JP2012229655A - Exhaust circulation device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust circulation device of an internal combustion engine capable of controlling the corrosion of an EGR cooler by favorably performing water injection control for the EGR cooler.SOLUTION: An ECU prohibits any water injection (Step S13) when determining that the cooling water temperature Tw is equal to or lower than a predetermined value A (YES in Step S12). On the other hand, the ECU determines whether or not the cooling water temperature Tw exceeds the predetermined value B (Step S14) when determining that the cooling water temperature Tw exceeds the predetermined value A (NO in Step S12). The ECU prohibits the water injection (Step S15) when determining that the cooling water temperature Tw exceeds a predetermined value B (YES in Step S14). On the other hand, an ECU 80 determines that the cooling water temperature Tw is dropping (Step S16) when determining that the cooling water temperature Tw is equal to or lower than the predetermined value B (NO in Step S14), and performs the water injection control (Step S17) when determining that the cooling water temperature Tw is not dropping (NO in Step S16).

Description

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

  Conventionally, in order to reduce the fuel consumption of an internal combustion engine, an exhaust gas circulation device that recirculates gas burned in a combustion chamber as EGR gas to an intake passage has been proposed (for example, see Patent Document 1).

  The exhaust gas circulation device disclosed in Patent Document 1 recirculates a part of the exhaust gas flowing through the exhaust passage to the intake passage and the flow rate of EGR gas provided in the EGR passage and recirculated to the intake passage. An EGR valve to be adjusted, and an EGR cooler which is provided on the exhaust passage side from the EGR valve and cools the recirculated EGR gas by heat exchange with the engine cooling water.

  Such an exhaust circulation device realizes the recirculation of the EGR gas from the exhaust passage to the intake passage according to the operating state of the internal combustion engine by adjusting the flow rate of the EGR gas flowing through the EGR passage by the EGR valve. It has become.

  The EGR gas contains particulate matter such as soot, and when the particulate matter adheres to the EGR cooler, the cooling efficiency of the EGR gas decreases. Further, corrosive components such as chlorine components and sulfur components contained in the fuel are mixed into the EGR gas and introduced into the EGR cooler. At this time, if condensed water is generated in the EGR cooler, these corrosive components are dissolved in the condensed water and become corrosive water. As a result, this corrosive water causes the EGR cooler to corrode.

  Therefore, an exhaust circulation device that cleans the inside of the EGR cooler by injecting water into the EGR cooler is known (see, for example, Patent Document 2).

  The exhaust gas circulation device disclosed in Patent Document 2 includes an injector for water injection on the upstream side of the EGR gas flow of the EGR cooler. Water is injected from the injector during combustion of the engine, and water is mixed into the EGR gas. By doing so, water is supplied into the EGR cooler. As a result, the soot adhering to the EGR cooler is washed away, and when the water is vaporized by the high-temperature EGR gas, the heat of the EGR gas is consumed as the heat of vaporization, so that the EGR gas can be cooled.

JP 2009-228530 A JP 2010-48113 A

  However, the above-described conventional exhaust circulation device does not consider the timing of injecting water from the injector.

  For this reason, when the injector injects water while the engine is not being circulated, the injected water is not blown off from the EGR cooler by the EGR gas and is accumulated in the EGR cooler. Even when the EGR valve is closed due to warm-up, exhaust gas repeatedly enters and leaves the EGR pipe due to exhaust pulsation. As a result, the water accumulated in the EGR cooler has a problem that it corrodes the EGR cooler because the corrosive components contained in the exhaust gas dissolve into the corrosive water.

  Even when the engine is warmed up and the coolant temperature reaches the temperature at which the exhaust circulation control is executed, the wall temperature inside the EGR cooler is insufficient as the temperature for evaporating the water.

  Therefore, during the execution of the exhaust gas circulation control, the water injected from the injector is accumulated in the EGR cooler and the EGR gas, although the wall temperature of the EGR cooler is higher than the dew point and no condensed water is originally generated. There is a possibility that corrosive components contained in the water may be mixed to become corrosive water, resulting in a problem that the EGR cooler is corroded.

  That is, the water injection control for the EGR cooler is not suitably executed, and there is a problem that the corrosion of the EGR cooler cannot be sufficiently suppressed.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide an exhaust circulation device for an internal combustion engine that can suitably execute water injection control on the EGR cooler and suppress corrosion of the EGR cooler. .

  An exhaust gas circulation device for an internal combustion engine according to the present invention is an exhaust gas circulation device for an internal combustion engine that circulates a part of the exhaust gas discharged from the internal combustion engine to the exhaust passage as EGR gas to the intake passage to achieve the above-described object, An EGR valve installed in an EGR passage communicating the exhaust passage and the intake passage, and taking at least a closed state capable of interrupting the circulation of the EGR gas and an open state enabling the circulation of the EGR gas; and the EGR An EGR cooler that is installed in a passage and cools the EGR gas; an injector that is installed in the EGR cooler and injects water into the EGR cooler; and a control unit that controls injection of water by the injector, The control means is conditioned on the condition that the EGR valve is closed and the cooling water temperature of the internal combustion engine is not more than a predetermined value. And inhibits the injection of water by connectors.

  With this configuration, when the cooling water temperature is equal to or lower than the predetermined value and there is a high possibility that the water injected into the EGR cooler is accumulated in the EGR cooler, the water is accumulated in the EGR cooler by prohibiting the water injection. It can suppress that it becomes corrosive water when the corrosive component contained in EGR gas melt | dissolves in this water. Therefore, it can suppress that an EGR cooler corrodes with corrosive water.

  In the exhaust gas recirculation apparatus for an internal combustion engine according to the present invention, the control means starts water injection by the injector on condition that the cooling water temperature exceeds the predetermined value.

  With this configuration, the water injected from the injector is blown off by the EGR gas when the exhaust gas recirculation amount control is executed, so that it is possible to suppress water from being accumulated in the EGR cooler. Further, when the cooling water temperature exceeds a predetermined value, there is a possibility that the corrosive water generated during the warm-up already exists in the EGR cooler. Therefore, if the internal combustion engine is stopped before the exhaust gas recirculation control is started, the corrosive water remains in the EGR cooler. However, since the concentration of the corrosive water is diluted by the injected water, the EGR cooler Corrosion can be suppressed.

  Further, in the exhaust gas recirculation device for an internal combustion engine according to the present invention, the control means is another predetermined value in which the EGR valve is open and the cooling water temperature is set to a higher temperature side than the predetermined value. The injection of water by the injector is prohibited on the condition that the above is exceeded.

  With this configuration, when the condition that no condensed water is generated in the EGR cooler is established, water injection by the injector can be prohibited. Therefore, it is possible to prevent the possibility that water is accumulated in the EGR cooler by continuing the water injection despite the fact that condensed water cannot be generated.

  In the exhaust gas circulation device for an internal combustion engine according to the present invention, the control means prohibits water injection by the injector on condition that the internal combustion engine is stopped.

  With this configuration, even when the cooling water temperature falls between a predetermined value and another predetermined value due to a decrease in the cooling water temperature due to the stop of the internal combustion engine, water injection by the injector is prohibited. Accordingly, it is possible to prevent water from accumulating in the EGR cooler by injecting water by the injector even though condensed water is not generated in the EGR cooler.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust-air-circulation apparatus of the internal combustion engine which can perform suitably the water injection control with respect to an EGR cooler, and can suppress corrosion of an EGR cooler can be provided.

1 is a schematic configuration diagram illustrating an exhaust gas circulation device for an internal combustion engine according to an embodiment of the present invention. It is a schematic block diagram which shows the structure of the exhaust-gas circulation apparatus which concerns on embodiment of this invention, and its periphery. It is a schematic block diagram which shows the structure of the cooling water circuit which concerns on embodiment of this invention. It is a schematic structure figure showing the inside of the EGR cooler concerning an embodiment of the invention. It is a flowchart for demonstrating the water-injection control which concerns on embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, a case will be described in which the exhaust gas circulation device according to the present invention is applied to a vehicle equipped with a 4-cylinder gasoline engine.

  First, the configuration will be described.

  As shown in FIG. 1, the engine 1 includes a cylinder head 10 and a cylinder block (not shown). The cylinder head 10 and the cylinder block form four cylinders 5. In these cylinders 5, combustion chambers 7 are respectively defined by pistons. The cylinder head 10 is formed with an intake port for introducing outside air into the cylinder 5 and an exhaust port for discharging exhaust gas from the cylinder 5.

  Each intake port is provided with an injector for fuel injection. The injected fuel is mixed with air and introduced into the combustion chamber 7 as an air-fuel mixture. Further, the cylinder head 10 includes an intake valve that switches a communication state between the intake port and the combustion chamber 7 at every predetermined rotation angle of the intake camshaft, and an exhaust port and the combustion chamber 7 at every predetermined rotation angle of the exhaust camshaft. An exhaust valve is installed to switch the communication state with the.

  The cylinder head 10 is provided with an ignition plug 15 for igniting the air-fuel mixture introduced into each combustion chamber 7. The ignition plug 15 controls ignition timing by an ECU (Electronic Control Unit) 80 described later. It has come to be.

  The fuel injection injector is constituted by an electromagnetically driven on / off valve. When a predetermined voltage is applied by the ECU 80, the fuel injection injector is opened to inject fuel into the intake port of each cylinder 5.

  The engine 1 further has an intake manifold 11 a connected to the cylinder head 10, and the intake manifold 11 a constitutes a part of the intake passage 11. The intake passage 11 is provided with an air cleaner and an air flow meter 22 (not shown) in order from the upstream side. The intake passage 11 is further provided with a throttle valve 18 for adjusting the intake air amount on the upstream side of the intake manifold 11a.

  The throttle valve 18 is constituted by an electronically controlled on-off valve whose opening degree can be adjusted steplessly. The flow area of the intake air is reduced under a predetermined condition, and the supply amount of the intake air is reduced. To be adjusted. The ECU 80 controls the throttle motor installed in the throttle valve 18 to adjust the opening degree of the throttle valve 18.

  The engine 1 further has an exhaust manifold 12 a connected to the cylinder head 10, and the exhaust manifold 12 a constitutes a part of the exhaust passage 12. In the exhaust passage 12, a catalyst device 13 made of, for example, a three-way catalyst is disposed.

  The engine 1 further includes an exhaust circulation device (hereinafter referred to as an EGR device) 30. The EGR device 30 recirculates a part of the exhaust gas flowing through the exhaust passage 12 to the intake passage 11 and supplies it to the combustion chamber 7 of each cylinder 5 as EGR gas. Thereby, the combustion temperature in the combustion chamber 7 falls, and NOx generation amount reduces. In addition, the pumping loss is reduced and the fuel consumption is improved.

  The EGR device 30 includes an EGR pipe 33 in which an intake pipe 14 that forms the intake passage 11 and an exhaust pipe 16 that forms the exhaust passage 12 are connected and an EGR passage 34 is formed inside. The EGR pipe 33 is provided with an EGR cooler 31 and an EGR valve 32 for cooling the EGR gas flowing through the EGR passage 34 in order from the upstream side of the EGR gas flow.

  The EGR valve 32 is provided with a linear solenoid 32a provided therein and a base end portion inserted through the linear solenoid 32a, and a valve body 32b for opening and closing the EGR passage 34 is provided at the tip portion thereof. And a shaft 32c. By controlling energization of the linear solenoid 32a, the shaft 32c is reciprocated in the axial direction by the electromagnetic force and the biasing force of a spring (not shown), and the EGR passage 34 is opened and closed by the valve body 32b.

  The EGR valve 32 in the present embodiment is a normally closed type valve that is opened when the linear solenoid 32a is energized and closed when the linear solenoid 32a is not energized.

  The ECU 80 adjusts the amount of EGR gas introduced into the intake manifold 11a through the exhaust passage 12 and the intake passage 11 by adjusting the opening of the EGR valve 32, that is, the exhaust gas recirculation amount.

  The EGR cooler 31 has a configuration in which a refrigerant chamber 62 (see FIG. 4) is stretched around the outer periphery of the EGR gas passage in the housing. The EGR gas supplied from the EGR pipe 33 is cooled by heat exchange with the cooling water flowing through the refrigerant chamber 62 when passing through the EGR gas passage, and is guided downstream. In addition, the EGR cooler 31 according to the present embodiment has a water injection injector 35 as described later.

  As shown in FIGS. 1 and 2, a vehicle equipped with the engine 1 according to the present embodiment includes a cooling water temperature sensor 21, an air flow meter 22, an intake air temperature sensor 23, a pressure sensor 24, an exhaust cam angle sensor 25, an exhaust temperature. A sensor 26, a throttle opening sensor 27, an accelerator opening sensor 29, a lift sensor 36, an engine speed sensor 37, an outside air temperature sensor 55, and a humidity sensor 56 are provided. Each of these sensors outputs a signal representing a detection result to the ECU 80.

  The coolant temperature sensor 21 is disposed in a water jacket formed in the cylinder block of the engine 1, and outputs a detection signal corresponding to the coolant temperature Tw of the engine 1 to the ECU 80. The air flow meter 22 is arranged upstream of the throttle valve 18 in the intake passage 11 and outputs a detection signal corresponding to the intake air amount to the ECU 80.

  The intake air temperature sensor 23 is disposed in the intake manifold 11a, and outputs a detection signal corresponding to the intake air temperature to the ECU 80. The pressure sensor 24 is disposed in the intake manifold 11a, and outputs a detection signal corresponding to the intake pressure to the ECU 80.

  The exhaust cam angle sensor 25 detects a predetermined position of the exhaust cam sensor plate provided on the exhaust cam shaft, that is, a predetermined rotation angle, and detects the rotation angle of the exhaust cam shaft. The exhaust temperature sensor 26 is disposed in the exhaust passage 12 on the downstream side of the catalyst device 13, and outputs a detection signal corresponding to the exhaust temperature to the ECU 80.

  The throttle opening sensor 27 outputs a detection signal corresponding to the opening of the throttle valve 18 to the ECU 80. The accelerator opening sensor 29 outputs a detection signal corresponding to the depression amount of the accelerator pedal to the ECU 80. The engine rotation speed sensor 37 detects the rotation speed of the crankshaft of the engine 1 and outputs it to the ECU 80 as the engine rotation speed.

  The lift sensor 36 has a resistor that is DC driven and a brush that slides on the surface of the resistor. The brush is configured to operate integrally with the shaft 32c of the EGR valve 32. A voltage signal corresponding to the lift position of the shaft 32c, that is, the opening degree of the EGR valve 32 appears on the brush. Therefore, the ECU 80 can detect the opening degree of the EGR valve 32 by acquiring a signal appearing on the brush of the lift sensor 36. The outside air temperature sensor 55 and the humidity sensor 56 detect the temperature and humidity of the outside air of the vehicle, respectively, and output them to the ECU 80.

  As shown in FIG. 2, the ECU 80 includes a CPU (Central Processing Unit) 81, a ROM (Read Only Memory) 82, a RAM (Random Access Memory) 83, a backup memory 84, and the like. Note that the ECU 80 according to the present embodiment constitutes a control means according to the present invention.

  The ROM 82 stores various control programs including a control program for controlling the exhaust gas recirculation amount control, the water injection control, and the fuel injection amount for the cylinder 5, maps that are referred to when executing these various control programs, and the like. ing. The CPU 81 executes various arithmetic processes based on various control programs and maps stored in the ROM 82. In addition, the RAM 83 temporarily stores calculation results by the CPU 81, data input from the above-described sensors, and the like. The backup memory 84 is configured by a non-volatile memory, and stores, for example, data to be saved when the engine 1 is stopped.

  The CPU 81, ROM 82, RAM 83, and backup memory 84 are connected to each other via a bus 87 and are connected to an input interface 85 and an output interface 86.

  The input interface 85 includes a coolant temperature sensor 21, an air flow meter 22, an intake air temperature sensor 23, a pressure sensor 24, an exhaust cam angle sensor 25, an exhaust temperature sensor 26, a throttle opening sensor 27, an accelerator opening sensor 29, and a lift sensor 36. The engine speed sensor 37, the outside air temperature sensor 55, and the humidity sensor 56 are connected. The vehicle may be mounted with an ECU other than the ECU 80, and signals output from at least some of these sensors may be input to the ECU 80 via the other ECU.

  The output interface 86 is connected to the spark plug 15, the throttle valve 18, the EGR valve 32, the water injection injector 35, the fuel injection injector, and the like. Then, the ECU 80 executes various controls of the engine 1 including exhaust gas recirculation amount control, water injection control, fuel injection amount control, and the like based on the outputs of the various sensors described above.

  FIG. 3 is a schematic diagram showing a cooling water circuit 40 that supplies cooling water to the EGR device 30 according to the present embodiment. The cooling water circuit 40 supplies the cooling water discharged from the water pump 44 in the order of the engine 1, the heater core 41, the EGR cooler 31, the EGR valve 32, and the throttle valve 18, and returns to the water pump 44. A second part of the cooling water branched from the first path 47 by a thermostat (not shown) installed downstream of the cylinder head 10 constituting the engine 1 and supplied from the engine 1 to the radiator 42 and returned to the water pump 44 Path 48.

  When the cooling water flowing back through the first path 47 is heated by heat exchange with the cylinder block and the cylinder head 10 constituting the engine 1, it is cooled by heat exchange with the heater core 41 and then supplied to the EGR cooler 31. .

  On the other hand, when the cooling water flowing back through the second path 48 is branched from the first path 47 by a thermostat installed downstream of the cylinder head 10, it is supplied to the radiator 42 and cooled by heat exchange with the outside air. Further, as the cooling water temperature Tw rises, the thermostat gradually opens the second path 48 so that the ratio of the cooling water amount returning through the second path 48 to the cooling water amount returning through the first path 47 increases. It has become.

  Hereinafter, a more characteristic configuration of the EGR device 30 according to the embodiment of the present invention will be described with reference to FIGS. 1 and 4.

  The EGR cooler 31 according to the present embodiment is provided with a water injection injector 35 for injecting water into the EGR cooler 31.

  Further, the vehicle is provided with a water tank 51, and the water in the water tank 51 is sucked up by the pump 52 through the filter 53 and supplied to the water injection injector 35.

  The pump 52 is configured by a known electric pump, but may be configured by a mechanical pump or the like. The water should just be a liquid which can wash | clean corrosive water, such as distilled water, for example.

  The water injection injector 35 has a needle as an injection valve and a solenoid that displaces the needle in the axial direction by a predetermined lift amount. Therefore, the ECU 80 adjusts the amount of water injected from the water injection injector 35 by controlling the energization time for the solenoid.

  As shown in FIG. 4, the interior of the EGR cooler 31 is a partition plate provided so that a casing 61 into which EGR gas is guided and a refrigerant chamber 62 in which cooling water as a refrigerant flows in the casing 61 are formed. 63 and a plurality of cooling pipes 64 arranged so as to penetrate the refrigerant chamber 62 and through which the EGR gas passes. The cooling pipe 64 is arranged in one direction in the casing 61. The cooling pipes 64 are arranged such that the upstream end 64a and the downstream end 64b are aligned on the same plane. Fins 65 are provided in the cooling pipe 64 so as to promote the transfer of heat from the EGR gas to the cooling water. The EGR gas is introduced into the casing 61 through the inlet 61a. Thereafter, the EGR gas passes through the plurality of cooling pipes 64 and is discharged from the discharge ports 61b.

  A coolant introduction port 62a is formed in the refrigerant chamber 62, and the coolant that has passed through the heater core 41 (see FIG. 3) is introduced through the coolant introduction port 62a. The cooling water passes between the plurality of cooling pipes 64 and is discharged from the cooling water discharge port 62b, and is supplied to the EGR valve 32 (see FIG. 3). By flowing the cooling water in this way, the EGR gas can be cooled by causing heat exchange between the EGR gas passing through the plurality of cooling pipes 64 and the cooling water.

  In the EGR cooler 31 according to the present embodiment, the water injection injector 35 is installed in the casing 61 on the upstream side of the upstream end portion 64a. The water injection injector 35 injects water toward the fins 65 of the cooling pipes 64 to wash away corrosive water adhering to the cooling pipes 64 including the fins 65.

  Returning to FIG. 1, when the ECU 80 determines that the cooling water temperature Tw is equal to or lower than the predetermined value A based on the signal input from the cooling water temperature sensor 21, the water injection by the water injection injector 35 is prohibited. Yes. Here, the predetermined value A according to the present embodiment constitutes the predetermined value according to the present invention. This predetermined value A is set in the vicinity of 55 ° C., which is the dew point temperature of EGR gas.

  When the cooling water temperature Tw is equal to or lower than the predetermined value A, once condensed water is generated in the EGR cooler 31, the exhaust gas recirculation amount control is not executed, so that it is not blown off or dried by the EGR gas. Therefore, when water is injected into the EGR cooler 31 by the water injection injector 35, the water is accumulated in the EGR cooler 31. When the cooling water temperature Tw is equal to or lower than the predetermined value A, the exhaust gas recirculation amount control has not started yet, and the EGR valve 32 is in the fully closed state, but the exhaust passage 12 generated by driving the engine 1 Due to the exhaust pulsation, the exhaust gas repeatedly flows into and out of the EGR passage 34 and gradually enters the EGR cooler 31. As a result, the water accumulated in the EGR cooler 31 dissolves into corrosive components contained in the exhaust gas and becomes corrosive water, which causes the EGR cooler 31 to corrode. Therefore, when the cooling water temperature Tw is equal to or lower than the predetermined value A, the ECU 80 prohibits water injection by the water injection injector 35 and prevents water that causes corrosive water from accumulating in the EGR cooler 31. It has become.

  Here, the predetermined value A is a temperature at which condensed water is not generated in the EGR cooler 31, that is, a temperature near the dew point temperature of the EGR gas and higher than the dew point temperature, and a temperature at which exhaust gas recirculation control is executed. It is set at a lower temperature and may be either a constant value or a fluctuation value. When the predetermined value A is a constant value, the predetermined value A is set based on the highest dew point of the exhaust gas based on the assumed outside air temperature and humidity.

  On the other hand, when the predetermined value A is set as the fluctuation value, the ECU 80 calculates the predetermined value A according to the outside air temperature and humidity. In this case, the ECU 80 stores a calculation formula for calculating the predetermined value A from the outside air temperature and humidity in the ROM 82 in advance. When the ECU 80 acquires signals representing the outside air temperature and humidity from the outside air temperature sensor 55 and the humidity sensor 56, the ECU 80 calculates a predetermined value A based on a calculation formula stored in the ROM 82.

  Alternatively, the ECU 80 stores a map in which the outside air temperature and humidity are associated with the predetermined value A in advance in the ROM 82, and acquires a signal representing the outside air temperature and humidity from the outside air temperature sensor 55 and the humidity sensor 56, and then stores the map in the ROM 82. The predetermined value A is calculated with reference to the stored map.

  In the present embodiment, the ECU 80 calculates the predetermined value A only when the engine 1 is started. However, the present invention is not limited to this. The predetermined value A may be calculated for each time interval, and the predetermined value A that has already been set may be updated with a newly calculated value.

  When the ECU 80 determines that the cooling water temperature Tw has exceeded the predetermined value A based on the signal input from the cooling water temperature sensor 21, the ECU 80 starts water injection by the water injection injector 35. .

  When the cooling water temperature Tw exceeds the predetermined value A, the condensed water generated when the EGR cooler 31 is at or below the dew point temperature has already accumulated in the EGR cooler 31, and corrosive components are generated by the exhaust pulsation described above. It is dissolved and corrosive water. Therefore, the ECU 80 can reduce the concentration of the corrosive water already accumulated in the EGR cooler 31 by injecting water into the EGR cooler 31.

  Further, when the engine 1 is stopped in this state and the cooling water temperature Tw starts to decrease, the condensed water generated in the EGR cooler 31 does not evaporate and is before the execution of the exhaust gas recirculation amount control. Therefore, it is not blown away by the EGR gas. Therefore, it remains as corrosive water in the EGR cooler 31. However, since the ECU 80 has already performed water injection when the cooling water temperature Tw exceeds the predetermined value A, the concentration of the corrosive water is reduced as compared with the case where the water injection is not performed, and the EGR cooler 31 Corrosion of the steel is suppressed.

  When the cooling water temperature Tw reaches the execution temperature of the exhaust gas recirculation amount control, the ECU 80 starts the exhaust gas recirculation amount control for controlling the opening degree of the EGR valve 32.

  Here, the execution start temperature of the exhaust gas recirculation amount control is set to 70 ° C., for example. Accordingly, when the ECU 80 determines that the cooling water temperature Tw has reached 70 ° C. based on the signal input from the cooling water temperature sensor 21, the ECU 80 starts executing the exhaust gas recirculation amount control, while the water injection by the water injection injector 35 is performed. continue. Therefore, the water injected into the EGR cooler 31 is blown off by the EGR gas, discharged from the EGR cooler 31, flows into the engine 1 together with the EGR gas, and is discharged outside the vehicle together with the exhaust gas. .

  Further, in the water injection control, the ECU 80 controls the water injection injector 35 to intermittently inject water so as to wash the condensed water generated in the EGR cooler 31 with a minimum injection amount. It has become.

  Specifically, the water injected into the EGR cooler 31 is more easily blown from the EGR cooler 31 as the flow rate of the EGR gas is larger. Further, the flow rate of EGR gas to the EGR cooler 31 is greatly affected by exhaust pulsation. For this reason, the ECU 80 controls the water injection injector 35 in synchronization with the opening / closing timing of the exhaust valve, whereby water injection is executed in a state where the flow rate of the EGR gas to the EGR cooler 31 is large. In this case, the ECU 80 controls the water injection injector 35 based on the signal input from the exhaust cam angle sensor 25 so that water is injected at the respective opening timings of the exhaust valves arranged in the respective cylinders. To do.

  On the other hand, if the EGR gas flow rate increases due to the high engine speed and the engine load factor and the EGR valve 32 being in the fully open state and its vicinity, the fluctuation in the EGR gas flow rate is greater than the opening / closing timing of the exhaust valve. It is strongly influenced by the opening / closing timing of the intake valve. Therefore, the ECU 80 may synchronize the control of the water injection injector 35 with the opening / closing timing of the intake valve in a traveling state of the vehicle in which the flow rate of EGR gas is greater than a predetermined value. In this case, the ECU 80 determines whether the water injection injector 35 is synchronized with the opening / closing timing of the intake valve or the exhaust valve based on a map set in accordance with the engine speed and the engine load factor. This map is set by experimental measurement and is stored in the ROM 82 in advance. When executing the water injection control in synchronization with the intake valve, the ECU 80 controls the water injection injector 35 so that water is injected at each opening timing of the intake valve disposed in each cylinder. To.

  The ECU 80 may control the injection amount at each injection timing of the water injection injector 35. In this case, as described above, the water injected into the EGR cooler 31 is more easily blown away from the EGR cooler 31 as the flow rate of the EGR gas is larger. Therefore, the ECU 80 increases the injection amount as the flow rate of the EGR gas increases, so that the EGR gas and water have a certain ratio. For example, the ECU 80 calculates the flow rate of the EGR gas based on the intake air amount 22 detected by the air flow meter 22 and the EGR rate. Then, the ECU 80 controls the water injection injector 35 so that the injection amount corresponds to the calculated flow rate of the EGR gas.

  Further, when the coolant temperature Tw exceeds a predetermined value B, the ECU 80 prohibits water injection by the water injection injector 35. Here, the predetermined value B according to the present embodiment constitutes another predetermined value according to the present invention, in which condensed water cannot be generated in the EGR cooler 31, and exhaust gas recirculation amount control is executed. It is set in the vicinity of 75 ° C., which is the temperature to be heated.

  The inner wall temperature of the EGR cooler 31 substantially matches the cooling water temperature Tw. Therefore, if the cooling water temperature Tw exceeds 75 ° C., the inner wall temperature of the EGR cooler 31 is sufficiently higher than the dew point temperature of the EGR gas, and condensed water cannot be newly generated in the EGR cooler 31. However, since the cooling water temperature Tw after the engine 1 is warmed up is usually in the range of 75 ° C. to 100 ° C., if the water injection is continued under this condition, the water is sufficiently evaporated in the EGR cooler 31. There is a possibility that water will accumulate. In this state, since the exhaust gas recirculation amount control is executed, the accumulated water is constantly exposed to the EGR gas. Therefore, the corrosive component contained in the EGR gas dissolves in the accumulated water, and the accumulated water corrodes the EGR cooler 31 as corrosive water. Furthermore, the humidity in the EGR cooler 31 increases due to evaporation of a part of the accumulated water, which may further promote corrosion in the EGR cooler 31. Therefore, the ECU 80 prohibits water injection by the water injection injector 35 when the cooling water temperature Tw exceeds 75 ° C.

  Moreover, once the cooling water temperature Tw becomes 75 ° C. or higher and water injection is prohibited, the EGR cooler 31 is in a dry state as described above. Therefore, even if the cooling water temperature Tw is 75 ° C. or higher, such as when the engine 1 is stopped, even if it falls between 55 ° C. and 75 ° C., that is, between the predetermined value A and the predetermined value B, condensed water is contained in the EGR cooler 31. There is no accumulation of water. In spite of such a dry state, when water injection is performed, water is accumulated in the EGR cooler 31 and causes the EGR cooler 31 to corrode as corrosive water.

  Therefore, when the cooling water temperature Tw is lowered and is between the predetermined value A and the predetermined value B because the engine 1 is stopped, the ECU 80 does not generate condensed water in the EGR cooler 31. Water injection by the water injection injector 35 is prohibited.

  In this case, when the ECU 80 determines that the engine 1 is stopped based on a signal input from the engine speed sensor 37, the water injection by the water injection injector 35 may be prohibited. . Alternatively, the ECU 80 calculates the time change of the cooling water temperature Tw based on the signal input from the cooling water temperature sensor 21, and when it is determined that the cooling water temperature Tw is decreasing, the water injection by the water injection injector 35 is performed. May be prohibited.

  In addition, the ECU 80 has a water injection prohibition flag in the RAM 83 that indicates whether or not to prohibit water injection control. The ECU 80 sets the water injection prohibition flag to ON when the coolant temperature Tw is equal to or lower than the predetermined value A as described above, when the coolant temperature Tw exceeds the predetermined value B, or when the engine 1 is stopped. In other cases, the water injection prohibition flag is set to OFF. The ECU 80 executes water injection control when the water injection prohibition flag is OFF, and prohibits water injection control when it is ON. The water injection prohibition flag may be stored in the backup memory 84 instead of the RAM 82.

  Next, water injection control processing according to the present embodiment will be described with reference to FIG. Note that the following processing is executed at a predetermined timing by the CPU 81 constituting the ECU 80 and implements a program that can be processed by the CPU 81.

  As shown in FIG. 5, the ECU 80 first acquires the coolant temperature Tw of the engine 1 based on the signal input from the coolant temperature sensor 21 (step S11).

  Next, the ECU 80 determines whether or not the coolant temperature Tw is equal to or lower than a predetermined value A (step S12). Specifically, when the ECU 80 acquires a signal representing the current outside air temperature and humidity based on signals input from the outside air temperature sensor 55 and the humidity sensor 56, the ECU 80 performs predetermined processing based on a calculation formula stored in the ROM 82. Set the value A. As described above, the predetermined value A is set near the dew point temperature.

  When the ECU 80 determines that the coolant temperature Tw is equal to or lower than the predetermined value A (YES in step S12), the ECU 80 turns on the water injection prohibition flag stored in the RAM 83 and prohibits water injection (step S13). Further, as described above, the exhaust gas recirculation amount control is started when the cooling water temperature Tw falls between the predetermined value A and the predetermined value B. Therefore, if the cooling water temperature Tw is equal to or lower than the predetermined value A, EGR The valve 32 is closed.

  On the other hand, when ECU 80 determines that cooling water temperature Tw exceeds predetermined value A (NO in step S12), ECU 80 determines whether cooling water temperature Tw exceeds predetermined value B (step S14). The predetermined value B is a temperature at which condensed water is not reliably generated in the EGR cooler 31 as described above, and is set to 75 ° C. in the present embodiment.

  If the ECU 80 determines that the coolant temperature Tw exceeds the predetermined value B (YES in step S14), the ECU 80 turns on the water injection prohibition flag stored in the RAM 83 and prohibits water injection (step S15). .

  On the other hand, when the ECU 80 determines that the cooling water temperature Tw is equal to or lower than the predetermined value B (NO in step S14), the ECU 80 proceeds to step S16 and determines whether or not the cooling water temperature Tw is decreasing (step). S16).

  Specifically, the ECU 80 inputs a signal representing the engine speed from the engine speed sensor 37. As a result, when the engine speed is equal to or higher than the predetermined value, it is determined that the engine 1 is being driven and the coolant temperature Tw has not decreased. Here, the predetermined value is set to a rotational speed that can be taken when the engine 1 is driven, such as an idle rotational speed. On the other hand, when the engine speed is less than the predetermined value, it is determined that the coolant temperature Tw is decreasing.

  If ECU 80 determines that cooling water temperature Tw is decreasing (YES in step S16), it sets the water injection prohibition flag to ON and prohibits water injection (step S18).

  On the other hand, when ECU 80 determines that cooling water temperature Tw has not decreased (NO in step S16), ECU 80 turns off the water injection prohibition flag stored in RAM 83. Therefore, the ECU 80 executes the water injection control because the water injection prohibition flag is OFF when the water injection prohibition flag is referred to (step S17).

  As described above, the EGR device 30 according to the embodiment of the present invention has a case where the cooling water temperature Tw is equal to or lower than the predetermined value A and there is a high possibility that the water injected into the EGR cooler 31 is accumulated in the EGR cooler 31. By inhibiting the injection of water, it is possible to prevent water from accumulating in the EGR cooler 31 and the corrosive components contained in the EGR gas from being dissolved in the water to become corrosive water. Therefore, it can suppress that EGR cooler 31 corrodes with corrosive water.

  Further, the water injected from the water injection injector 35 after the cooling water temperature Tw exceeds the predetermined value A is blown away by the EGR gas when the exhaust gas recirculation amount control is executed, so that the water is accumulated in the EGR cooler 31. Can be suppressed. Further, when the cooling water temperature Tw exceeds the predetermined value A, there is a possibility that the corrosive water generated during the warming-up already exists in the EGR cooler 31. Therefore, if the engine 1 is stopped before the exhaust gas recirculation control is started, the corrosive water remains in the EGR cooler 31, but the concentration of the corrosive water is diluted by the injected water, so the EGR cooler 31 corrosion can be suppressed.

  Further, when the cooling water temperature Tw exceeds the predetermined value B and the condition that no condensed water is generated in the EGR cooler 31 is established, the water injection by the water injection injector 35 can be prohibited. Therefore, it is possible to prevent the possibility that water is accumulated in the EGR cooler 31 by continuing the water injection despite the fact that condensed water cannot be generated.

  In addition, even when the cooling water temperature Tw falls between the predetermined value A and the predetermined value B due to a decrease in the cooling water temperature Tw due to the stop of the engine 1, water injection by the water injection injector 35 is prohibited. Therefore, water can be prevented from accumulating in the EGR cooler 31 by executing the water injection by the water injection injector 35 even though condensed water is not generated in the EGR cooler 31.

  In the above description, the case where the vehicle is equipped with the water tank 51 and the water in the water tank 51 is supplied to the water injection injector 35 by the pump 52 is not limited to this. The cooling water may be injected from the water injection injector 35. In this case, since the cooling water of the engine 1 is increased to a predetermined water pressure by the water pump 44, it becomes possible to inject water from the water injection injector 35 without installing a new pump.

  In the above description, the ECU 80 has been described for controlling the water injection injector 35 in synchronization with the exhaust valve or the intake valve. However, the ECU 80 may control the water injection injector 35 so that water is injected at an arbitrary time interval or continuously as long as the injected water is sufficiently discharged from the EGR cooler 31.

  In the above description, the case where the EGR device 30 is applied to the engine 1 that does not include the turbo unit has been described. However, the present invention is not limited thereto, and the EGR device 30 may be applied to the engine 1 that includes the turbo unit. Good.

  In this case, the EGR device 30 may constitute a so-called HPL (High-Pressure Loop) that acquires exhaust gas from the upstream side of the turbine wheel and recirculates it as EGR gas to the downstream side of the compressor wheel. Further, the EGR device 30 may constitute an LPL (Low-Pressure Loop) that acquires exhaust gas from the downstream side of the turbine wheel and recirculates it as EGR gas to the upstream side of the compressor wheel.

  Moreover, although the EGR apparatus 30 demonstrated the case where it applied to the vehicle carrying the engine 1 comprised by the gasoline engine, it is not limited to this, The EGR apparatus 30 mounts well-known internal combustion engines, such as a diesel engine. It may be applied to the vehicle.

  In the above description, the case where the EGR device 30 is applied to a port injection engine in which fuel is injected into the intake port has been described. However, the present invention is not limited to this, and fuel is directly injected into each combustion chamber 7. The EGR device 30 may be applied to an in-cylinder injection engine. Further, the EGR device 30 may be applied to an engine in which both in-cylinder injection and port injection are performed.

  The EGR device 30 may be applied not only to a vehicle that uses only the engine 1 as a power source, but also to a hybrid vehicle that uses the engine 1 and a rotating electrical machine as power sources. In this case, since the hybrid vehicle repeatedly starts and stops the engine 1, the frequency of the wall temperature of the EGR cooler 31 rising and falling across the dew point temperature of the EGR gas increases, and as a result, corrosive water is generated in the EGR cooler 31. The possibility of being increased. However, by applying the EGR device 30 according to the present embodiment, the corrosive water can be washed and the corrosion of the EGR cooler 31 can be suppressed.

  As described above, the exhaust gas circulation device according to the present invention is advantageous in that the water injection control for the EGR cooler 31 can be suitably executed to suppress the corrosion of the EGR cooler 31, and is useful for the exhaust gas circulation device of the internal combustion engine. It is.

DESCRIPTION OF SYMBOLS 1 Engine 7 Combustion chamber 11 Intake passage 11a Intake manifold 12 Exhaust passage 12a Exhaust manifold 18 Throttle valve 21 Cooling water temperature sensor 22 Air flow meter 23 Intake temperature sensor 25 Exhaust cam angle sensor 26 Exhaust temperature sensor 27 Throttle opening sensor 30 EGR device 31 EGR Cooler 32 EGR valve 33 EGR pipe 34 EGR passage 35 Water injection injector 37 Engine speed sensor 40 Cooling water circuit 47 First path 51 Water tank 52 Pump 53 Filter 55 Outside air temperature sensor 56 Humidity sensor 64 Cooling pipe 80 ECU

Claims (4)

An exhaust gas circulation device for an internal combustion engine that circulates a part of the exhaust gas discharged from the internal combustion engine into an exhaust passage as EGR gas in the intake passage,
An EGR valve installed in an EGR passage communicating the exhaust passage and the intake passage, and taking at least a closed state in which the circulation of the EGR gas can be interrupted and an open state in which the circulation of the EGR gas can be performed;
An EGR cooler installed in the EGR passage for cooling the EGR gas;
An injector installed in the EGR cooler and injecting water into the EGR cooler;
Control means for controlling the injection of water by the injector,
The control means prohibits the injection of water by the injector on the condition that the EGR valve is in a closed state and a cooling water temperature of the internal combustion engine is not more than a predetermined value. Exhaust circulation device.   2. The exhaust gas recirculation apparatus for an internal combustion engine according to claim 1, wherein the control unit starts water injection by the injector on the condition that the cooling water temperature exceeds the predetermined value.   The control means is configured to inject water by the injector on the condition that the EGR valve is in an open state and the cooling water temperature exceeds another predetermined value set higher than the predetermined value. 3. The exhaust gas recirculation device for an internal combustion engine according to claim 1 or 2, wherein   The internal combustion engine according to any one of claims 1 to 3, wherein the control means prohibits injection of water by the injector on condition that the internal combustion engine is stopped. Engine exhaust circulation system.

Images