JP4687482B2 - Exhaust gas recirculation device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine that introduces part of the exhaust gas of the internal combustion engine into an intake system.

  2. Description of the Related Art An exhaust gas recirculation device for an internal combustion engine is known in which a heat exchanger using cooling water as a refrigerant is provided in an exhaust gas recirculation passage and gas extracted from an exhaust system (exhaust gas recirculation gas) is passed through the heat exchanger. In the case of an exhaust gas recirculation apparatus equipped with a heat exchanger, moisture in the exhaust gas is converted into condensed water by being cooled by the heat exchanger, and the condensed water is generated in the exhaust gas recirculation passage. Such an exhaust gas recirculation device is provided with an exhaust gas recirculation control valve that can adjust the opening degree of the exhaust gas recirculation passage from the fully closed position to the fully open position in order to adjust the amount of the exhaust gas recirculation gas introduced into the intake system. The opening degree of the exhaust gas recirculation control valve is appropriately controlled according to the operating state of the internal combustion engine.

  As a technique for reducing the condensed water generated in the exhaust gas recirculation passage, there is a technique in which a high-temperature exhaust gas recirculation gas is supplied to a position where the condensed water flows down and the condensed water is evaporated using the heat of the gas (Patent Document 1). ). In addition, Patent Documents 2 and 3 exist as prior art documents related to the present invention.

JP-A-9-088728 JP-T-2004-519578 JP 2003-201829 A

  When the amount of condensed water exceeds the allowable limit and the exhaust gas recirculation passage is throttled by the exhaust gas recirculation control valve, the pressure in the exhaust gas recirculation passage rises, and the condensed water is moved outside the exhaust gas recirculation passage by the pressure. There is a risk of leakage. Each of the above documents does not operate the opening degree of the exhaust gas recirculation control valve in relation to the amount of condensed water generated, so the exhaust gas recirculation passage is controlled to perform exhaust gas recirculation when the amount of condensed water generated exceeds the allowable limit. There is a risk of being squeezed by a valve.

  Then, an object of this invention is to provide the exhaust gas recirculation apparatus of the internal combustion engine which can suppress that the condensed water produced | generated with the exhaust gas recirculation apparatus leaks outside.

Exhaust reflux device of the present invention, the exhaust gas recirculation passage for introducing the intake system part of exhaust gas of an internal combustion engine as EGR gas, a cooling means provided in the exhaust gas recirculation passage, the downstream side of the cooling means An exhaust gas recirculation control valve provided in the exhaust gas recirculation passage, the opening degree of which can be adjusted from a fully closed position that fully closes the exhaust gas recirculation passage to a fully open position that fully opens the exhaust gas recirculation passage; and operation of the internal combustion engine Exhaust recirculation control means for controlling the opening degree of the exhaust gas recirculation control valve according to the state, and the exhaust recirculation control means is provided when an introduction blocking condition for interrupting introduction of the exhaust recirculation gas is satisfied. While the exhaust gas recirculation control valve is controlled to the fully closed position, and the amount of condensed water generated in the exhaust gas recirculation passage exceeds an allowable limit, the introduction blocking condition is satisfied. The exhaust return to the intake system By the control of the opening degree of the exhaust gas recirculation control valve wherein a predetermined opening side of the opening than the fully closed position, as the introduction of the gas is allowed to solve the problems mentioned above (claim 1).

According to exhaust recirculation system this, when the generation amount of condensed water generated in the exhaust passage exceeds the allowable limit, the predetermined opening-side of the opening than the opening degree of the exhaust gas recirculation control valve is fully closed position Controlled. Therefore, when the amount of condensed water generated in the exhaust gas recirculation passage exceeds the allowable limit, the exhaust gas recirculation passage is throttled by the exhaust gas recirculation control valve, so that the pressure in the exhaust gas recirculation passage rises and the pressure is increased. Therefore, it is possible to suppress the condensed water from leaking outside the exhaust gas recirculation passage. Various places where condensed water may leak out are assumed depending on the configuration of the exhaust gas recirculation device. For example, the exhaust gas recirculation device is configured such that a bypass passage that bypasses the cooling means provided in the exhaust gas recirculation passage, a valve body that opens and closes the bypass passage, and the valve body is provided so as to be integrally rotatable and penetrate the bypass passage. When the valve shaft that is exposed to the outside is provided, the condensed water may leak to the outside through the valve shaft at a location where the valve shaft is exposed to the outside. According to exhaust recirculation system of the present invention, the condensed water so the amount of condensed water is avoided that the exhaust gas recirculation passage is throttled by the exhaust gas recirculation control valve in situations exceeds a predetermined limit even in this structure Leakage to the outside can be suppressed. The introduction of the exhaust gas recirculation gas into the intake system is performed in order to lower the combustion temperature and reduce the nitrogen oxide in the exhaust gas. However, there is an operation region where smoke is generated by introducing the exhaust gas recirculation gas. Exhaust recirculation system This exhaust gas recirculation control as the introduction of exhaust gas recirculation gas to suppress the generation of smoke is interrupted when when the internal combustion engine is in such operating region, i.e. the introduction cutoff condition is satisfied While the valve is controlled to the fully closed position, the exhaust gas recirculation control valve is opened when the amount of condensed water generated exceeds a predetermined limit. Therefore, even if the introduction shut-off condition is satisfied when the amount of condensed water generated exceeds the allowable limit, the condensed water is blocked by closing the exhaust gas recirculation passage with the exhaust gas recirculation control valve. Can be prevented.

The amount of condensed water produced can be obtained by various methods. For example, a level sensor capable of detecting the level of condensed water in the exhaust gas recirculation passage may be provided, and the amount of condensed water generated may be obtained directly from the sensor, or based on a physical quantity correlated with the amount of condensed water generated. May be estimated. For example, the exhaust gas recirculation control means estimates the amount of condensed water generation based on a duration during which the gas temperature of the exhaust gas recirculation gas downstream of the cooling means is below a predetermined temperature. An estimation unit and a limit water amount determination unit that determines whether the amount of condensed water generated exceeds the allowable limit based on whether or not the duration time exceeds a threshold value ( claim 2). ). When the gas temperature of the exhaust gas recirculation gas on the downstream side of the cooling means is below a predetermined temperature, the generated condensed water does not evaporate due to the heat of the exhaust gas recirculation gas, and the generated condensed water tends to increase. . Therefore, it is possible to estimate the amount of condensed water generated based on the duration for which the state of the predetermined temperature or lower continues. Since the amount of condensed water generated increases as the duration increases, it is possible to determine whether or not an allowable limit has been exceeded by setting a threshold value for the duration.

  As described above, according to the exhaust gas recirculation apparatus of the present invention, when the amount of condensed water generated in the exhaust passage exceeds the allowable limit, the opening degree of the exhaust gas recirculation control valve is set to be greater than the fully closed position. Since the amount of condensed water generated exceeds the allowable limit, the pressure in the exhaust gas recirculation passage rises when the exhaust gas recirculation passage is throttled by the exhaust gas recirculation control valve. This makes it possible to prevent the condensed water from leaking outside the exhaust gas recirculation passage.

  FIG. 1 is a schematic cross-sectional view showing the main part of the internal configuration of an exhaust gas recirculation apparatus according to an embodiment of the present invention. The exhaust gas recirculation device 1 has an exhaust gas recirculation passage 2 for extracting a part of exhaust gas (exhaust gas recirculation gas) of the internal combustion engine, and the exhaust gas recirculation passage 2 includes a cooling unit 3 for cooling the exhaust gas recirculation gas, and An exhaust gas recirculation control valve 4 is provided on the downstream side of the cooling unit 3 to adjust the flow rate of the exhaust gas recirculation gas. The exhaust gas recirculation passage 2 has one upstream end connected to an exhaust system 100 of an internal combustion engine such as an exhaust manifold and the other downstream end connected to an intake system 101 of an internal combustion engine such as an intake manifold.

The cooling unit 3 includes a cylindrical main body portion 31 provided with a partition wall 33 extending so as to divide the exhaust gas recirculation passage 2 into two passages, and a passage switching portion 32 connected to the downstream side of the main body portion 31. ing. A heat exchanger 36 serving as a cooling means is disposed in one passage 34 divided by the partition wall 33. The other passage 35 divided by the partition wall 33 functions as a bypass passage that bypasses the heat exchanger 36. The partition wall 33 extends to the boundary between the main body portion 31 and the passage switching portion 32. The heat exchanger 36 included in the main body 31 discharges the refrigerant such as cooling water introduced from the introduction port 36a from the discharge port 36b and circulates the refrigerant, whereby the exhaust gas recirculation gas and the refrigerant introduced into the heat exchanger 36 are circulated. It is configured so that can heat exchange between. The exhaust gas recirculation passage 2 (passage 34) on the downstream side of the heat exchanger 36 is provided with a temperature sensor 5 that outputs a signal corresponding to the gas temperature of the exhaust gas recirculation gas.

  The passage switching unit 32 is connected to the passage 34 of the main body 31 to constitute a part of the exhaust gas recirculation passage 2 and is connected to the passage 35 of the main body 31 to constitute a part of the bypass passage. A housing 37 having a second passage 37b is provided. Each of the passages 37a and 37b is provided with a plate-like valve body 38 configured to correspond to the shape of the passage. Each valve body 38 is attached to the valve shaft 39 by fastening means such as a bolt, and the valve shaft 39 extends across the first passage 37a and the second passage 37b, and has one end on the second passage 37b side. Is exposed to the outside of the housing 37. The housing 37 rotatably supports the valve shaft 39, and the passage switching unit 32 is configured such that each valve body 38 can rotate integrally with the valve shaft 39 around the rotation axis CL of the valve shaft 39.

  Each valve body 38 is attached to the valve shaft 39 such that the attachment position of the valve body 38 of the first passage 37a and the valve body 38 of the second passage 37b is shifted from each other by approximately 90 ° with respect to the valve shaft 39. . Therefore, when the first passage 37a is opened by the valve body 38, the second passage 37b is closed by the valve body 38, and conversely, when the first passage 37a is closed by the valve body 38, the second passage 37b is closed. The two passages 37b are opened by the valve body 38. That is, the passage switching unit 32 changes the rotational position of the valve shaft 39 to open the exhaust gas recirculation passage (first passage 37a) while closing the bypass passage (second passage 37b), and the exhaust gas recirculation. It functions as a path switching means that can switch between a bypass position that closes the path and opens the bypass path. FIG. 1 shows the state of the passing position. The valve shaft 39 is rotationally driven by an actuator 40 linked to one end thereof. The operation of the actuator 40 is controlled by an engine control unit 10 which will be described later, but since the control may be the same as a known one, a detailed description thereof will be omitted.

  The exhaust gas recirculation control valve 4 is disposed in the exhaust gas recirculation passage 2 on the downstream side of the cooling unit 3 so that the opening degree can be adjusted from the fully closed position P1 where the exhaust gas recirculation passage 2 is fully closed to the fully open position P2 where the exhaust recirculation passage 2 is fully opened. It is configured. FIG. 1 shows the state of the fully closed position P1. The exhaust gas recirculation control valve 4 is seated on a valve seat 2a formed in the exhaust gas recirculation passage 2 and can close the exhaust gas recirculation passage 2, an actuator 42 for driving the valve body 41, a valve body 41, A valve shaft 43 that connects the actuator 42 is provided. The actuator 42 is connected to an engine control unit (ECU) 10 for appropriately controlling the operating state of the internal combustion engine, and the operation of the actuator 42 is controlled by the ECU 10. The ECU 10 includes a temperature sensor 5 described above, a rotational speed sensor 6 that outputs a signal corresponding to the engine rotational speed (rotational speed) of the internal combustion engine, and an accelerator opening sensor 7 that outputs a signal corresponding to the accelerator opening of the internal combustion engine. Are connected to each other. In addition to these sensors, various sensors are connected to the ECU 10, but illustration thereof is omitted.

  Next, control of the exhaust gas recirculation device 1 will be described with reference to FIGS. FIG. 2 is a flowchart showing an example of an exhaust gas recirculation control routine that the ECU 10 repeatedly executes at predetermined intervals. The program of this routine is stored in storage means such as a ROM built in the ECU 10, and the ECU 10 reads the program from the storage means as appropriate and executes it. First, in step S1, the ECU 10 acquires the operating state of the internal combustion engine, for example, the engine speed Ne and the fuel injection amount (load) Q. The engine speed Ne can be acquired based on a signal from the speed sensor 6. The fuel injection amount Q is stored in advance in a storage means, for example, with the accelerator opening and the engine speed Ne as variables, and the map is referred to the signals from the rotation speed sensor 6 and the accelerator opening sensor 7. It can be acquired by referring.

  In step S2, in order to control the exhaust gas recirculation control valve 4 so that the opening degree of the exhaust gas recirculation control valve 4 corresponds to the operating state of the internal combustion engine, the EGR execution region AR1 or the exhaust gas recirculation gas for introducing the exhaust gas recirculation gas is controlled. It is determined which one of the EGR cut areas AR2 to block the introduction of. For this determination, for example, as shown in FIG. 3, a map defining the areas AR1 and AR2 with the fuel injection amount Q and the engine speed Ne as variables is stored in the storage means, and this map is referred to. realizable.

Next, the ECU 10 proceeds to step S4 if the region determined in step S2 is the EGR execution region AR1, and proceeds to step S5 if the region is the EGR cut region (step S3). In step S4, the exhaust gas recirculation control valve 4 is controlled (normal control) so that the opening degree x corresponds to the operating state of the internal combustion engine, and then the current routine is terminated.

  In step S5, the amount of condensed water qw generated in the exhaust gas recirculation passage 2 is estimated. In this embodiment, the amount of condensed water generated qw is estimated based on the gas temperature of the exhaust gas recirculation gas on the downstream side of the heat exchanger 36 and the duration α during which the gas temperature remains below a predetermined temperature. The ECU 10 has a function of detecting the gas temperature of the exhaust gas recirculation gas on the downstream side of the heat exchanger 36 based on a signal from the temperature sensor 5 and measuring a duration time during which the temperature is equal to or lower than a predetermined temperature. When the temperature exceeds the predetermined temperature, the counter for measuring the duration time is reset, and thereafter, the measurement of the duration time is started when the temperature falls below the predetermined temperature.

  In a succeeding step S6, it is determined whether or not the amount of condensed water generated qw is within an allowable limit. In this embodiment, a threshold value β for the duration corresponding to the allowable limit is set in advance. Therefore, if the duration α measured in step S5 is less than the threshold β (α <β), there is no inconvenience even if the exhaust gas recirculation control valve 4 is in the fully closed position (opening = 0) in that state. It is determined that the value is within the limit, the process proceeds to step S7, the exhaust gas recirculation control valve 4 is controlled so that the opening degree of the exhaust gas recirculation control valve 4 becomes 0, and the current routine is ended. The threshold value β is appropriately set according to the configuration of the exhaust gas recirculation device 1, and this threshold value β may be changed according to the operating state of the internal combustion engine, or may be fixed regardless of the operating state. . The threshold value β has a significance as a value with which it can be determined whether or not condensed water that leaks to the outside is generated.

  On the other hand, when the duration time α measured in step S5 is equal to or greater than the threshold value β (α ≧ β), the process proceeds to step S8, and exhaust is performed so that a predetermined opening side opening degree = a (a ≠ 0). The reflux control valve 4 is controlled. This control is maintained until A second elapses (step S9). As a result, the condensed water generated in the exhaust gas recirculation passage 2 can be reduced by being evaporated by the flow of the exhaust gas recirculation gas. The opening degree a and the time A seconds are set as long as the amount of smoke generated due to the introduction of the exhaust gas recirculation gas does not exceed the allowable value. Preferably, the opening degree a and the time A seconds are set to be as large as possible within the limit. If it is determined in step S9 that A seconds have elapsed, the current routine is terminated.

  According to the above embodiment, when the internal combustion engine belongs to the EGR cut area AR2, that is, when the introduction cutoff condition is satisfied, the exhaust gas recirculation control valve 4 is shut off so that the introduction of the exhaust gas recirculation gas is blocked to suppress the generation of smoke. The exhaust recirculation control valve 4 is opened when the amount of condensed water generated exceeds a predetermined limit, and the introduction is shut off when the amount of condensed water exceeds the allowable limit. Even if the condition is satisfied, it is possible to prevent the condensed water from being blocked by closing the exhaust gas recirculation passage 2 with the exhaust gas recirculation control valve 4. Thereby, the pressure in the exhaust gas recirculation passage 2 rises, and it is possible to suppress the condensed water from leaking outside the exhaust gas recirculation passage 2 due to the pressure.

In the above embodiment, by executing the control routine of FIG. 2, the ECU 10 executes exhaust gas recirculation control means, and by executing step S5 of FIG. 2, ECU 10 executes step S6 of FIG. 2 as condensed water generation amount estimation means. Thus, the ECU 10 functions as a limit water amount determination unit. However, this invention is not limited to the above form, You may implement with a various form. In the illustrated form, the cooling means and the bypass passage are integrated, but the present invention may be implemented as a form in which these are separated. Moreover, although the passage switching unit of the cooling unit is connected to the outlet side, the present invention may be implemented in a form connected to the inlet side.

In the above embodiment, the exhaust gas recirculation control valve 4 is controlled so that the opening degree of the exhaust gas recirculation control valve 4 becomes a (a ≠ 0) without blocking the introduction of the exhaust gas recirculation gas when belonging to the EGR cut region AR2. (Steps S3, S6, S8, and S9 in FIG. 2), even in the EGR execution area AR1, the operation of the internal combustion engine is performed when the amount of condensed water generated exceeds the allowable limit. without controlling the opening degree x that is set in accordance with the state, the opening degree of the exhaust gas recirculation control valve 4 may be controlled exhaust gas recirculation control valve 4 such that a (a ≠ 0 and a ≧ x) . By doing so, it is possible to avoid the exhaust gas recirculation passage 2 being throttled by the exhaust gas recirculation control valve 4 when the amount of condensed water generated exceeds the allowable limit.

  The gas temperature downstream of the heat exchanger 36 may not be detected directly from the temperature sensor 5 but may be estimated from a physical quantity correlated with the exhaust gas recirculation gas temperature. For example, a map that gives the exhaust gas recirculation gas temperature with the cooling water temperature of the internal combustion engine (refrigerant temperature of the heat exchanger 36) and the fuel injection amount of the internal combustion engine as variables is stored in advance in the storage means, and this is referred to by referring to this map. The gas temperature may be estimated.

  As shown in FIG. 4, the amount of condensed water generated is determined by providing the condensed water holding unit 50 that can store condensed water in the exhaust gas recirculation passage 2 and the level X of the condensed water accumulated in the holding unit 50. The level sensor 51 to detect may be provided, and it may acquire directly from the output of the level sensor 51. In addition, the generation amount may be estimated from a physical quantity that correlates with the generation amount of condensed water different from the gas temperature and duration described above, or a means for detecting the generation amount itself is provided, and the generation amount is determined from the means. You may obtain it directly.

The cross-sectional schematic diagram which showed the principal part of the internal structure of the exhaust gas recirculation apparatus which concerns on embodiment of this invention. 6 is a flowchart showing an example of an exhaust gas recirculation control routine according to the embodiment. The schematic diagram which showed an example of the map which defined area | region AR1, AR2 by making fuel injection quantity Q and engine speed Ne into a variable. Explanatory drawing explaining the other form of this invention.

Explanation of symbols

1 Exhaust gas recirculation device 2 Exhaust gas recirculation passage 4 Exhaust gas recirculation control valve 10 ECU (Exhaust gas recirculation control means, condensate water generation amount estimation means, limit water amount determination means)
32 passage switching part (passage switching means)
33 Bulkhead 36 Heat exchanger (cooling means)
101 Intake system P1 Fully closed position P2 Fully open position

Claims (2)

An exhaust gas recirculation passage for introducing a part of the exhaust gas of the internal combustion engine into the intake system as exhaust gas recirculation gas, cooling means provided in the exhaust gas recirculation passage, provided in the exhaust gas recirculation passage on the downstream side of the cooling means, An exhaust gas recirculation control valve whose opening degree can be adjusted from a fully closed position where the exhaust gas recirculation passage is fully closed to a fully open position where the exhaust gas recirculation passage is fully opened, and the exhaust gas recirculation control valve according to the operating state of the internal combustion engine An exhaust gas recirculation control means for controlling the opening degree of
The exhaust gas recirculation control means controls the exhaust gas recirculation control valve to the fully closed position when an introduction cutoff condition for interrupting the introduction of the exhaust gas recirculation gas is satisfied, while condensing generated in the exhaust gas recirculation passage. When the amount of water generated exceeds an allowable limit, the exhaust gas recirculation control valve of the exhaust gas recirculation control valve is allowed to allow introduction of the exhaust gas recirculation gas into the intake system even when the introduction cutoff condition is satisfied. An exhaust gas recirculation device for an internal combustion engine, wherein an opening degree is controlled to a predetermined opening degree that is on an opening side of the fully closed position.   The exhaust gas recirculation control means estimates the amount of condensed water generation based on a duration during which the gas temperature of the exhaust gas recirculation gas on the downstream side of the cooling means continues below a predetermined temperature. And limiting water amount determination means for determining whether or not the amount of condensed water produced exceeds the allowable limit based on whether or not the duration time exceeds a threshold value. An exhaust gas recirculation device for an internal combustion engine as described.

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