control apparatus, the EGR valve can be appropriately fully closed, and the exhaust gas recirculated to the intake passage can be appropriately blocked, so that the generation of condensed water can be effectively suppressed. .

It is a mimetic diagram showing an engine and a control device concerning an embodiment. It is an example of the driving | operation map used with the control apparatus of FIG. 1, (a) is what set the prohibition area | region at the time of normal, (b) is what set the prohibition area | region at the time of low temperature. It is an example of the external temperature map used with the control apparatus of FIG. It is an example of the intake air temperature map used with the control apparatus of FIG. It is an example of a flowchart which shows the procedure of the prohibition determination by the control apparatus of FIG.

  An engine control apparatus as an embodiment will be described with reference to the drawings. The embodiment described below is merely an example, and there is no intention of excluding various modifications and technical applications that are not explicitly described in the following embodiment. Each configuration of the present embodiment can be implemented with various modifications without departing from the spirit of the present embodiment, and can be selected or combined as necessary.

[1. Device configuration]
The control device of the present embodiment is applied to a diesel engine 10 (hereinafter referred to as engine 10) mounted on a vehicle. FIG. 1 shows one of a plurality of cylinders 11 provided in the engine 10, but the other cylinders 11 have the same configuration. A piston 12 is slidably mounted in the cylinder 11, and the reciprocating motion of the piston 12 is converted into the rotational motion of the crankshaft 13 through the connecting rod.

  The cylinder head at the top of the cylinder 11 is provided with an injector 14 for fuel injection with its tip protruding toward the combustion chamber. High pressure fuel is directly injected from the injector 14 into the combustion chamber. The cylinder head is provided with an intake port 15 and an exhaust port 16, and an intake valve 17 and an exhaust valve 18 for opening and closing the ports 15 and 16 are provided.

  An intake manifold 19 (hereinafter referred to as an intake manifold 19) is provided on the upstream side of the intake port 15. The intake manifold 19 is provided with a surge tank 20 for temporarily storing air flowing toward the intake port 15. An intake passage 21 is connected to the upstream end of the intake manifold 19. An air filter 22 is interposed on the most upstream side of the intake passage 21, and fresh air filtered by the air filter 22 is introduced into the intake passage 21.

  On the other hand, an exhaust manifold 30 (hereinafter referred to as an exhaust manifold 30) is provided on the downstream side of the exhaust port 16. An exhaust passage 31 is connected to the downstream end of the exhaust manifold 30, and an exhaust purification device 32 is interposed in the exhaust passage 31. The exhaust purification device 32 includes a catalyst 32A and a filter 32B. The catalyst 32A has a function of purifying hydrocarbon (HC) components, carbon monoxide (CO), nitrogen oxides (NOx), etc. contained in the exhaust, and is, for example, an oxidation catalyst or a three-way catalyst. On the other hand, the filter 32B is a porous filter that collects particulate matter contained in the exhaust gas.

  The intake and exhaust system of the engine 10 is provided with a turbocharger 25 that supercharges intake air into the cylinder 11 using exhaust pressure. The turbocharger 25 is a supercharger interposed across both the intake passage 21 and the exhaust passage 31. The turbocharger 25 rotates the turbine with the exhaust pressure in the exhaust passage 31 and uses the rotational force to drive the compressor, thereby compressing the intake air on the intake passage 21 side and supercharging the engine 10. . The exhaust purification device 32 is provided in the exhaust passage 31 on the downstream side of the turbine of the turbocharger 25.

  An intercooler 26 for cooling the intake air is provided in the intake passage 21 on the downstream side of the compressor. The intercooler 26 is, for example, an air-cooled or water-cooled heat exchanger. A separation device 27 that separates the condensed water generated by the intercooler 26 from the intake air is provided in the intake passage 21 downstream of the intercooler 26. The separator 27 includes a separator 27A that separates condensed water from the intake air, a tank 27B (condensate water storage unit) that stores the separated condensed water, and a discharge passage 27C that discharges the condensed water accumulated in the tank 27B. And a valve 27D interposed in the discharge passage 27C. The separation device 27 is the same as the conventional configuration, and a detailed description thereof is omitted.

  The engine 10 according to the present embodiment is provided with a low pressure EGR (Exhaust Gas Recirculation) passage 33 and a high pressure EGR passage 35 that recirculate exhaust gas flowing through the exhaust passage 31 to the intake passage 21. The low pressure EGR passage 33 connects the exhaust passage 31 on the downstream side of the exhaust purification device 32 and the intake passage 21 on the upstream side of the compressor of the turbocharger 25. That is, the low pressure EGR passage 33 is connected to the intake passage 21 upstream of the intercooler 26.

  A low pressure EGR valve 24 is provided at a connection portion between the intake passage 21 and the low pressure EGR passage 33, and a low pressure throttle valve 23 is provided in the intake passage 21 between the low pressure EGR valve 24 and the air filter 22. Exhaust gas flowing through the low pressure EGR passage 33 is introduced into the intake passage 21 due to a pressure difference between the upstream end (exhaust passage 31) and the downstream end (intake passage 21) of the low pressure EGR passage 33. This pressure difference occurs when intake air is supercharged by the turbocharger 25 or when the opening of the low pressure throttle valve 23 is throttled. Further, the amount of exhaust gas introduced into the intake passage 21 (low-pressure recirculation gas amount) is adjusted according to the opening degree of the low-pressure EGR valve 24. The amount of the low-pressure recirculation gas increases as the opening of the low-pressure EGR valve 24 increases, and becomes zero when the opening is zero (closed valve). Each opening degree of the low pressure throttle valve 23 and the low pressure EGR valve 24 is controlled by the control device 1 described later. The low pressure EGR passage 33 is provided with an EGR cooler 34 for cooling the low pressure reflux gas.

  The high pressure EGR passage 35 connects the exhaust passage 31 upstream of the turbine of the turbocharger 25 and the intake passage 21 downstream of the compressor. A high pressure EGR valve 29 is provided at a connection portion between the intake passage 21 and the high pressure EGR passage 35, and a high pressure throttle valve 28 is provided in the intake passage 21 between the high pressure EGR valve 29 and the separation device 27. Exhaust gas flowing through the high pressure EGR passage 35 is introduced into the intake passage 21 due to a pressure difference between the upstream end and the downstream end of the high pressure EGR passage 35. This pressure difference occurs when intake air is not supercharged by the turbocharger 25 or when the opening of the high-pressure throttle valve 23 is throttled. Further, the amount of exhaust gas introduced into the intake passage 21 (high-pressure recirculation gas amount) is adjusted according to the opening degree of the high-pressure EGR valve 29. Each opening degree of the high-pressure throttle valve 28 and the high-pressure EGR valve 29 is also controlled by the control device 1. Note that an EGR cooler 36 for cooling the high-pressure reflux gas is also interposed in the high-pressure EGR passage 35.

  Therefore, the intake port 15 of the engine 10 has intake air (air mixture) in which fresh air, exhaust gas flowing from the low pressure EGR passage 33 (low pressure recirculation gas) and exhaust gas flowing from the high pressure EGR passage 35 (high pressure recirculation gas) are mixed. ) Is introduced. Thus, by mixing the low-pressure recirculation gas and the high-pressure recirculation gas into the intake air, an excessive exhaust temperature rise and NOx emission are suppressed.

  A rotation speed sensor 37 for detecting the rotation speed Ne of the engine 10 is provided in the vicinity of the crankshaft 13 of the engine 10. In the surge tank 20 of the intake manifold 19, an intake air temperature sensor 38 that detects the temperature of intake air introduced into the cylinder 11 (the temperature of intake air in the intake manifold 19 including the low pressure recirculation gas and the high pressure recirculation gas, hereinafter referred to as intake air temperature Ti). Is provided. In addition, the separation device 27 is provided with a detection unit 39 that detects the amount S of condensed water accumulated in the tank 27B. The detection unit 39 may be a simple device such as a floating type water level gauge, or may be a sensor that can detect the storage amount S with high accuracy. The engine 10 is also provided with a pressure sensor that detects the pressure of intake air, an air flow sensor that detects the flow rate of intake air, an air-fuel ratio sensor that detects the air-fuel ratio of intake air and exhaust gas, and the like (all not shown).

  The vehicle on which the engine 10 is mounted is provided with an outside air temperature sensor 40 that detects the outside air temperature Ta and an accelerator opening sensor 41 that detects the amount of depression of the accelerator pedal (accelerator opening AP) by the driver. The accelerator opening AP is a parameter corresponding to the driver's acceleration request and intention to start, in other words, a parameter correlated with the load Pe (torque, output request to the engine 10) of the engine 10. Each information detected by these sensors 37 to 41 is transmitted to the control device 1.

  The vehicle is provided with, for example, a control device 1 (Engine Electronic Control Unit) configured as an LSI device or an embedded electronic device in which a microprocessor, ROM, RAM, and the like are integrated. The control device 1 is an electronic control device that controls a wide range of systems such as an ignition system, a fuel system, and an intake / exhaust system related to the engine 10. Specific control objects of the control device 1 include the amount of fuel injected from the injector 14 and the injection timing, the opening amounts of the low pressure EGR valve 24, the high pressure EGR valve 29, the low pressure throttle valve 23, and the high pressure throttle valve 28. It is done.

[2. Control configuration]
In the present embodiment, detailed description will be given of prohibition determination for determining whether or not to prohibit control for introducing exhaust gas into the intake passage 21 through the low-pressure EGR passage 33 (hereinafter referred to as low-pressure EGR control). In the low pressure EGR control, each opening degree of the low pressure throttle valve 23 and the low pressure EGR valve 24 is controlled in order to control the amount of exhaust gas (low pressure recirculation gas) introduced from the low pressure EGR passage 33 to the intake passage 21. The prohibition determination is a determination as to whether or not to perform such low-pressure EGR control. Only when it is determined that the execution of the low pressure EGR control is permitted (not prohibited), the determination as to whether or not the low pressure EGR control is performed is performed.

  The low-pressure recirculation gas contains water vapor generated by combustion, and the amount thereof is larger than that of fresh air. Therefore, when the intake air including the low-pressure recirculation gas is cooled in the intercooler 26, more condensed water is generated than in the case where the intake air containing only fresh air is cooled. The condensed water is separated and removed from the intake air by the separation device 27, but when a large amount of condensed water exceeding the capability of the separation device 27 is generated, a part of the condensed water is introduced into the cylinder 11. there is a possibility. Further, when the outside air temperature is below freezing point, the condensed water may be frozen in the discharge passage 27C and the like, and even if separated by the separator 27A, there is a possibility that it is not properly discharged.

  Therefore, the control device 1 of the present embodiment performs the above-described prohibition determination so that low-pressure recirculation gas is not included in the intake air when there is a concern about the generation of a large amount of condensed water or freezing of condensed water. , Suppress the generation of condensed water itself. Then, the low pressure EGR control is performed after performing the prohibition determination, thereby appropriately introducing the low pressure reflux gas into the intake passage 21.

  The control device 1 includes a determination unit 2 and a control unit 3 as functional elements for performing such prohibition determination and low-pressure EGR control. Each of these elements may be realized by an electronic circuit (hardware), may be programmed as software, or some of these functions are provided as hardware, and the other part is software. It may be a thing.

  The determination part 2 performs said prohibition determination. The determination unit 2 according to the present embodiment performs three prohibition determinations, and when it is determined that any one of the prohibition determinations prohibits the low-pressure EGR control, a determination result “prohibit low-pressure EGR control” is issued, and all the prohibitions are determined. When it is determined in the determination that the low pressure EGR control is not prohibited, a determination result “permits low pressure EGR control” is issued. For example, when it is determined that the low pressure EGR control is prohibited in the first prohibition determination, a determination result “prohibit the low pressure EGR control” is issued without performing the second and third prohibition determinations. Here, “inhibiting the low pressure EGR control” means that the low pressure EGR valve 24 is fully closed.

  The first prohibition determination is a determination using the operation state of the engine 10 (operation region, specifically, the rotation speed Ne and the load Pe of the engine 10). The determination unit 2 determines whether or not the operating state of the engine 10 is within a predetermined low-load operation region, and prohibits the low-pressure EGR control if the operation state is within the predetermined low-load operation region (the low-pressure EGR valve 24 is completely turned off). It is determined that the low-pressure EGR control is not prohibited if it is outside the predetermined low-load operation region. This predetermined low-load operation region is not a certain (fixed) region, but is a region that can change according to the intake air temperature Ti, and is hereinafter referred to as a “prohibited region”.

The determination unit 2 of the present embodiment performs the first prohibition determination using the operation map illustrated in FIGS. 2 (a) and 2 (b). In these maps, the horizontal axis represents the rotational speed Ne and the vertical axis represents the load Pe. The hatched portion in the map is a prohibited region, and the non-hatched portion is a non-prohibited region (hereinafter, allowable region). It is said). FIG. 2A is an operation map in which a prohibited region is set when the intake air temperature Ti is higher than the predetermined temperature Tth (hereinafter referred to as normal time). During normal times, an area where the load Pe of the engine 10 is equal to or less than the predetermined load value Pe ₀ is set as a prohibited area. The predetermined load value Pe ₀ is a threshold value between the prohibition region and the allowable region. If the load Pe of the engine 10 is equal to or less than the threshold value (predetermined load value Pe ₀ ), it is determined that the low pressure EGR control is prohibited. The normal predetermined load value Pe ₀ is a constant value regardless of the rotational speed Ne, and is set in advance to a value corresponding to a load at which a sufficient amount of exhaust gas cannot be recirculated to the intake passage 21 only by the high pressure EGR passage 35, for example. The

  When the load Pe of the engine 10 is small, supercharging by the turbocharger 25 is not performed, and therefore, the opening degree control of the low pressure throttle valve 23 is necessary to generate a pressure difference. Therefore, by prohibiting the low pressure EGR control in the low load operation region, this opening degree control can be omitted, and the control configuration can be simplified. In the low load operation region, the exhaust gas is recirculated not through the low pressure EGR control but through the high pressure EGR passage 35, thereby suppressing an excessive exhaust temperature rise and NOx emission. The predetermined temperature Tth is a preset temperature, for example, the intake air temperature when the external air temperature Ta is 0 ° C. and 1 atm.

On the other hand, FIG. 2B is an operation map in which a prohibited region is set when the intake air temperature Ti is equal to or lower than a predetermined temperature Tth (hereinafter referred to as low temperature). At a low temperature, the forbidden area is expanded so that the predetermined load value Pe ₀ increases as the rotational speed Ne increases. That is, the prohibition area at low temperatures is substantially the same as the prohibition area at normal times in the extremely low rotation range, and is expanded to the high load side as the rotational speed Ne increases. In other words, the predetermined load value Pe ₀ as a threshold value between the prohibited area and the allowable area is set to the higher load side as the rotation speed is higher.

  The reason why the operation map at the low temperature is set in this way will be described. When the intake air temperature Ti is low, the outside air temperature Ta is usually low. For this reason, when the intake air containing the low-pressure recirculation gas containing a large amount of water vapor at a high temperature is cooled by the intercooler 26 to near the outside air temperature Ta, more condensed water is likely to be generated as compared with the case where the intake air temperature Ti is high. Become. Further, at a high load, since the supercharging pressure becomes high, a large amount of low-pressure recirculation gas is introduced, and the amount of cooling in the intercooler 26 is increased in order to increase the charging efficiency. Much condensed water is likely to be generated. In many cases, low-pressure reflux gas is not used on the low rotation side. Thus, at a low temperature, the rotation speed Ne is relatively high, and the higher the load, the easier it is to generate condensed water. Therefore, the prohibited region is set as described above to suppress the generation of condensed water.

Further, the prohibition region at the low temperature of the present embodiment is further expanded to the high load side as the intake air temperature Ti is lower than the predetermined temperature Tth (the larger the value obtained by subtracting the intake air temperature Ti from the predetermined temperature Tth). . That is, when the intake air temperature Ti is lower than the predetermined temperature Tth, the lower the intake air temperature Ti, the slope of the threshold value (predetermined load value Pe ₀ ) between the prohibited region and the allowable region (the load Pe with respect to the increase amount of the rotational speed Ne). The prohibition area is set so that the increase amount) increases. In the setting of the prohibited area, the engine room changes depending on changes in atmospheric pressure (meteorological conditions), hard deterioration of the low pressure EGR passage 33 and the EGR cooler 34, and the running state by using the intake air temperature Ti instead of the outside air temperature Ta. Control robustness is improved because it can be controlled including various disturbances such as heat exchange between the internal air and the intake air through the intake pipe wall surface.

For example, when the intake air temperature Ti is slightly lower than the predetermined temperature Tth, the threshold (predetermined load value Pe ₀ ) between the normal prohibition area and the permission area indicated by the broken line is expanded to the part indicated by the two-dot chain line. Set as a prohibited area at low temperatures. Further, when the intake air temperature Ti is lower than this, the threshold value (predetermined load value Pe ₀ ) indicated by the broken line is expanded to the portion indicated by the alternate long and short dash line, and is set as the prohibited region at the low temperature. When the intake air temperature Ti is further lower than this, the threshold value (predetermined load value Pe ₀ ) indicated by the broken line is expanded to the portion indicated by the solid line and is set as the prohibited region at the low temperature. In FIG. 2B, three forbidden areas at low temperatures are illustrated as being overlapped, but the forbidden areas at low temperatures are gradually expanded as the intake air temperature Ti decreases.

In the control device 1 of the present embodiment, a plurality of operation maps in which prohibited areas are set for each intake air temperature Ti are provided in advance. The determination unit 2 selects an operation map corresponding to the intake air temperature Ti detected by the intake air temperature sensor 38 from the plurality of operation maps, and acquires an appropriate prohibition region corresponding to the intake air temperature Ti. That is, the determination unit 2 selects the operation map shown in FIG. 2A if the intake air temperature Ti is higher than the predetermined temperature Tth, thereby setting the area below the predetermined load value Pe ₀ as the prohibited area. Further, when the intake air temperature Ti is equal to or lower than the predetermined temperature Tth, the determination unit 2 selects the operation map shown in FIG. 2B in which the prohibited region is set according to the intake air temperature Ti, so that the rotational speed Ne is The predetermined low load operation region (prohibited region) is expanded so that the predetermined load value Pe ₀ increases as the value increases.

  And the determination part 2 determines whether the driving | running state of the engine 10 is in a prohibition area | region. If the determination unit 2 determines that the low pressure EGR control is prohibited in the first prohibition determination, the determination result “inhibit the low pressure EGR control” is performed without performing the following second and third prohibition determinations. This is transmitted to the control unit 3. On the other hand, if it is determined in the first prohibition determination that the low pressure EGR control is not prohibited, a second prohibition determination is performed.

  The second prohibition determination is a determination using the outside air temperature Ta detected by the outside air temperature sensor 40 and the condensate water storage amount S detected by the detection unit 39. The determination unit 2 of the present embodiment performs prohibition determination by applying the outside air temperature Ta and the storage amount S to the outside air temperature map set in the control device 1 in advance. In the outside air temperature map, a range (prohibited range) in which the low pressure EGR control should be prohibited is set according to the outside air temperature Ta and the storage amount S. The determination unit 2 determines that the low-pressure EGR control is prohibited (the low-pressure EGR valve 24 is fully closed) if the outside air temperature Ta and the storage amount S are within the prohibited range of the outside air temperature map. If so, it is determined that the low pressure EGR control is not prohibited.

FIG. 3 is an example of an outside air temperature map. In this map, the horizontal axis represents the outside air temperature Ta, and the vertical axis represents the storage amount S. The hatched portion in the map is the prohibited range, and the non-hatched portion is the prohibited range (hereinafter, the allowable range). It is said). In the outside air temperature map of FIG. 3, the prohibited range and the allowable range are basically set with a predetermined first outside air temperature Ta ₁ as a boundary line. Specifically, a range higher than the first outside air temperature Ta ₁ is set as an allowable range, and a range below the first outside air temperature Ta ₁ is set as a prohibited range except for a part. This part is set within an allowable range.

The first outside air temperature Ta ₁ is a temperature in the vicinity of 0 ° C. where there is a concern about freezing of condensed water or an increase in the amount of generated water. When the outside air temperature Ta is equal to or lower than the first outside air temperature Ta ₁ , the introduction of the low-pressure recirculation gas is basically prohibited because there is a possibility that the condensed water may be frozen or the generation amount may be increased. However, even when the outside air temperature Ta is equal to or lower than the first outside air temperature Ta ₁ , it may be preferable to introduce a low-pressure recirculation gas from the viewpoint of suppressing NOx emission and improving exhaust gas performance.

Therefore, the outside air temperature map of the present embodiment provides only a part of the allowable range in the range of the first outside air temperature Ta ₁ or less, the water storage amount S is relatively small, and the low pressure is low only when the possibility of freezing is low. The introduction of reflux gas is allowed. This part is the outside air temperature Ta is a second outdoor air temperature Ta ₂ or more and the first outside air temperature Ta ₁ below lower than the first outside air temperature Ta _1, water volume S is in the range of the less than a determination value De ₁ Yes (Ta ₂ ≦ Ta ≦ Ta ₁ and S <De ₁ ). The second outside air temperature Ta ₂ is a temperature that is lower by about 20 ° C. than the first outside air temperature Ta ₁ , and is assumed to be a temperature at which, for example, the temperature of the tank 27B and the discharge passage 27C is surely higher than 0 ° C. Is set.

The first determination value De ₁ is a boundary line between the prohibited range and tolerance range of the first outside air temperature Ta ₁ below temperature range is set to a predetermined amount Sa when the first outside air temperature Ta _1, the It is set closer to the two outside air temperature Ta ₂ small. The first determination value De ₁ of the present embodiment is set to linearly decrease from a predetermined amount Sa at the first outside air temperature Ta ₁ and become zero at the second outside air temperature Ta ₂ . The predetermined amount Sa is a value corresponding to, for example, a capacity of about 30% of the maximum capacity in consideration of the positional relationship between the intake side of the tank 27B and the water storage surface (water surface height from the bottom surface of the tank 27B). . Note that the values of the first outside air temperature Ta ₁ , the second outside air temperature Ta ₂ , and the predetermined amount Sa are examples, and the specific values take into consideration the performance of the intercooler 26, the performance of the separation device 27, and the like. It is set by experiment or simulation.

Therefore, when the outside air temperature Ta is equal to or higher than the second outside air temperature Ta ₂ and equal to or lower than the first outside air temperature Ta ₁ , the determination unit 2 prohibits the low pressure EGR control if the storage amount S is equal to or higher than the first determination value De _1. If the storage amount S is less than the first determination value De ₁ , it is determined that the low pressure EGR control is not prohibited. The determination unit 2 determines that the low-pressure EGR control is prohibited regardless of the water storage amount S if the outside air temperature Ta is lower than the second outside air temperature Ta ₂ , and the outside air temperature Ta is higher than the first outside air temperature Ta _1. For example, it is determined that the low pressure EGR control is not prohibited regardless of the water storage amount S. If the determination unit 2 determines that the low pressure EGR control is prohibited in the second prohibition determination, the determination result “inhibit the low pressure EGR control” is sent to the control unit 3 without performing the next third prohibition determination. introduce. On the other hand, if it is determined in the second prohibition determination that the low pressure EGR control is not prohibited, a third prohibition determination is performed.

  The third prohibition determination is a determination using the intake air temperature Ti detected by the intake air temperature sensor 38 and the stored amount S of condensed water detected by the detection unit 39. The determination unit 2 of the present embodiment performs prohibition determination by applying the intake air temperature Ti and the storage amount S to the intake air temperature map set in the control device 1 in advance. In the intake air temperature map, a range (prohibited range) in which low pressure EGR control should be prohibited is set according to the intake air temperature Ti and the storage amount S. The determination unit 2 determines that the low pressure EGR control is prohibited if the state of the intake air temperature Ti and the storage amount S is within the prohibited range of the intake air temperature map, and determines that the low pressure EGR control is not prohibited if the state is outside the prohibited range. .

FIG. 4 is an example of an intake air temperature map. This map is the intake temperature Ti on the horizontal axis and the storage amount S on the vertical axis. The hatched part in the map is the prohibited range, and the unshaded part is not the prohibited range (hereinafter, the allowable range). It is said). In the intake air temperature map of FIG. 4, the prohibited range and the allowable range are set with a predetermined second determination value De ₂ as a boundary line. Specifically, the lower temperature side than the second determination value De ₂ is set as a prohibited range, and the higher temperature side than the second determination value De ₂ is set as an allowable range.

Second determination value De ₂ is a boundary line between the prohibited range and tolerance range of the first intake air temperature Ti ₁ or more temperature region, is set to zero on the first intake air temperature Ti _1, a high intake air temperature Ti It is set so large. The second determination value De ₂ of the present embodiment increases linearly from the value at the first intake air temperature Ti ₁ (that is, zero), and the intake air temperature Ti ₀ (hereinafter, referred to as the first outside air temperature Ta ₁₎ . The inclination is set so that the storage amount S becomes the predetermined amount Si at a predetermined intake temperature Ti ₀ ) and extends to the maximum value of the storage amount S (the maximum capacity of the tank 27B).

That is, if the intake air temperature Ti is high, the introduction of the low-pressure recirculation gas is permitted even if the storage amount S is large, and the introduction of the low-pressure recirculation gas is prohibited with a smaller storage amount S as the intake air temperature Ti is low. This is because the amount of saturated water vapor is smaller as the intake air temperature Ti is lower, so that condensed water is more likely to be generated. The first intake air temperature Ti is a temperature lower than the predetermined temperature Tth, and is preferably higher than the second external air temperature Ta _{2 and} lower than the first external air temperature Ta _1. The temperature is around 10 ℃. In addition, the predetermined amount Si is set to a value corresponding to a capacity of about 30% of the maximum capacity of the tank 27B, for example, similar to the predetermined amount Sa. The values of the first intake air temperature Ti ₁ , the predetermined intake air temperature Ti ₀ , and the predetermined amount Si are also examples. For example, the predetermined intake air temperature Ti ₀ may be a temperature different from the first outside air temperature Ta _1, and the predetermined amount Si may be a value different from the predetermined amount Sa. These values are set as appropriate.

In the temperature range where the intake air temperature Ti is equal to or higher than the first intake air temperature Ti ₁ and equal to or lower than the predetermined intake air temperature Ti _0, a range where the storage amount S is less than the second determination value De ₂ is set as an allowable range. Similar to the outside air temperature map of FIG. 3, this is provided from the viewpoint of suppressing the NOx emission amount and improving the exhaust gas performance. That is, the allowable range is set with priority given to the improvement of exhaust gas performance rather than the suppression of the amount of condensed water produced.

Therefore, when the intake air temperature Ti is equal to or higher than the first intake air temperature Ti ₁ , the determination unit 2 determines that the low pressure EGR control is prohibited if the storage amount S is equal to or higher than the second determination value De ₂ . If the intake air temperature Ti is lower than the first intake air temperature Ti _1, it is determined that the low pressure EGR control is prohibited regardless of the water storage amount S. When the determination unit 2 makes these determinations, the determination unit 2 transmits a determination result “prohibit low-pressure EGR control” to the control unit 3. On the other hand, the determination section 2 determines that the storage amount S is less than the second determination value De _2, it does not prohibit the low-pressure EGR control. In this case, since the determination unit 2 determines that the low pressure EGR control is not prohibited in all three prohibition determinations, the determination unit 2 outputs a determination result “permits the low pressure EGR control” and transmits this determination result to the control unit 3. To do.

  The control unit 3 performs the low-pressure EGR control according to the determination result in the determination unit 2 and the operating state of the engine 10. When the determination result “prohibit low pressure EGR control” is transmitted from the determination unit 2, the control unit 3 prohibits the low pressure EGR control regardless of the operating state of the engine 10. That is, in this case, the opening degree of the low pressure EGR valve 24 is controlled to zero (fully closed), and the opening degree of the low pressure throttle valve 23 is controlled to be fully opened.

That is, the control unit 3 of the present embodiment fully closes the low pressure EGR valve 24 when the operation state of the engine 10 is within a predetermined low load operation region (prohibition region). In addition, the control unit 3 turns off the low-pressure EGR valve 24 when the outside air temperature Ta is the first outside air temperature Ta ₁ or lower and the second outside air temperature Ta ₂ or higher and the storage amount S is the first determination value De ₁ or higher. Even when the outside air temperature Ta is lower than the second outside air temperature Ta _{2, the} low pressure EGR valve 24 is fully closed. Further, the control unit 3, a low-pressure EGR valve 24 when the intake air temperature Ti is first less than a intake air temperature Ti ₁ is fully closed, the intake air temperature Ti is storage amount S is second in the case of the first intake air temperature Ti ₁ or more If the determination value is De ₂ or more, the low pressure EGR valve 24 is fully closed.

  On the other hand, when the determination result “permit low pressure EGR control” is transmitted from the determination unit 2, the control unit 3 determines whether or not to perform the low pressure EGR control based on the operating state of the engine 10. . And when it determines with implementing low pressure EGR control, low pressure EGR control is implemented. That is, in this case, in order to introduce the low-pressure recirculation gas into the intake passage 21, the opening degrees of the low-pressure throttle valve 23 and the low-pressure EGR valve 24 are controlled. As described above, by performing the prohibition determination prior to the execution determination of the low pressure EGR control, the generation of condensed water is effectively suppressed.

[3. flowchart]
FIG. 5 is a flowchart illustrating the above-described prohibition determination procedure. The determination unit 2 of the control device 1 is repeatedly executed at a predetermined calculation cycle.
In step A1, each information detected by each sensor 37-41 etc. is inputted into control device 1. In step A2, an operation map is selected according to the intake air temperature Ti, and in the subsequent step A3, it is determined whether or not the operation state of the engine 10 is within the prohibited region using the operation map (first operation). Prohibition judgment).

  If it is determined in step A3 that the area is within the prohibited area, the process proceeds to step A7. If it is determined that the area is outside the prohibited area (in the allowable area), the process proceeds to step A4. In step A4, the outside air temperature Ta and the water storage amount S are applied to the outside air temperature map, and it is determined whether or not they are within the prohibited range (second prohibition determination). If it is determined in step A4 that it is within the prohibited range, the process proceeds to step A7, and if it is determined that it is outside the prohibited range (within the allowable range), the process proceeds to step A5.

  In step A5, the intake air temperature Ti and the water storage amount S are applied to the intake air temperature map, and it is determined whether or not they are within the prohibited range (third prohibition determination). If it is determined in step A5 that it is within the prohibited range, the process proceeds to step A7, and if it is determined that it is outside the prohibited range (within the allowable range), the process proceeds to step A6. In step A6, a determination result “permit low pressure EGR control” is issued, and the flow returns. On the other hand, in step A7, a determination result “prohibit low-pressure EGR control” is issued, and this flow is returned.

[4. effect]
Prior to the determination of whether or not to implement the low pressure EGR control, the control device 1 determines whether or not the operating state of the engine 10 is in the prohibited region (predetermined low load operation region). If it is within, the low pressure EGR valve 24 is fully closed. Further, the prohibited area used for this determination is changed according to the intake air temperature Ti. Specifically, if the intake air temperature Ti is higher than the predetermined temperature Tth, the region where the predetermined load value Pe is ₀ or less is set as the prohibited region. If the intake air temperature Ti is equal to or lower than the predetermined temperature Tth, the predetermined load value is increased as the rotational speed Ne is higher. The prohibited area is expanded so that Pe ₀ increases. By performing the determination using the prohibited region set in this way, the low-pressure EGR valve 24 control can be appropriately fully closed, and the exhaust gas recirculated to the intake passage 21 can be appropriately shut off. Water generation can be effectively suppressed.

  In the control device 1 described above, when the intake air temperature Ti is equal to or lower than the predetermined temperature Tth, the lower the intake air temperature Ti, the more the prohibited region is expanded to the high load side, and the prohibition determination of the low pressure EGR control is performed using the prohibited region. . As a result, in a state where the intake air temperature Ti is low and condensed water is easily generated, the low pressure EGR valve 24 can be appropriately fully closed, so that generation of condensed water can be more effectively suppressed.

In the control device 1 described above, in addition to the first prohibition determination, the second prohibition determination is performed using the outside air temperature Ta and the stored amount S of condensed water. Specifically, when the outside air temperature Ta is not less than the second outside air temperature Ta _{2 and not} more than the first outside air temperature Ta ₁ and the stored water amount S is not less than the first determination value De ₁ , it is determined that the low pressure EGR control is prohibited. The low pressure EGR valve 24 is fully closed. Further, even when the outside air temperature Ta is lower than the second predetermined temperature Ta ₂ , it is determined that the low pressure EGR control is prohibited, and the low pressure EGR valve 24 is fully closed. Due to the latter determination, in an environmental state in which an increase in the amount of condensed water or freezing of the condensed water is a concern, the low-pressure EGR valve 24 is appropriately fully closed, so that the generation of condensed water itself is effectively suppressed. be able to. Further, according to the former determination, when the storage amount S does not have a margin, the generation of condensed water itself can be appropriately suppressed. When the storage amount S has a margin, the generation amount of NOx is suppressed more than the generation of condensed water. By giving priority, exhaust gas performance can be improved.

In the control device 1 described above, in addition to the first prohibition determination, a third prohibition determination is performed using the intake air temperature Ti and the condensate storage amount S. Specifically, when the intake air temperature Ti is lower than the first intake air temperature Ti _1, it is determined that the low pressure EGR control is prohibited, the low pressure EGR valve 24 is fully closed, and when the intake air temperature Ti is equal to or higher than the first intake air temperature Ti ₁ , the amount S is the low-pressure EGR valve 24 is determined to prohibit the low-pressure EGR control when the second determination value De ₂ or more is fully closed. Thus, by performing the prohibition determination in consideration of the intake air temperature Ti, the low pressure EGR valve 24 can be appropriately fully closed in accordance with the operating state of the engine 10, and the generation of condensed water can be effectively performed. Can be suppressed.

  In the control device 1 described above, when the determination unit 2 determines that the low pressure EGR control is permitted, the low pressure EGR control is performed in accordance with the operating state of the engine 10. Gas can be introduced into the intake passage 21.

[5. Others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
The above-described operation map, outside air temperature map, and intake air temperature map are all examples, and are not limited to the above. For example, the operation map is provided as a three-dimensional map using the engine speed Ne, the load Pe, and the intake air temperature Ti as parameters, and a prohibited region (predetermined low-load operation region) is set in the three-dimensional map. May be. In addition, only an operation map in which a prohibited region is set when the intake air temperature Ti is higher than the predetermined temperature Tth and an operation map in which a prohibited region is set when the intake air temperature Ti is lower than the predetermined temperature Tth are set. May be. In other words, the prohibited area does not have to be further expanded to the high load side in accordance with a decrease in the intake air temperature Ti.

In the outside air temperature map, all temperature ranges below the first outside air temperature Ta ₁ may be set in the prohibited range. That is, the first determination value De ₁ is omitted from the outside air temperature map, and if the outside air temperature Ta is equal to or lower than the first outside air temperature Ta ₁ , it is determined that the low pressure EGR control is prohibited and the low pressure EGR valve 24 is fully closed. It may be a configuration. Even in such a configuration, the low pressure EGR valve 24 is appropriately fully closed in an environmental state in which an increase in the amount of condensed water generation or freezing of the condensed water is a concern. can do.

Further, the intake air temperature map may be set such that the low temperature side is set as the prohibited range and the high temperature side is set as the allowable range with the first intake temperature Ti ₁ or the predetermined intake temperature Ti ₀ as the boundary line. Alternatively, the intake air temperature map, as the outside air temperature map shown in FIG. 3, all at a temperature range higher than the predetermined intake air temperature Ti ₀ is set to the allowable range, the predetermined intake air temperature Ti ₀ following temperature range, the second determination The value De ₂ or more may be set as the prohibited range, and the value less than the second determination value De ₂ may be set as the allowable range. Note that the order of determination by the determination unit 2 may not be the above. Further, one or both of the second and third prohibition determinations using the outside air temperature Ta and the intake air temperature Ti may be omitted. Alternatively, the second and third prohibition determinations by the determination unit 2 may be omitted, and the control unit 3 may directly control the low pressure EGR valve 24 using the outside air temperature Ta and the intake air temperature Ti.

  In the above embodiment, the temperature detected by the intake air temperature sensor 38 provided in the intake manifold 19 is used as the intake air temperature Ti, but the intake air temperature Ti is not limited to this. For example, based on information from sensors generally provided in the intake and exhaust systems, create a physical model that takes into account the mixing ratio of the recirculated gas, the efficiency of the turbine, the heat reception in the intake air transportation process, and hardware degradation, The temperatures before and after the intercooler 26 may be estimated and used as a substitute for the intake air temperature Ti. Moreover, in the said embodiment, although the storage amount S of the condensed water is detected by the detection part 39, it replaces with or in addition to this, the operating time of the engine 10, rotation speed Ne, low-pressure recirculation gas amount, A configuration for estimating the storage amount S based on the saturated water vapor amount or the like according to the intake air temperature Ti or the outside air temperature Ta may be provided.

In the above embodiment, the tank 27B in which the condensed water is stored is provided, but the condensed water may be stored in one or both of the separator 27A and the discharge passage 27C. That is, the separator 27A and the discharge passage 27C may each function as a condensed water storage unit.
The configuration of the engine 10 is not limited to the above. For example, an engine without the high pressure EGR passage 35 and the turbocharger 25 may be used, or an engine without the low pressure throttle valve 23 and the high pressure throttle valve 28 may be used. Moreover, it is not restricted to a diesel engine, A gasoline engine may be sufficient.

DESCRIPTION OF SYMBOLS 1 Control apparatus 2 Determination part 3 Control part 10 Engine 21 Intake passage 24 Low pressure EGR valve (EGR valve)
26 Intercooler 27 Separator 27A Separator 27B Tank (Condensate Storage Unit)
31 Exhaust passage 33 Low pressure EGR passage (EGR passage)
Ne rotation speed
Pe load
Pe ₀ Predetermined load value
S Storage volume
Ti intake temperature
Tth Specified temperature
Ti ₁ first intake air temperature
Ta outside temperature
Ta ₁ First outside air temperature
Ta ₂ Second outside air temperature
De ₁ first judgment value
De ₂ second judgment value

Claims (5)

An intercooler for cooling the intake air flowing through the intake passage;
An EGR passage communicating the exhaust passage and the intake passage upstream of the intercooler;
An EGR valve that opens and closes communication of the EGR passage;
A condensate storage section for storing condensate water generated by the intercooler;
A determination unit for determining whether or not the operating state of the engine is within a predetermined low-load operation region;
A controller that fully closes the EGR valve when it is determined that the operating state of the engine is within the predetermined low-load operation region,
When the intake air temperature is higher than a predetermined temperature, the determination unit sets an area where the engine load is equal to or lower than a predetermined load value as the predetermined low load operation area, and when the intake air temperature is equal to or lower than the predetermined temperature. The engine control device extends the predetermined low-load operation region so that the predetermined load value increases as the engine speed increases. The determination unit further expands the predetermined low-load operation region to a higher load side as the intake air temperature is lower than the predetermined temperature when the intake air temperature is equal to or lower than the predetermined temperature. The engine control device according to claim 1. 3. The engine control device according to claim 1, wherein when the outside air temperature is equal to or lower than a predetermined first outside air temperature, the control unit fully closes the EGR valve. 4. The controller is
The outside air temperature is equal to or higher than a second outside air temperature that is equal to or lower than a predetermined first outside air temperature and lower than the first outside air temperature, and the amount of condensate stored in the condensate water storage unit is such that the outside air temperature is the second outside air temperature. When the value is equal to or greater than the first determination value that is set to be smaller, the EGR valve is fully closed,
The engine control apparatus according to claim 1 or 2, wherein the EGR valve is fully closed even when the outside air temperature is lower than the second outside air temperature. The controller is
When the intake air temperature is lower than the first intake air temperature lower than the predetermined temperature, the EGR valve is fully closed,
When the intake air temperature is equal to or higher than the first intake air temperature, the amount of condensed water stored in the condensed water storage portion is equal to or higher than a second determination value that is set higher as the intake air temperature is higher than the first intake air temperature. The engine control device according to any one of claims 1 to 4, wherein if there is, the EGR valve is fully closed.

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