JP4924531B2 - Internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine including an EGR device capable of guiding a part of exhaust gas from an exhaust passage to an intake passage.

  2. Description of the Related Art An EGR (exhaust gas recirculation) device that guides a part of exhaust gas discharged from a cylinder to an intake passage and flows again into the cylinder is known for the purpose of reducing pump loss in an internal combustion engine. An EGR device generally includes an EGR passage that connects an exhaust passage and an intake passage, an EGR valve that adjusts the flow rate of exhaust gas that flows toward the intake passage through the EGR passage (hereinafter referred to as EGR gas), and the like. (For example, see Patent Documents 1 and 2). Patent Document 1 below discloses a control technique for controlling the opening degree of the EGR valve in accordance with the operating state of the internal combustion engine such as the intake air amount and the pressure of the EGR gas flowing through the EGR passage.

JP-A-7-174048 JP 2004-100508 A

  By the way, depending on the operating state of the internal combustion engine, such as when the engine load is high, the negative pressure of the intake passage through which the EGR gas flows may be reduced, that is, the pressure in the intake passage may be increased. In some cases, the pressure difference between the intake pressure and the pressure in the exhaust passage into which the EGR gas is taken (hereinafter referred to as exhaust pressure) becomes small. When the pressure difference is small as described above, it may be difficult to guide the EGR gas having a desired flow rate to the intake passage even if the EGR device is operated by opening the EGR valve or the like.

  In the above-mentioned Patent Document 2, a supercharger that supercharges EGR gas is provided in the middle of the EGR passage (EGR pipe), and supercharged EGR gas is guided to the intake passage so that the intake pressure (supply pressure) is increased. It has been proposed that the flow rate of EGR gas flowing into the intake passage is ensured even in an operation state in which the pressure between the air pressure and the exhaust pressure is small. However, providing a supercharger for an EGR device in the internal combustion engine has problems such as a complicated structure of the internal combustion engine.

  Therefore, in an internal combustion engine equipped with an EGR device, when the EGR device is operated to take in EGR gas from the exhaust passage and guide it to the intake passage, the pressure difference between the intake pressure and the exhaust pressure is increased. It is desired to realize a technique capable of increasing the flow rate of the EGR gas led to the above with a simple configuration.

  The present invention has been made in view of the above, and an internal combustion engine capable of increasing the flow rate of EGR gas by increasing the pressure difference between the intake pressure and the exhaust pressure when guiding EGR gas to the intake passage. The purpose is to provide an institution.

  In order to achieve the above object, an internal combustion engine according to the present invention includes an EGR device capable of guiding a part of exhaust gas from an exhaust passage as EGR gas to an intake passage, and a plurality of cooling water passages are provided in the engine. An internal combustion engine provided in the main body, the flow rate adjusting means capable of adjusting an exhaust side cooling water flow rate which is a flow rate of cooling water flowing through a cooling water passage closest to an exhaust passage among a plurality of cooling water passages; Control means capable of controlling the apparatus and the flow rate adjusting means, wherein the control means reduces the exhaust-side cooling water flow rate by the flow rate adjusting means when the EGR gas is guided to the intake passage by the EGR device. To do.

  In the internal combustion engine, the EGR device includes an EGR cooler that cools EGR gas, and the EGR cooler is configured such that an EGR-side cooling water flow rate that is a flow rate of the coolant flowing through is adjusted by a flow rate adjusting unit. The control means may reduce the exhaust-side cooling water flow rate and increase the EGR-side cooling water flow rate by the flow rate adjusting means.

  In the internal combustion engine, the flow rate adjusting means diverts the cooling water from the cooling water pump into an EGR side cooling water passage that passes through the EGR cooler and an exhaust side cooling water passage that is the cooling water passage closest to the exhaust passage. It is a diversion valve, and the control means can control the flow rate distribution ratio of the diversion valve to increase the EGR side cooling water flow rate by the amount of reducing the exhaust side cooling water flow rate.

  In the internal combustion engine, the control means determines whether or not the pumping flow rate control means that controls the pumping flow rate that is the cooling water flow rate that the cooling water pump pumps at least toward the flow rate adjusting means, and whether the flow rate adjusting means is out of order. An exhaust temperature determining means for determining whether the exhaust temperature of the exhaust gas flowing through the exhaust passage exceeds a preset upper limit value when it is determined that the failure determining means and the flow rate adjusting means are malfunctioning If the exhaust gas temperature is determined to exceed the upper limit, the pumping flow rate of the cooling water pump can be increased.

  According to the present invention, the control means reduces the flow rate of the exhaust-side cooling water flowing through the cooling water passage closest to the exhaust passage and raises the exhaust gas temperature, which is the temperature of the exhaust gas flowing through the exhaust passage. The exhaust pressure, which is the internal pressure, can be increased, and the flow rate of EGR gas can be increased by increasing the pressure difference between the exhaust pressure and the intake pressure.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment (hereinafter referred to as an embodiment). In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

Embodiment 1
First, the configuration of the internal combustion engine according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram showing a schematic configuration of an internal combustion engine. In FIG. 1, only the main part related to the present invention is schematically shown.

  The internal combustion engine 10 is a piston reciprocating engine and is mounted on an automobile as a prime mover. The internal combustion engine 10 is provided with an electronic control unit 100 (hereinafter referred to as ECU) as a control means for controlling this, that is, a control device for the internal combustion engine. The ECU 100 has a ROM as storage means for storing various control constants. In the present embodiment, the ECU 100 as the control means is included in the internal combustion engine 10.

  The internal combustion engine 10 is provided with a cylinder block, a cylinder head, an engine output shaft (crankshaft), etc., not shown, as components constituting the engine body 20. The cylinder block is formed with a cylinder bore in which a piston reciprocates. The cylinder head is coupled to the cylinder block so as to surround the cylinder bore so as to face the piston. In this way, a “cylinder” is formed in the engine body 20 by being surrounded by the cylinder bore, the cylinder head, and the piston. In the present embodiment, the engine body 20 is formed with a plurality of cylinders.

  The mechanical power generated by the internal combustion engine 10 is output from a crankshaft as the engine output shaft. The internal combustion engine 10 is provided with a crank angle sensor (not shown) that detects a rotation angle position of the crankshaft (hereinafter referred to as a crank angle), and sends a signal related to the detected crank angle to the ECU 100. Yes.

  The cylinder head of the engine body 20 of the internal combustion engine 10 is provided with an intake port (not shown) for guiding intake air into the cylinder corresponding to the cylinder. An intake manifold (a surge chamber is indicated by reference numeral 26 in the figure), which is a distribution pipe that distributes intake air to each cylinder, is connected to the intake port. A throttle valve 24 for adjusting the flow rate of the intake air flowing into the intake manifold is provided on the upstream side of the intake manifold in the flow direction of the intake air. The opening degree of the throttle valve 24, that is, the flow rate of the intake air flowing into the intake manifold is controlled by the ECU 100.

  The “intake passage” is a passage through which intake air flows, and means a passage downstream of the throttle valve 24 in the flow direction of intake air. In the present embodiment, the intake passage includes an intake port of the cylinder head in addition to the intake air passage formed in the intake manifold.

  The internal combustion engine 10 is provided with an air flow meter (not shown) as means for measuring the intake air amount upstream of the throttle valve 24 in order to guide the intake air from the outside air into the cylinder. . The air flow meter measures the flow rate of intake air flowing into the cylinder through the throttle valve 24 (hereinafter referred to as “intake air amount”), and sends a signal related to the measured intake air amount to the ECU 100. Sending out.

  Further, an exhaust port (not shown) for exhausting exhaust gas from the cylinder is formed in the cylinder head of the engine body 20 of the internal combustion engine 10 corresponding to the cylinder. Connected to the exhaust port is an exhaust manifold (not shown) that is a merging pipe for merging exhaust gases from the cylinders. In the present embodiment, the exhaust manifold is formed integrally with the cylinder head and is included in the engine body 20. The joining portion of the exhaust manifold is indicated by reference numeral 60 in the figure. The exhaust manifold may be configured separately from the cylinder head.

  An exhaust purification catalytic converter (hereinafter simply referred to as “exhaust purification catalyst”) 66 for purifying and reducing harmful components in the exhaust gas is provided on the downstream side of the exhaust manifold in the flow direction of the exhaust manifold. Examples of the exhaust purification catalyst 66 include a three-way catalyst and a NOx occlusion reduction type catalyst, and a noble metal having a catalytic action is used.

  The “exhaust passage” is a passage through which the exhaust gas flows, and means a passage on the upstream side of the exhaust purification catalyst 66 in the flow direction of the exhaust gas. In the present embodiment, the exhaust passage includes an exhaust gas passage formed in the exhaust manifold and an exhaust port of the cylinder head.

  Further, the internal combustion engine 10 is provided with an EGR (exhaust gas recirculation) device 70 that guides a part of the exhaust gas flowing through the exhaust passage to the intake passage as EGR gas and again flows into the cylinder. The EGR device 70 includes an EGR passage 72 that connects the exhaust passage and the intake passage, an EGR valve 74 that adjusts the flow rate of exhaust gas flowing through the EGR passage 72 (hereinafter referred to as EGR gas), and an EGR that cools the EGR gas. And a cooler 77.

  In the EGR passage 72, an intake port for taking in exhaust gas from the exhaust passage is provided in the merging portion 60 of the exhaust manifold, while an outlet port for flowing EGR gas, which is exhaust gas taken in from the intake port, into the intake passage. Provided on the manifold. The EGR passage 72 can take a part of the exhaust gas flowing through the exhaust passage from the intake port and guide it from the outlet port to the intake passage as EGR gas. An EGR valve 74 is provided in the middle of the EGR passage 72.

  The EGR valve 74 is composed of a flow control valve such as a throttle valve, and the flow rate of EGR gas guided from the EGR passage 72 to the intake passage can be adjusted by adjusting the valve opening degree. . The valve opening degree of the EGR valve 74 is configured to be controllable by the ECU 100.

  The EGR cooler 77 is composed of a heat exchanger, and is provided in the EGR passage 72, specifically, on the upstream side in the EGR gas flow direction from the EGR valve 74. The EGR cooler 77 has a cooling water passage 35 provided therein, and the EGR gas passing therethrough can be cooled by exchanging heat between the cooling water flowing through the cooling water passage 35 and the EGR gas. It is configured.

  The EGR device 70 configured as described above opens the EGR valve 74 so that the pressure difference between the pressure in the exhaust passage (hereinafter referred to as exhaust pressure) and the pressure in the intake passage (hereinafter referred to as intake pressure). , A part of the exhaust gas flowing through the exhaust passage is taken into the EGR passage 72. After the EGR gas taken into the EGR passage 72 is cooled by the EGR cooler 77, the flow rate is adjusted by the EGR valve 74 and guided to the intake passage so that it can flow into the cylinder again. In this way, the flow rate of the EGR gas that the EGR device 70 leads from the exhaust passage to the intake passage is controlled by the ECU 100 via the EGR valve 74. That is, the EGR device 70 is configured to be controllable by the ECU 100.

  Further, the engine body 20 of the internal combustion engine 10 is provided with a plurality of cooling water passages 33, 34. Of these cooling water passages 33, 34, the most exhaust passage side, more specifically, the most exhaust port side. The cooling water passage 34 that is set to pass therethrough will be referred to as an “exhaust-side cooling water passage” hereinafter. On the other hand, the cooling water passage 33 other than the exhaust side cooling water passage 34 among the cooling water passages passing through the engine main body 20 is hereinafter referred to as “another cooling water passage”. The exhaust side cooling water passage 34 and the other cooling water passage 33 are extended from the engine body 20 in addition to the passages formed in the parts constituting the engine body 20 such as the cylinder block, the cylinder head, and the exhaust manifold. It includes a passage (pipe) formed inside a cooling pipe or the like.

  In the internal combustion engine 10, heat exchange can be performed between the cooling water flowing through the exhaust-side cooling water passage 34 and the exhaust gas discharged from the cylinder and flowing through the exhaust passage. By reducing the flow rate of the cooling water flowing through the exhaust side cooling water passage 34 (hereinafter referred to as the exhaust side cooling water flow rate), the temperature of the exhaust gas discharged from the cylinder and directed to the exhaust purification catalyst 66 (hereinafter referred to as the exhaust side cooling water flow rate). It is possible to raise the exhaust temperature).

  In the present embodiment, the exhaust-side cooling water passage 34 is set so as to pass through the exhaust passage side of the cylinder head constituting the engine body 20 and the exhaust manifold formed integrally with the cylinder head. . The exhaust-side cooling water passage 34 may be set to pass through the cylinder head, and the other cooling water passages 33 may be set to pass through the cylinder block.

  On the other hand, the other cooling water passage 33 is a cooling water passage that is set so as not to pass through the vicinity of the exhaust port, and a change in the flow rate of the cooling water flowing through the passage is transferred to the exhaust-side cooling water passage 34 described above. Compared to the cooling water passage, the cooling water passage has less influence on the exhaust temperature. By adjusting the flow rate of the cooling water flowing through the other cooling water passages 33, it is possible to adjust the temperature of a portion of the engine body 20 that does not significantly affect the exhaust temperature, such as a cylinder block.

  Further, the internal combustion engine 10 is provided with a cooling water passage (hereinafter referred to as an EGR side cooling water passage) 35 having a route set to flow through the EGR cooler 77 of the EGR device 70. The EGR side cooling water passage 35 includes a passage (pipe) formed inside a cooling pipe or the like extending from the EGR cooler 77 in addition to a passage formed in the EGR cooler 77. The cooling water flowing through the EGR side cooling water passage 35 is used for cooling the EGR gas flowing through the EGR passage 72. By increasing the flow rate of the cooling water flowing through the EGR side cooling water passage 35 (hereinafter referred to as the EGR side cooling water flow rate), it is possible to increase the density of the EGR gas toward the intake passage.

  Further, the cooling water is pumped to the internal combustion engine 10 toward the EGR side cooling water passage 35, the exhaust side cooling water passage 34, and the other cooling water passages 33 as cooling system parts for cooling the engine body 20 and the EGR cooler. The cooling water pump 30, the cooling water from the cooling water pump 30 to the EGR side cooling water passage 35, the diversion valve 44 for diverting the cooling water to the exhaust side cooling water passage 34, and these cooling water passages A radiator 80 that dissipates and cools the heat of the cooling water that has flowed through 33, 34, and 35 to the outside air, and a thermostat valve 40 that switches whether or not the cooling water is allowed to flow through the radiator 80 are provided.

  The cooling water pump 30 is driven by mechanical power generated by the internal combustion engine 10. The cooling water pump 30 is a mechanical pump that is driven by transmitting mechanical power output from a crankshaft via a pulley, a belt, or the like (not shown). The cooling water pump 30 is driven by mechanical power from the internal combustion engine 10 and pumps it to the feed cooling water passage 31. This feed cooling water passage 31 is branched into another cooling water passage 33 and a cooling water passage 32 directed to the diversion valve 44, and the cooling water pumped by the cooling water pump 30 is transferred to the other cooling water passage 33. The cooling water is diverted to the cooling water going to and the cooling water going to the diversion valve 44.

  During operation of the internal combustion engine 10, the cooling water pump 30 is always driven, and the cooling water from the thermostat valve 40 is pumped toward the other cooling water passage 33 and the diversion valve 44. The flow rate of the cooling water pumped by the pump 30 is substantially proportional to the rotational speed of the crankshaft of the internal combustion engine 10 (hereinafter referred to as engine rotational speed).

  The thermostat valve 40 flows through the other cooling water passage 33, the exhaust side cooling water passage 34, and the EGR side cooling water passage 35, and combines the cooling water merged in the return cooling water passage 36 according to the temperature of the cooling water. In addition, it is possible to switch between flowing on the radiator side cooling water passage 38 that flows through the radiator 80 or flowing to the bypass cooling water passage 37 provided so as to bypass the radiator 80. Before the warm-up of the internal combustion engine 10 is completed, the opening / closing valve of the thermostat valve 40 is set in advance so that the coolant flows around the radiator 80. The thermostat valve 40 flows the cooling water that has flowed through the radiator side cooling water passage 38 and the bypass cooling water passage 37 toward the cooling water pump 30 via the cooling water passage 42.

  The diversion valve 44 is configured by a so-called three-way valve, and cooling toward the other cooling water passage 33 among the cooling water from the cooling water passage 32, that is, the cooling water pumped by the cooling water pump 30 to the feed cooling water passage 31. Receiving the cooling water other than water, it is divided into the cooling water toward the exhaust side cooling water passage 34 and the cooling water toward the EGR side cooling water passage 35. That is, the diversion valve 44 reduces the opening degree on the exhaust side cooling water passage 34 side, so that the flow rate of the cooling water flowing through the exhaust side cooling water passage 34 regardless of the operating state (engine speed) of the internal combustion engine 10. It functions as a flow rate adjusting means for adjusting the exhaust-side cooling water flow rate. In addition, the diversion valve 44 can increase the flow rate of the EGR side cooling water flowing through the EGR side cooling water passage 35 by the amount by which the flow rate of the exhaust side cooling water flowing through the exhaust side cooling water passage 34 is reduced. Yes. The valve opening degree of the diversion valve 44, that is, the ratio (hereinafter referred to as the flow distribution ratio) of distributing the cooling water flow rate to the exhaust side cooling water passage 34 in the supplied cooling water flow rate can be controlled by the ECU 100. It is configured.

  The cooling water pumped by the cooling water pump 30 is diverted from the feed cooling water passage 31 to the cooling water passage 32 directed to the diversion valve 44 and the other cooling water passage 33 directed to the engine main body 20. The main body 20 is divided (distributed) into an exhaust side cooling water passage 34 passing through the exhaust passage side most and an EGR side cooling water passage 35. Cooling water that has flowed through the exhaust side cooling water passage 34, the other cooling water passage 33, and the EGR side cooling water passage 35 and has reached a high temperature joins in the return cooling water passage 36. The cooling water flowing through the return cooling water passage 36 toward the thermostat valve 40 passes through one of the radiator side cooling water passage 38 passing through the radiator 80 and the bypass cooling water passage 39 bypassing the radiator 80. 40. The relatively low temperature cooling water that has flowed into the thermostat valve 40 is drawn into the cooling water pump 30 from the cooling water passage 42.

  In the internal combustion engine 10 configured as described above, the ECU 100 detects a signal related to the crank angle from the crank angle sensor, and the rotational speed of the crank shaft (engine output shaft) of the internal combustion engine 10 (hereinafter referred to as engine rotation). The speed is estimated as a control variable. Further, the ECU 100 detects a signal related to the intake air amount from the air flow meter, and estimates the torque (hereinafter referred to as engine load) output from the crankshaft by the internal combustion engine 10 as a control variable. As described above, the ECU 100 has a function of estimating the engine speed and the engine load indicating the operation state of the internal combustion engine 10 as control variables.

  Further, the ECU 100 has a function of estimating a coolant flow rate (hereinafter, referred to as a pumped flow rate) that the coolant pump 30 pumps based on the engine speed of the internal combustion engine 10. Further, the ECU 100 determines an opening degree of the diversion valve 44, that is, a flow rate distribution ratio that is a ratio of the exhaust side cooling water flow rate and the EGR side cooling water flow rate, based on the operating state of the internal combustion engine 10, that is, the engine speed and the engine load. I have control. The ECU 100 calculates the exhaust-side cooling water flow rate flowing through the exhaust-side cooling water passage 34 and the EGR-side cooling water flow rate flowing through the EGR-side cooling water passage 35 from the pumping flow rate of the cooling water pump 30 and the flow rate distribution ratio of the diversion valve 44. Each has a function of estimating as a control variable.

  Further, the ECU 100 has a function of estimating the temperature of exhaust gas flowing in the exhaust passage toward the exhaust purification catalyst 66 (hereinafter referred to as exhaust temperature) based on the engine rotation speed and the engine load. A map indicating the engine rotation speed of the internal combustion engine 10 and the exhaust temperature with respect to the engine load is obtained in advance by a matching experiment or the like, and is stored in the ROM of the ECU 100 as a control constant.

  The ECU 100 is configured to be able to estimate the exhaust temperature in the exhaust purification catalyst 66 based on the operating state of the internal combustion engine 10, that is, the engine speed and the engine load. A map showing the relationship between the engine speed and the engine load and the exhaust temperature is obtained in advance by a matching experiment or the like, and is stored in a ROM (not shown) of the ECU 100 as a control constant. Thus, the ECU 100 has a function of estimating the exhaust temperature as a control variable.

  As for the exhaust temperature, an exhaust temperature sensor for detecting the exhaust temperature in the exhaust passage is provided in the exhaust passage in the vicinity of the exhaust purification catalyst 66, and the ECU 100 detects a signal related to the exhaust temperature from the exhaust temperature sensor. The exhaust temperature may be estimated as a control variable.

  Based on these control constants, the ECU 100 can adjust the opening of the EGR valve 74, that is, the flow rate of EGR gas guided to the intake passage. Further, the ECU 100 can adjust the coolant flow rate toward the exhaust-side cooling water passage 34, that is, the exhaust-side coolant flow rate, by controlling the flow rate distribution ratio of the flow dividing valve 44 based on the control variable described above. It has become.

  In the internal combustion engine 10 configured as described above, the negative pressure in the intake passage may be small depending on the operating state such as when the engine load is high, and the pressure (exhaust pressure) in the exhaust passage through which the EGR device 70 takes in the EGR gas. And the pressure in the intake passage through which EGR gas flows (intake pressure) is small, and even when the EGR valve 74 is opened and the EGR device 70 is operated, the EGR gas having a desired flow rate is guided to the intake passage. May be difficult.

  Therefore, in the internal combustion engine 10 according to the present embodiment, the ECU 100 causes the EGR device 70 to use the EGR gas when the operating state of the internal combustion engine 10 is in a predetermined region where the pressure difference between the exhaust pressure and the intake pressure is small. The exhaust pressure is raised by raising the exhaust gas temperature when the gas is introduced into the intake passage, which will be described below with reference to FIGS. FIG. 2 is a diagram for explaining an operation region of the internal combustion engine in which the ECU executes the exhaust gas temperature increase control. FIG. 3 is a flowchart showing exhaust temperature increase control executed by the ECU. FIG. 4 is a graph showing the exhaust temperature with respect to the engine speed and the engine load. FIG. 5 is a diagram for explaining a method of determining the lower limit value of the exhaust-side cooling water flow rate from the estimated exhaust temperature.

  The ECU 100 performs EGR when the operating state of the internal combustion engine 10 is in a predetermined region, for example, when the engine load is high and the engine rotational speed is in a low rotational speed range or a middle rotational speed range as indicated by hatching H in FIG. When the EGR gas is guided to the intake passage by the device 70, an exhaust temperature increase control routine shown in FIG. 3 is executed below.

  As shown in FIG. 3, the ECU 100 acquires various control variables related to the operating state of the internal combustion engine 10 in step S100. This control variable includes the engine speed of the internal combustion engine 10, the engine load, and the like.

  In step S102, the ECU 100 estimates the current exhaust-side cooling water flow rate. Specifically, the ECU 100 estimates the pumping flow rate of the cooling water pump 30 from the acquired engine rotation speed, and based on the cooling water flow rate and the opening degree (flow rate distribution ratio) of the diversion valve 44, the current exhaust-side cooling water flow rate. Can be estimated.

  In step S104, the ECU 100 estimates the current exhaust gas temperature based on the operating state (engine speed and engine load). Specifically, as shown in FIG. 4, the current exhaust gas temperature is estimated from a map showing the engine rotation speed, the engine load, and the exhaust gas temperature for these control variables.

  In step S106, the ECU 100 sets a lower limit value of the exhaust-side cooling water flow rate. Specifically, as shown in FIG. 5, the ECU 100 sets the lower limit of the exhaust-side cooling water flow rate so that the exhaust gas temperature becomes a preset upper limit value from the current exhaust gas temperature and the current exhaust-side cooling water flow rate. Set the value. Here, the upper limit value of the exhaust temperature is set in advance to a value that does not impair the function of the exhaust purification catalyst even if the exhaust gas at the exhaust temperature passes through the exhaust purification catalyst 66. The exhaust temperature with respect to the exhaust-side cooling water flow rate and the upper limit value of the exhaust temperature are obtained in advance by a matching experiment or the like, and are stored in the ROM of the ECU 100 as control constants.

  In step S110, the ECU 100 determines whether or not it is possible to reduce the exhaust-side cooling water flow rate so that the exhaust passage side of the engine body 20 can be in a weakly cooled state. Specifically, it is determined whether or not a value obtained by subtracting the lower limit value of the exhaust-side cooling water flow rate set in step S106 from the current exhaust-side cooling water flow rate estimated in step S102 is larger than a predetermined value. . The predetermined value is obtained in advance by a matching experiment or the like, and is stored in the ROM of the ECU 100 as a control constant. This predetermined value is set as a margin for the lower limit value of the exhaust-side coolant flow rate, and can be set to any value including zero.

  In step S110, when it is determined that the value obtained by subtracting the lower limit value of the set exhaust-side cooling water flow rate from the estimated exhaust-side cooling water flow rate is equal to or less than a predetermined value (No), the ECU 100 If the exhaust side cooling water flow rate is reduced by 44, it is determined that the exhaust temperature may exceed the upper limit value, and the reduction of the exhaust side cooling water flow rate is prohibited.

  On the other hand, when it is determined in step S110 that the value obtained by subtracting the lower limit value of the set exhaust-side cooling water flow rate from the estimated exhaust-side cooling water flow rate exceeds a predetermined value (Yes), the ECU 100 It is determined that the side cooling water flow rate can be reduced, and the process proceeds to step S112.

  In step S112, the ECU 100 newly sets the exhaust-side cooling water flow rate. Specifically, it is set to be equal to or lower than the lower limit value of the exhaust-side cooling water flow rate set in step S106.

  In step S114, the ECU 100 controls the flow distribution ratio of the diverter valve 44 to the exhaust side cooling water passage 34 to be reduced so that the new exhaust side cooling water flow rate set in step S112 is obtained. Reduce the side cooling water flow rate. The diversion valve 44 increases the EGR-side cooling water flow rate toward the EGR cooler 77 by the amount corresponding to the reduction of the exhaust-side cooling water flow rate.

  As described above, when the operating state of the internal combustion engine 10 is in a predetermined region, the ECU 100 opens the EGR valve 74 and guides the EGR gas to the intake passage by the EGR device 70. By reducing the water flow rate, the exhaust temperature of the exhaust gas flowing through the exhaust passage is raised. Since the exhaust pressure increases as the exhaust temperature increases, the pressure difference between the exhaust pressure and the intake pressure can be increased. As a result, even when the operating state of the internal combustion engine 10 is in a region where it is difficult to ensure a pressure difference between the exhaust pressure and the intake pressure (see FIG. 2), the flow rate of EGR gas guided to the intake passage in this region Can be further increased.

  In the present embodiment, the ECU 100 performs the above-described exhaust temperature increase control when the operating state of the internal combustion engine 10 is high when the engine load is high and the engine rotation speed is in a low rotation speed range or a medium rotation speed range. However, the operating state in which the exhaust temperature increase control is performed is not limited to this. In an operating state where the pressure difference between the exhaust pressure and the intake pressure is relatively small, or an operating state where an increase in the flow rate of the EGR gas is desired, it is preferable to perform the EGR gas when it is guided to the intake passage.

  As described above, the internal combustion engine 10 according to the present embodiment includes the EGR device 70 capable of guiding a part of the exhaust gas from the exhaust passage as EGR gas to the intake passage, and includes a plurality of cooling water passages 33, In the internal combustion engine 10 provided in the engine body 20, an exhaust side cooling water flow rate that is a flow rate of the cooling water flowing through the cooling water passage 34 closest to the exhaust passage among the cooling water passages 33, 34 of the plurality of paths is set. It has an adjustable flow rate adjusting means (a diversion valve 44), and an ECU 100 as a control means capable of controlling the EGR device 70 and the flow rate adjusting means 44.

  The ECU 100 as the control means has a function of increasing the exhaust temperature of the exhaust gas flowing through the exhaust passage when the EGR device 70 guides the EGR gas to the intake passage, so that the exhaust pressure increases according to the increase in the exhaust temperature. , And the flow rate of EGR gas can be increased by increasing the pressure difference between the intake pressure and the exhaust pressure.

  Further, the ECU 100 as the control means reduces the exhaust-side coolant flow rate by the flow rate adjusting means when the EGR device 70 guides the EGR gas to the intake passage when the operating state of the internal combustion engine 10 is in a predetermined region. Therefore, it is possible to increase the exhaust temperature, which is the temperature of the exhaust gas flowing through the exhaust passage, and to increase the exhaust pressure in accordance with the increase in the exhaust temperature, thereby increasing the pressure difference between the exhaust pressure and the intake pressure. be able to. Thereby, the flow rate of EGR gas guided to the intake passage can be increased.

  In the internal combustion engine 10, the EGR device 70 includes an EGR cooler 77 that cools the EGR gas, and the EGR cooler 77 has an EGR-side coolant flow rate that is a flow rate of coolant flowing through the EGR cooler 77 adjusted by a flow rate adjusting unit. Therefore, the ECU 100 as the control means decreases the exhaust-side cooling water flow rate and increases the EGR-side cooling water flow rate by the flow rate adjusting means (dividing valve 44). By cooling the EGR gas while increasing the exhaust pressure by reducing the exhaust-side cooling water flow rate, the EGR gas can be introduced into the intake passage with higher density.

  Further, in the internal combustion engine 10, the flow rate adjusting means includes an EGR side cooling water passage 35 through which the cooling water from the cooling water pump 30 flows through the EGR cooler 77, and an exhaust side cooling that is the cooling water passage closest to the exhaust passage. A diverter valve 44 for diverting to the water passage 34, and the ECU 100 as the control means controls the flow rate distribution ratio of the diverter valve 44 to increase the EGR side cooling water flow rate by reducing the exhaust side cooling water flow rate. It was. Reduction of the exhaust-side cooling water flow rate and increase of the EGR-side cooling water flow rate are realized with a simple configuration in which a diversion valve 44 for diverting cooling water is provided in the EGR-side cooling water passage 35 and the exhaust-side cooling water passage 34. can do.

  In the present embodiment, as the flow rate adjusting means, the diversion valve 44 for diverting the cooling water from the cooling water pump 30 to the EGR side cooling water passage 35 and the exhaust side cooling water passage 34 is provided. However, the embodiment is not limited to this. It suffices if the exhaust-side cooling water flow rate in the exhaust-side cooling water passage 34 can be reduced when the EGR gas is led to the intake passage. For example, a cooling water passage for communicating the exhaust-side cooling water passage 34 and the cooling water passage 42 upstream of the cooling water pump 30 and a valve capable of adjusting the flow rate of the cooling water passage are provided, and the EGR gas is used as the intake passage. When guiding, it is good also as what reduces the flow volume of exhaust side cooling water by opening the valve concerned.

[Embodiment 2]
The configuration of the internal combustion engine according to the present embodiment will be described with reference to FIG. FIG. 6 is a schematic diagram showing a schematic configuration of the internal combustion engine. In the internal combustion engine according to the present embodiment, an electric cooling water pump is provided instead of the mechanical cooling water pump, and an ECU as a control means of the internal combustion engine provides a cooling water flow rate pumped by the electric cooling water pump. Unlike the first embodiment, the details will be described below. In addition, about the structure substantially common with Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the internal combustion engine 10B according to this embodiment, a so-called electric cooling water pump (hereinafter simply referred to as “electric cooling water pump”) is used in order to pump the cooling water to the diversion valve 44 and the other cooling water passage 33. 30B is provided. The electric cooling water pump 30 </ b> B is driven by the electric motor and pumps the cooling water into the feed cooling water passage 31.

  Further, the internal combustion engine 10B is provided with an electronic control unit (hereinafter referred to as ECU) 100B as a control means for controlling this, that is, a control device for the internal combustion engine. The ECU 100B can control the opening degree of the EGR valve 74 of the EGR device 70 and the flow rate distribution ratio of the shunt valve 44, that is, the opening degree, according to the operating state of the internal combustion engine 10B.

  Further, the ECU 100B controls a cooling water flow rate (hereinafter referred to as a pressure feeding flow rate) that the electric cooling water pump 30B pumps to the feed cooling water passage 31 in accordance with the operating state of the internal combustion engine 10B (pressure feeding flow rate control means). have. In addition, the ECU 100B detects a signal related to the flow rate distribution ratio (opening) from the diversion valve 44, and constantly updates the flow rate distribution ratio as a control variable (learned value).

  The ECU 100B compares the flow rate distribution ratio (opening degree) instructed to the diversion valve 44 with the flow rate distribution ratio (opening degree) detected from the diversion valve 44, so that the diversion valve 44 is in accordance with its own instruction. It has a function (failure judgment means) for judging whether or not it is operating, that is, whether or not the shunt valve 44 is faulty.

  In the internal combustion engine 10B configured as described above, when the operating state of the internal combustion engine 10B is in a predetermined region (see FIG. 2), the ECU 100B opens the EGR valve 74 and the EGR device 70 performs EGR gas The flow distribution ratio to the exhaust-side cooling water passage 34 is reduced by the diversion valve 44 as a flow rate adjusting means so that the exhaust-side cooling water flow rate is reduced. Increase the pumping flow rate.

  As a result, the internal combustion engine 10B can increase the pressure difference between the exhaust pressure and the intake pressure by increasing the exhaust temperature by reducing the exhaust-side coolant flow rate, and the pumping flow rate of the electric coolant pump 30B can be increased. By the increase, the EGR side cooling water flow rate toward the EGR cooler 77 can be increased more than the reduced amount of the exhaust side cooling water flow rate, and the EGR gas flowing through the EGR cooler 77 can be further cooled and guided to the intake passage. .

  Further, the internal combustion engine 10B configured as described above reduces the exhaust temperature by increasing the exhaust-side coolant flow rate by the electric coolant pump 30B when the diversion valve 44 fails for some reason. This will be described below with reference to FIGS. FIG. 7 is a flowchart showing the exhaust temperature lowering control when the shunt valve fails. FIG. 8 is a diagram illustrating a method for estimating the exhaust-side cooling water flow rate from the opening degree at the time of failure of the shunt valve. FIG. 9 is a diagram for explaining a method of estimating the exhaust temperature and the lower limit value of the exhaust-side cooling water flow rate from the exhaust-side cooling water flow rate at the time of failure.

  As shown in FIG. 7, ECU 100B acquires various control variables related to the operating state of internal combustion engine 10B in step S200. This control variable includes the engine speed of the internal combustion engine 10B, the engine load, the flow rate of cooling water pumped by the electric cooling water pump 30B, and the like.

  In step S202, the ECU 100B determines whether or not the flow dividing valve 44 has failed. Specifically, by comparing the flow rate distribution ratio (opening degree) instructed to the diversion valve 44 with the flow rate distribution ratio (opening degree) detected from the diversion valve 44, the diversion valve 44 operates normally. It is determined whether it is malfunctioning or not. When it is determined that the valve is not broken (No), the process returns to step S200 again.

  On the other hand, when it is determined that the flow dividing valve 44 is broken (Yes), in step S204, the ECU 100B estimates the opening degree of the broken flow dividing valve 44, that is, the flow rate distribution ratio. This estimates the opening degree (flow rate distribution ratio) of the diversion valve 44 updated as a control variable immediately before the failure of the diversion valve 44 is determined as the current opening degree (flow rate distribution ratio).

  In step S206, the ECU 100B estimates the current exhaust-side coolant flow rate based on the estimated opening (flow rate distribution ratio) of the diversion valve 44 at the time of failure. Specifically, as shown in FIG. 8, the current exhaust-side cooling water flow rate is calculated based on the opening degree (flow rate distribution ratio) of the diversion valve 44 at the time of failure and the current pumping flow rate of the electric cooling water pump 30B. presume.

  In step S208, the ECU 100B estimates the current exhaust temperature of the exhaust gas flowing in the exhaust passage toward the exhaust purification catalyst 66 based on the estimated exhaust-side coolant flow rate and the operating state of the internal combustion engine 10B. To do.

  Then, in step S210, it is determined whether or not the estimated current exhaust temperature exceeds a preset upper limit value. The upper limit value of the exhaust temperature is set to a value that does not impair the function of the exhaust purification catalyst even when the exhaust gas at the exhaust temperature passes through the exhaust purification catalyst 66. This upper limit value is obtained in advance by a matching experiment or the like, and is stored in the ROM of the ECU 100B.

  As described above, in steps S204 to S210, the ECU 100B determines whether or not the current exhaust gas temperature exceeds the preset upper limit value when the flow dividing valve 44 is out of order (exhaust temperature determination means). )have. When it is determined that the exhaust temperature is equal to or lower than the upper limit value (No), the process returns to step S200 again.

  On the other hand, as shown in FIG. 9, when it is determined that the current exhaust gas temperature exceeds the preset upper limit value (Yes), in step S212, the ECU 100B determines that the exhaust gas temperature is based on the estimated exhaust gas temperature. The exhaust-side coolant flow rate is determined so as to be equal to or less than the upper limit value. Specifically, the lower limit value of the exhaust-side cooling water flow rate is estimated so that the exhaust gas temperature is equal to or lower than the upper limit value, and the exhaust-side cooling water flow rate is newly set to be equal to or higher than the lower limit value.

  In step S214, the ECU 100B controls the electric coolant pump 30B to increase the pumping flow rate so that the exhaust-side coolant flow rate newly set in step S212 is obtained. In this manner, the ECU 100B decreases the exhaust temperature of the exhaust gas flowing toward the exhaust purification catalyst 66 below a preset upper limit value by increasing the exhaust-side cooling water flow rate. Thereby, it can suppress that the exhaust purification catalyst 66 is exposed to high temperature exhaust gas, and a function is impaired.

  As described above, when the operating state of the internal combustion engine 10B is in a predetermined region, the ECU 100B causes the EGR device 70 to introduce the EGR gas into the intake passage by using the diversion valve 44 as a flow rate adjusting unit. The flow rate distribution ratio to the exhaust-side cooling water passage 34 is reduced so as to reduce the cooling water flow rate, and the pumping flow rate of the electric cooling water pump 30B, that is, the cooling water flow rate fed to the diversion valve 44 is increased. Further, the internal combustion engine 10B can increase the pressure difference between the exhaust pressure and the intake pressure by increasing the exhaust temperature by reducing the exhaust-side coolant flow rate, and increase the pumping flow rate of the electric coolant pump 30B. Thus, the EGR side cooling water flow rate toward the EGR cooler 77 is increased more than the reduced amount of the exhaust side cooling water flow rate, so that the EGR gas flowing through the EGR cooler 77 can be further cooled and guided to the intake passage.

  In the exhaust temperature lowering control routine (S200 to S214) according to the present embodiment, the flow rate of the exhaust side cooling water flowing through the exhaust side cooling water passage 34 is increased so that the exhaust temperature becomes equal to or lower than a preset upper limit value. However, the exhaust temperature is lowered (S212, S214), but the method of lowering the exhaust temperature is not limited to this. For example, the exhaust temperature may be lowered by increasing the amount of fuel supplied to supply the fuel into the cylinder of the internal combustion engine.

  As described above, in the internal combustion engine 10B according to the present embodiment, the ECU 100B serving as the control means is a pressure feed that is the coolant flow rate that the electric coolant pump 30B feeds at least toward the flow dividing valve 44 serving as the flow rate adjusting means. It is determined that the function for controlling the flow rate (pressure feed flow rate control unit), the function for determining whether or not the flow rate adjustment unit has failed (failure determination unit), and the shunt valve 44 (flow rate adjustment unit) have failed. The exhaust temperature of the exhaust gas flowing through the exhaust passage has a function (exhaust temperature determination means) for determining whether or not the exhaust temperature exceeds a preset upper limit value, and the exhaust temperature exceeds the upper limit value. If determined, the pumping flow rate of the electric cooling water pump 30B is increased.

  If the shunt valve 44 fails and the exhaust temperature exceeds a preset upper limit value, the pumping flow rate of the electric cooling water pump 30B is increased to increase the exhaust-side cooling water flow rate and lower the exhaust temperature. It is possible to prevent the exhaust temperature from exceeding the preset upper limit due to the failure of the flow dividing valve 44. This is useful for the internal combustion engine 10B in which the exhaust purification catalyst 66 is provided on the downstream side of the exhaust passage.

  In each of the above-described embodiments, the ECU (100; 100B) as the control means controls the exhaust-side coolant flow rate by the flow rate adjusting means (diversion valve 44) when the EGR device 70 guides the EGR gas to the intake passage. Although the function of increasing the exhaust temperature of the exhaust gas flowing through the exhaust passage by reducing (exhaust temperature increasing means) is provided, the method of increasing the exhaust temperature is not limited to this. For example, when the internal combustion engine is a gasoline engine, the ECU (100; 100B) can increase the exhaust gas temperature by retarding the ignition timing of the air-fuel mixture formed in the cylinder.

  As described above, the present invention is useful for an internal combustion engine including an EGR device capable of guiding a part of exhaust gas from an exhaust passage as EGR gas to an intake passage, and in particular, a plurality of cooling water passages are provided. It is suitable for an internal combustion engine provided in the engine body.

1 is a schematic diagram illustrating a schematic configuration of an internal combustion engine according to a first embodiment. FIG. 3 is a diagram illustrating an operating region of the internal combustion engine in which the control means (ECU) of the internal combustion engine according to the first embodiment executes exhaust gas temperature increase control. 3 is a flowchart showing exhaust temperature increase control executed by the control means (ECU) of the internal combustion engine according to the first embodiment. It is a figure which shows the exhaust temperature with respect to an engine speed and an engine load. It is a figure explaining the method of determining the lower limit of the exhaust side cooling water flow volume from the estimated present exhaust gas temperature. FIG. 3 is a schematic diagram showing a schematic configuration of an internal combustion engine according to a second embodiment. 6 is a flowchart showing exhaust temperature reduction control when a shunt valve fails in an internal combustion engine according to a second embodiment. In the internal combustion engine which concerns on Embodiment 2, it is a figure explaining the method of estimating an exhaust-side coolant flow rate from the opening degree at the time of the failure of a shunt valve. In the internal combustion engine which concerns on Embodiment 2, it is a figure explaining the method of estimating the exhaust gas temperature and the lower limit of the exhaust gas flow rate from the exhaust gas flow rate at the time of failure.

Explanation of symbols

10, 10B Internal combustion engine 20 Engine body 24 Throttle valve 26 Surge chamber (intake passage) of intake manifold
30 Mechanical cooling water pump 30B Electric cooling water pump 33 Other cooling water passage 34 Exhaust side cooling water passage 35 EGR side cooling water passage 40 Thermostat valve 44 Diverging valve (flow rate adjusting means, three-way valve)
60 Junction of exhaust manifold (exhaust passage)
66 Exhaust purification catalyst 70 EGR device 72 EGR passage 74 EGR valve 77 EGR cooler 80 Radiator 100, 100B Electronic control unit for internal combustion engine (ECU, control means, storage means, exhaust temperature increase means, pumping flow rate control means, failure determination means Exhaust temperature judgment means)

Claims (4)

An internal combustion engine comprising an EGR device capable of guiding a part of exhaust gas from an exhaust passage as EGR gas to an intake passage, and having a plurality of cooling water passages provided in the engine body,
A flow rate adjusting means capable of adjusting an exhaust side cooling water flow rate that is a flow rate of cooling water flowing through the cooling water passage closest to the exhaust passage among the cooling water passages of the plurality of paths;
Control means capable of controlling the EGR device and the flow rate adjusting means;
Have
The control means reduces the exhaust-side coolant flow rate by the flow rate adjusting means when the EGR gas is guided to the intake passage by the EGR device. The internal combustion engine according to claim 1,
The EGR device includes an EGR cooler that cools EGR gas, and the EGR cooler is configured such that the flow rate of the EGR-side cooling water, which is the flow rate of the coolant flowing through, is adjusted by the flow rate adjusting unit.
The control means reduces the exhaust-side cooling water flow rate and increases the EGR-side cooling water flow rate by the flow rate adjusting means. The internal combustion engine according to claim 2,
The flow rate adjusting means is a diversion valve that divides the cooling water from the cooling water pump into an EGR side cooling water passage that flows through the EGR cooler and an exhaust side cooling water passage that is the cooling water passage closest to the exhaust passage,
The control means controls the flow rate distribution ratio of the flow dividing valve to increase the EGR side cooling water flow rate by the amount of reducing the exhaust side cooling water flow rate. The internal combustion engine according to any one of claims 1 to 3,
The control means
A pumping flow rate control unit that controls a pumping flow rate that is a cooling water flow rate that the cooling water pump pumps at least toward the flow rate adjusting unit;
Failure determination means for determining whether or not the flow rate adjustment means is faulty;
An exhaust temperature determination means for determining whether or not the exhaust temperature of the exhaust gas flowing through the exhaust passage exceeds a preset upper limit value when it is determined that the flow rate adjustment means is malfunctioning;
Have
An internal combustion engine characterized by increasing the pumping flow rate of the cooling water pump when it is determined that the exhaust temperature exceeds the upper limit.

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