JP2009085011A - Exhaust gas recirculation device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas recirculation device for an internal combustion engine, neutralizing pH of intake gas by making exhaust gas rich in fuel to produce larger amount of NH<SB>3</SB>when pH of the intake gas is acid and preventing corrosion of intake system components. <P>SOLUTION: The exhaust gas recirculation device for the internal combustion engine 10 is provided with an intake pipe 32 and an exhaust pipe 41 provided in a main body of the engine 10; an EGR passage 52; an EGR valve 53; and a catalyst device 42 for eliminating harmful components in exhaust gas in the exhaust pipe 41. In the exhaust gas recirculation device for the internal combustion engine 10, pH of intake gas is detected. When the detected pH of the intake gas is a predetermined value or less and is on the acid side, an air fuel ratio of exhaust gas is controlled to the rich side based on the pH of the intake gas, and NH<SB>3</SB>is generated by progress of reduction reaction of NO<SB>X</SB>in the exhaust gas by a three way catalyst 43, so as to alkalify the exhaust gas. EGR gas including large amount of NH<SB>3</SB>is recirculated to the intake pipe 32 via the EGR passage 52, to adjust pH of the intake gas to become approximately neutral. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine that makes the pH of the intake gas of the intake system substantially neutral, prevents corrosion of the intake system and the exhaust gas recirculation system, and improves the durability of the intake system and the like.

Conventionally, a part of the exhaust (hereinafter referred to as “EGR gas”) discharged to the exhaust system of the internal combustion engine in order to reduce the amount of nitrogen oxide (NO _x ) in the exhaust of the internal combustion engine is referred to as the intake system of the internal combustion engine. There is known an exhaust gas recirculation device for an internal combustion engine that is introduced by exhaust gas recirculation (hereinafter referred to as “EGR”).

  For example, an exhaust gas recirculation device for an internal combustion engine as shown in FIG. 8 has been proposed as a conventional exhaust gas recirculation device for an engine. FIG. 8 is a diagram showing an example of the configuration of a conventional exhaust gas recirculation device for an internal combustion engine. As shown in FIG. 8, a conventional exhaust gas recirculation device 100 for an internal combustion engine sends an intake passage 102 for feeding intake gas (intake air) to an engine body 101 and exhaust gas discharged from the engine body 101. A supply exhaust passage 103 is connected (Patent Document 1).

  An air flow meter 104, a throttle valve 105, a supercharger 106, an intercooler 107, a surge tank 108, and fuel injection valves 109-1 and 109-2 are disposed in the intake passage 102. The supercharger 106 is mechanically driven by an engine output shaft via a transmission means such as a belt (not shown) and an electromagnetic clutch, for example.

  Further, the exhaust passage 103 is provided with a catalyst device 111 having a three-way catalyst 110 having at least a reduction function, such as a three-way catalyst 110 having both oxidation and reduction functions. The three-way catalyst 110 removes harmful components from the exhaust gas and exhausts the exhaust gas.

  Further, between the intake passage 102 and the exhaust passage 103, an exhaust gas recirculation passage (hereinafter referred to as an “EGR passage”) 112-1 that recirculates part of the exhaust gas (EGR gas) flowing through the exhaust passage 103 to the intake system. , 112-2. The exhaust passage 103 and the intake passage 102 on the upstream side of the catalyst device 111 are connected by the EGR passage 112-1, and the exhaust passage 103 and the intake passage 102 on the downstream side of the catalyst device 111 are connected by the EGR passage 112-2. In the EGR passages 112-1 and 112-2, an EGR valve 113 that operates in response to a signal from an electronic control unit (hereinafter referred to as “ECU”) (not shown) is installed, and according to the opening degree of the EGR valve 113. An appropriate amount of EGR gas is returned to the intake passage 102.

  In the exhaust gas recirculation device 100 of the conventional internal combustion engine, the exhaust gas is acidic on the upstream side of the catalyst device 111, and the exhaust gas is alkaline on the downstream side of the catalyst device 111, so that the EGR passages 112-1 and 112-2 A substantially neutral EGR gas having a pH value of about 7 obtained by adjusting and mixing these EGR gases was recirculated to the intake passage 102.

JP 07-324653 A

  However, the conventional exhaust gas purification device 100 for an internal combustion engine only adjusts the pH of the EGR gas and does not consider the pH of the intake gas, so that there is a problem that the pH of the intake gas tends to be acidic or alkaline. is there.

  That is, since the EGR gas is recirculated to the intake gas upstream of the EGR gas supercharger 106, the sulfur component contained in the soot in the EGR gas reacts with the water vapor warmed by the supercharger 106 in the supercharger 106. As a result, sulfuric acid is generated, the pH of the intake gas in the intake passage 102 becomes acidic, and metal parts made of aluminum-based metal such as the intake passage 102 of the intake system and the intercooler 107 are corroded and eventually melted. There is a problem that it may end up.

  The present invention has been made in view of the above problems, and when the pH of the intake gas is acidic, the exhaust gas is rich in fuel to produce more ammonia to neutralize the pH of the intake gas, and An object of the present invention is to provide an exhaust gas recirculation device for an internal combustion engine that prevents corrosion of system parts.

  In order to achieve the above object, an exhaust gas recirculation apparatus for an internal combustion engine according to the present invention includes an intake passage provided in an intake system of an engine body, an exhaust passage provided in the exhaust system, and the exhaust passage and the intake passage. And an exhaust gas recirculation passage for recirculating a part of the exhaust gas from the exhaust passage to the intake passage, and an exhaust gas recirculation passage provided in the exhaust gas recirculation passage for adjusting the flow rate of the exhaust gas flowing through the exhaust gas recirculation passage An exhaust gas recirculation control valve, and an exhaust gas recirculation device for an internal combustion engine having an exhaust gas purification device in which an exhaust gas purification catalyst for purifying harmful components in the exhaust gas is contained in the exhaust gas passage. When the pH of the flowing intake gas is on the acidic side, the air-fuel ratio of the exhaust gas is controlled based on the pH of the intake gas, and the pH of the intake gas is adjusted to be substantially neutral.

  In the exhaust gas recirculation device for an internal combustion engine according to the present invention, an intake pH estimating means for estimating the pH of the intake gas is provided, and the exhaust gas is determined based on the pH of the intake gas determined by the intake pH estimating means. The amount of ammonia in the exhaust gas that has passed through the exhaust purification catalyst is adjusted with the gas air-fuel ratio rich, and the exhaust gas that has passed through the exhaust purification catalyst is recirculated to the intake passage through the exhaust gas recirculation passage. The pH of the intake gas is approximately neutral.

  In the exhaust gas recirculation apparatus for an internal combustion engine according to the present invention, the intake pH estimation means is generated from hydrogen contained in the exhaust gas during fuel cut in the air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas. The pH of the intake gas is obtained based on an electromotive force.

  Further, in the exhaust gas recirculation device for an internal combustion engine according to the present invention, the intake pH estimation means sets the ignition timing retard amount in which the ignition retard is performed according to the knock magnitude of knocking caused by hydrogen generated during combustion. Based on this, the pH of the intake gas is obtained.

  According to the present invention, when the pH of the intake gas flowing through the intake passage is on the acidic side, the air-fuel ratio of the exhaust gas is controlled based on the pH of the intake gas so that the pH of the intake gas becomes substantially neutral. Since the adjustment is made, corrosion of intake system parts can be prevented.

  Further, according to the present invention, there is provided an intake pH estimating means for estimating the pH of the intake gas, and the exhaust gas purification is performed with the air-fuel ratio of the exhaust gas being rich based on the pH of the intake gas obtained by the intake pH estimating means. The amount of ammonia in the exhaust gas that has passed through the exhaust catalyst is adjusted, and the exhaust gas that has passed through the exhaust purification catalyst is recirculated to the intake passage through the exhaust gas recirculation passage so that the pH of the intake gas is substantially neutral. Therefore, corrosion of the intake system parts can be prevented more appropriately.

  In addition, according to the present invention, since the pH of the intake gas can be obtained based on the electromotive force generated from hydrogen contained in the exhaust gas during fuel cut, the pH of the intake gas becomes substantially neutral. In this way, the pH of the intake gas can be adjusted to prevent corrosion of intake system components.

  Further, according to the present invention, the pH of the intake gas can be obtained based on the ignition timing retard amount obtained by performing the ignition retard according to the knock magnitude of the knock caused by hydrogen generated during combustion. By adjusting the pH of the intake gas so that the pH of the intake gas becomes substantially neutral, corrosion of the intake system components can be prevented.

  Hereinafter, an example in which an exhaust gas recirculation apparatus for an internal combustion engine according to the present invention is applied to an engine system will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

FIG. 1 is a schematic configuration diagram showing an engine system to which an exhaust gas recirculation device for an internal combustion engine according to a first embodiment of the present invention is applied.
In the engine to which the exhaust gas purification apparatus for an internal combustion engine of the present embodiment is applied, as shown in FIG. 1, the engine 10 as the internal combustion engine is a cylinder injection type multi-cylinder in-line engine. In this engine 10, a cylinder head 12 is fastened on a cylinder block 11, and pistons 14 are fitted to a plurality of cylinder bores 13 formed in the cylinder block 11 so as to freely move up and down. A crankcase (not shown) is fastened to the lower part of the cylinder block 11, and a crankshaft 16 is rotatably supported in the crankcase. Each piston 14 is connected to the crankshaft 16 via a connecting rod 17. Has been.

  The combustion chamber 18 includes a cylinder block 11, a cylinder head 12, and a piston 14, and the combustion chamber 18 has a pent roof shape that is inclined so that the central portion of the upper portion (the lower surface of the cylinder head 12) is raised. Yes. An intake port 19 and an exhaust port 20 are formed on the upper portion of the combustion chamber 18, that is, the lower surface of the cylinder head 12, and the intake valve 19 and the exhaust valve 20 are opposed to the intake port 19 and the exhaust port 20. The lower end portions of 22 are respectively positioned. The intake valve 21 and the exhaust valve 22 are supported by the cylinder head 12 so as to be movable in the axial direction, and are urged and supported in a direction to close the intake port 19 and the exhaust port 20. An intake camshaft 23 and an exhaust camshaft 24 are rotatably supported by the cylinder head 12, and the intake cam 25 and the exhaust cam 26 are connected to upper ends of the intake valve 21 and the exhaust valve 22 via a roller rocker arm (not shown). In contact with the part.

  Therefore, when the intake camshaft 23 and the exhaust camshaft 24 rotate in synchronization with the engine 10, the intake cam 25 and the exhaust cam 26 operate a roller rocker arm (not shown), and the intake valve 21 and the exhaust valve 22 move up and down at a predetermined timing. By moving, the intake port 19 and the exhaust port 20 can be opened and closed, and the intake port 19 and the combustion chamber 18 and the combustion chamber 18 and the exhaust port 20 can communicate with each other.

  Further, the valve mechanism of the engine 10 is a variable intake / exhaust valve (VVT) 27, 28 that controls the intake valve 21 and the exhaust valve 22 at an optimal opening / closing timing according to the operating state. It has become. The intake / exhaust variable valve mechanisms 27 and 28 are configured, for example, by providing a VVT controller at the shaft ends of the intake camshaft 23 and the exhaust camshaft 24, and change the phase of the camsprocket with respect to the camshaft. Thus, the opening / closing timing of the intake valve 21 and the exhaust valve 22 can be advanced or retarded. In this case, the intake / exhaust variable valve mechanisms 27, 28 advance or retard the opening / closing timing with the operating angle (opening period) of the intake valve 21 and the exhaust valve 22 being constant. In addition, the intake camshaft 23 and the exhaust camshaft 24 are provided with cam position sensors 29 and 30 for detecting their rotational phases.

  A surge tank 31 is connected to the intake port 19 via an intake manifold (not shown). An intake pipe 32 is connected to the surge tank 31, and an air cleaner 33 is attached to an air intake port of the intake pipe 32. Yes. An electronic throttle device 36 having an intercooler 34 and a throttle valve 35 is provided on the downstream side of the air cleaner 33. An intake system passage composed of the intake port 19 and the intake pipe 32 is referred to as an intake passage.

  The cylinder head 12 is provided with an injector 38 that injects fuel from a high-pressure supply pump 37 supplied from a fuel tank (not shown) directly into the combustion chamber 18. The injector 38 is disposed on the intake port 19 side. It is located and inclined at a predetermined angle in the vertical direction. Further, the cylinder head 12 is provided with a spark plug 39 that is located above the combustion chamber 18 and ignites the air-fuel mixture. A port injection valve 40 for injecting fuel into the intake port is mounted.

On the other hand, an exhaust pipe 41 is connected to the exhaust port 20 via an exhaust manifold (not shown), and a catalyst device 42 is attached to the exhaust pipe 41. An exhaust system passage composed of the exhaust port 20 and the exhaust pipe 41 is referred to as an exhaust passage. The catalyst device 42 accommodates three-way catalysts 43 and 44 for purifying exhaust gas. These three-way catalysts 43 and 44 are three-way catalysts that purify harmful substances such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ) contained in the exhaust gas. In particular, when the air-fuel ratio is near the stoichiometric air-fuel ratio at a predetermined activation temperature or higher, harmful substances in the exhaust gas can be efficiently purified.

  The intake pipe 32 and the exhaust pipe 41 are provided with an electric assist turbocharger (MAT) 45. The electric assist turbocharger 45 is configured such that a compressor 45 a provided in the intake pipe 32 and a turbine 45 b provided in the exhaust pipe 41 are integrally connected by a drive shaft 45 c and are forcibly driven by a drive motor 46. can do. In addition, the intake pipe 32 on the downstream side of the compressor 45 a in the electrically assisted turbocharger 45 is cooled by the intercooler 34 with the intake gas that has been supercharged by the compressor 45 a and has risen in temperature.

  Further, the engine 10 is provided with a high pressure exhaust gas recirculation (EGR) device 51 that returns exhaust gas to the intake system. The EGR device 51 connects an intake pipe 32 and an exhaust pipe 41 to recirculate part of the exhaust gas to the intake system, and an engine provided in the EGR path 52. It comprises an exhaust gas recirculation control valve (EGR valve) 53 that is switched according to the operating state, and an EGR cooler 54 that is provided in the EGR passage 52 and cools the exhaust gas.

  A blow-by gas line 55 is provided in the cylinder block 11 of the engine 10 or a crankcase (not shown). For example, when the engine 11 is rotating, the piston 14 is lowered so that air pressure is generated in an oil pan (not shown). When the pressure is applied to the oil pan, the heated oil evaporates, and the so-called oil containing the heated oil is contained. Generate blow-by gas. Since this blow-by gas contains an acidic component, the interior of the engine 10 is rusted and the oil is deteriorated. Therefore, the blow-by gas is returned to the intake pipe 32 via the blow-by gas line 55 and burned in the engine 10, thereby improving the maintenance of the engine 10 and preventing the deterioration of the oil. Further, the blow-by gas line 55 may be connected to the air cleaner 33. Since the amount of blow-by gas increases as the rotational speed of the engine 10 increases, the blow-by gas may be supplied to the air cleaner 33 in addition to the intake pipe 32 and sucked into the air cleaner 33.

  The exhaust pipe 41 is provided with an exhaust bypass passage 61 that bypasses the turbine 45b. The amount of exhaust gas supplied to the exhaust bypass passage 61 is adjusted by controlling the opening and closing of the wastegate valve 62 provided in the exhaust bypass passage 61. The opening and closing of the waste gate valve 62 is controlled using an actuator 63. When the supercharging pressure increases, the waste gate valve 62 is opened to bypass the exhaust gas and control the amount of exhaust gas supplied to the bypass passage 61. ing. That is, the actuator 63 is controlled to the atmospheric pressure and the negative pressure by using the intake gas supplied from the surge tank 31 and the air cleaner 33 to the actuator 63 via the air bypass lines 64-1 to 64-3. 63 operates to control the opening and closing of the wastegate valve 62. The actuator 63 may be a driving device that generates power, such as a motor, an air cylinder, a hydraulic cylinder, a piezo (piezoelectric element), or the like. The intake air amount supplied from the air cleaner 33 and the surge tank 31 via the air bypass lines 64-1 to 64-3 is the same as the intake gas supplied via the intake air adjustment passages 65-1 to 65-3. And adjusted by the air bypass valve 66. The air bypass line 64-3 is provided with a pressure sensor 67 that detects the amount of intake air supplied to the actuator 63.

  In addition, an electronic control unit (ECU) 71 is mounted on the vehicle, and the ECU 71 can control the injector 38, the port injection valve 40, the spark plug 39, and the like.

  That is, an air flow sensor 72 is mounted on the upstream side of the intake pipe 32, and the measured intake air amount is output to the ECU 71. An intake air temperature sensor 73 is mounted on the downstream side of the intercooler 34 of the intake pipe 32 and outputs the measured intake air amount and intake air temperature to the ECU 71. The electronic throttle device 36 is provided with a throttle position sensor 74 and outputs the current throttle opening to the ECU 71. Further, the crank angle sensor 75 outputs the detected crank angle of each cylinder to the ECU 71, and the ECU 71 determines each stroke of intake, compression, expansion (explosion), and exhaust in each cylinder based on the detected crank angle. At the same time, the engine speed is calculated.

  In addition, vacuum sensors 76-1 and 76-2 are mounted on the downstream side of the intercooler 34 of the intake pipe 32 and in the surge tank 31, and the negative pressure of the intake gas is measured and output to the ECU 71. .

  The cylinder block 11 is provided with a water temperature sensor 77 for detecting the engine coolant temperature, and outputs the detected engine coolant temperature to the ECU 71. In addition, the cylinder block 11 is provided with a knock sensor 78 that measures the knock strength of the knock generated during combustion, and outputs the detected knock strength to the ECU 71.

  Accordingly, the ECU 71 determines the fuel injection amount, the injection timing based on the detected intake air amount, intake air temperature, throttle opening (or accelerator opening), engine speed, engine cooling water temperature, knock strength, and other engine operating conditions. The ignition timing is determined.

  The ECU 71 can control the intake / exhaust variable valve mechanisms 27 and 28 based on the engine operating state, and is controlled according to the engine operating state.

Further, a temperature sensor (not shown) for detecting the catalyst bed temperature of the three-way catalyst 43, 44 is provided in the catalyst device 42. Further, on the upstream side of the catalyst device 42, an air-fuel ratio sensor (hereinafter referred to as “A / F sensor”) 79 for detecting an exhaust gas air-fuel ratio and a three-way catalyst 43, 44 are disposed in the exhaust gas. An oxygen sensor (hereinafter referred to as “O ₂ sensor”) 80 for detecting the amount of oxygen is attached.

The A / F sensor 79 detects the exhaust gas air-fuel ratio of the exhaust gas before being introduced into the three-way catalysts 43 and 44 out of the exhaust gas exhausted from the combustion chamber 18 to the exhaust port 20, and the detected air-fuel ratio is detected. Is output to the ECU 71. The air-fuel ratio (estimated air-fuel ratio) detected by the A / F sensor 79 is used for feedback control of the air-fuel ratio (theoretical air-fuel ratio) of the mixed gas composed of intake air and fuel. That is, the A / F sensor 79 detects the exhaust air / fuel ratio from the rich region to the lean region from the oxygen concentration and the unburned gas concentration in the exhaust gas, and feeds back this to the ECU 71 to correct the fuel injection amount. Thus, the combustion in the combustion chamber 18 can be controlled to an optimum combustion state that matches the operating state. The O ₂ sensor 80 detects the oxygen concentration of the exhaust gas that has passed through the three-way catalyst 43, and outputs the detected oxygen concentration to the ECU 71.

[Operation control method]
Next, an operation control method in the engine system to which the exhaust gas recirculation apparatus for the internal combustion engine of the present embodiment is applied will be specifically described with reference to FIG. 1 based on the flowchart of FIG.
FIG. 2 is a flowchart showing an operation control method in the engine system to which the exhaust gas recirculation device for the internal combustion engine according to the present embodiment is applied. The following control is performed by the ECU 71.
As shown in FIG. 2, the operation control method in the engine system to which the exhaust gas recirculation device for the internal combustion engine according to the present embodiment is applied, detects the pH of the intake gas, and when the pH of the intake gas is equal to or lower than a predetermined value, By controlling the air-fuel ratio of the exhaust gas to the rich side, the reduction reaction of NO _{x in} the exhaust gas proceeds by the three-way catalyst 43 to generate NH ₃ so that the pH in the exhaust gas becomes the alkali side, By controlling the opening degree of the EGR valve 53, the exhaust gas containing a large amount of NH ₃ is recirculated to the intake pipe 32, and the pH of the intake gas is adjusted so that the pH of the intake gas becomes substantially neutral.

  Further, in the present invention, “substantially neutral” means a pH at which the pH value of the intake gas is about 7, and the intake system components provided in the intake system are hardly corroded. When the pH value is almost neutral when the pH value is around 7, none of the metals corrodes, but the aluminum-based metal becomes alkaline when the pH value is larger than about 8, for example, or the pH value is smaller than about 4, for example. If it becomes acidic, it tends to corrode. Therefore, as a neutrality, the pH value is preferably in the range of 6 to 8, and more preferably in the range of 6.5 to 7.5.

That is, the operation control method in the engine system to which the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment is applied includes an intake pH detection step (step S11) for detecting the pH of the intake gas, and whether the pH of the intake air is a predetermined value or less. From the step of determining (step S12), the air-fuel ratio rich control step (step S13) for controlling the air-fuel ratio richly, and the EGR valve opening degree control step (step S14) for controlling the opening degree of the EGR valve 53 Become.
Further, a specific process of the intake pH detection process of detecting the pH of the intake gas in step S11 is performed based on the flowcharts of FIGS. 3 and 5 described later.

  First, in FIG. 2, in step S11, the pH of the intake gas is detected. FIG. 3 shows a specific process for detecting the pH of the intake gas in step S11.

[Detection of first intake pH]
FIG. 3 is a flowchart specifically showing a first intake pH detection step for detecting the pH of the intake gas.
As shown in FIG. 3, the pH of the first intake gas is detected by determining whether the F / C continuation time is equal to or greater than a predetermined value (step S21), and by using the A / F sensor 79, It includes a step of detecting and storing an electromotive force generated by the reaction of hydrogen (step S22), and an intake pH estimating step of estimating the pH of the intake gas from the stored electromotive force (step S23).

  First, in FIG. 3, in step S21, it is determined whether or not the fuel cut (F / C) continuation time is equal to or greater than a predetermined value. In order to detect the pH of the intake gas, it is confirmed whether or not combustion is performed. As a result of the determination in step S21, when it is determined that the F / C continuation time is equal to or longer than the predetermined value (step S21: Yes), that is, when it is determined that combustion is not performed, the process proceeds to step S22.

In step S22, the A / F sensor 79 detects and stores an electromotive force generated by the reaction of hydrogen in the intake gas. When hydrogen (H ₂ ) in the intake gas reacts with oxygen (O ₂ ) in the atmosphere in the A / F sensor 79 on the surface of the A / F sensor 79, an electromotive force is generated. Therefore, the A / F sensor 79 detects and stores the electromotive force generated by the reaction of hydrogen in the intake gas. And after detecting an electromotive force, it transfers to step S23.

  In step S23, the pH of the intake gas is estimated from the stored electromotive force of hydrogen. In order to estimate the pH of the intake gas from the electromotive force of hydrogen detected by the A / F sensor 79, it is determined with reference to a predetermined map.

The relationship between the electromotive force of hydrogen detected by the A / F sensor 79 and pH is shown in FIG.
FIG. 4 is a diagram showing the relationship between the electromotive force of hydrogen detected by the A / F sensor and the pH.
As shown in FIG. 4, when the pH falls from a neutral (7.0) state to an acidic state such as 5.5, the electromotive force does not change greatly, but the pH is, for example, 3.5 to When the voltage drops to about 5.5, it can be confirmed that the electromotive force changes greatly. In addition, when the pH is, for example, 3.5 or less, the electromotive force does not change greatly, and when the pH is, for example, about 2.0, the electromotive force is the maximum value.

  Therefore, the pH of the intake gas can be estimated from the detected hydrogen electromotive force based on a map showing the relationship between a predetermined hydrogen electromotive force and pH as shown in FIG.

  On the other hand, as a result of the determination in step S21 in FIG. 3, when the F / C continuation time is determined to be equal to or less than the predetermined value (step S21: No), the control of the first suction detection process is terminated.

  And it transfers to step S12 shown in FIG. 2, and it is determined whether pH of intake gas is below a predetermined value. Here, the predetermined value refers to a value indicating whether or not the A / F sensor 79 can detect hydrogen. As a result of the determination in step S12, when it is determined that the pH of the intake gas is equal to or lower than the predetermined value (step S12: Yes), the intake pipe and the like provided in the intake system are dissolved because the acidity of the intake gas is strong. Since there is a possibility, the process proceeds to step S13 in order to control the air-fuel ratio.

In step S13, the air-fuel ratio of the exhaust gas is controlled to be rich. The exhaust gas discharged from the combustion chamber of the engine contains NO _x and SO _x , and since this NO _x and SO _x are weakly acidic, the exhaust gas discharged from the combustion chamber becomes acidic. ing. Further, when the exhaust gas passes through the three-way catalyst 43 provided in the exhaust pipe 41, NO _x in the exhaust gas is reduced and a part thereof becomes alkaline ammonia (NH ₃ ), and SO _x is oxidized. To SO ₃ . For this reason, the pH of the exhaust gas after passing through the three-way catalyst 43 is shifted to the alkali side due to NH _{3 in} the exhaust gas. Further, not only a three-way catalyst but also a catalyst having at least a reducing function, for example, an NH ₃ purification catalyst is provided. Similarly, when exhaust gas passes through the catalyst, NH ₃ is generated and the pH of the exhaust gas is set to the alkali side. Shift.

Accordingly, the air-fuel ratio of the exhaust gas is set to the rich side, and the NH ₃ is generated by proceeding the reduction reaction of NO _{x in} the exhaust gas by the three-way catalyst 43 so that the pH in the exhaust gas becomes the alkali side. . At this time, the ratio at which the air-fuel ratio of the exhaust gas is rich is determined by the pH of the intake gas detected in step S11. In step S13, the air-fuel ratio of the exhaust gas is made rich, and a large amount of NH ₃ is contained in the exhaust gas after passing through the three-way catalyst 43. Then, the process proceeds to step 14.

In step S14, the opening degree of the EGR valve 53 is controlled. Specifically, by opening the EGR valve 53, a part of the exhaust gas containing a large amount of NH ₃ after passing through the three-way catalyst 43 is recirculated to the intake pipe 32 as EGR gas. Further, when the EGR valve 53 is opened, the flow rate of the EGR gas to be recirculated to the intake gas is adjusted by adjusting the opening degree of the EGR valve 53. Thereby, since the EGR gas containing NH ₃ can be mixed in the acidic intake gas, the pH of the intake gas can be made substantially neutral. As a result, corrosion of intake system components such as the intercooler 34 provided in the intake pipe 32 can be prevented.

  The blow-by gas generated in the engine 10 is returned to the intake pipe 32 through the blow-by gas line 55 as described above. Since this blow-by gas contains an acidic component, the pH of the intake gas may be further lowered by returning the blow-by gas to the intake pipe 32 via the blow-by gas line 55.

In this case, in the exhaust gas recirculation device 100 of the conventional internal combustion engine as shown in FIG. 8, the EGR gas is made substantially neutral and recirculated to the intake passage 102. Therefore, the EGR made substantially neutral by inflow of blow-by gas. There are cases where the pH of the intake gas does not become substantially neutral even when the gas is allowed to flow into the intake gas. On the other hand, in the exhaust gas recirculation apparatus for an internal combustion engine of the present invention, a part of the exhaust gas containing NH ₃ necessary for the pH of the intake gas to be substantially neutral is recirculated to the intake pipe 32 as EGR gas. Yes. For this reason, the exhaust gas recirculation device for an internal combustion engine of the present invention can make the pH of the intake gas substantially neutral without being affected by blow-by gas.

  And in step S14, after making pH of intake gas substantially neutral, operation control is ended.

  On the other hand, as a result of the determination in step S12, if the pH of the exhaust gas is determined to be equal to or higher than a predetermined value (step S12: No), the intake gas is not acidic and the intake pipe provided in the intake system is Since the possibility of being dissolved is low, the operation control is terminated while maintaining the state as it is.

  In step S11, the intake pH is detected by detecting the electromotive force generated by the reaction of hydrogen by the A / F sensor 79, as shown in FIG. However, the present invention is not limited to this, and the pH of the intake gas may be estimated using the knock sensor 78. For example, when the hydrogen is added as fuel in a hydrogen engine, the ignition timing is retarded according to the knock intensity when knocking occurs in the cylinder block 11, and the amount of intake gas is determined from the ignition timing retard amount at this time. The pH may be estimated.

  Next, a specific process for estimating the pH of the intake gas from the ignition timing retardation amount and detecting the pH of the intake gas in step S11 is shown in FIG.

[Detection of second intake pH]
FIG. 5 is a flowchart specifically showing a second intake pH detection step for detecting the pH of the intake gas.
As shown in FIG. 5, the pH of the second intake gas is detected by determining whether or not the engine load is equal to or lower than a predetermined value (step S31) and delaying the ignition timing due to occurrence of knocking in the cylinder block 11. From the step of detecting and storing the ignition timing retard amount when the keratinization is executed (step S32), and the intake pH estimating step of estimating the pH of the intake gas from the stored ignition timing retard amount (step S33). Become.

  First, in FIG. 5, in step S31, it is determined whether or not the engine load is a predetermined value or less. Specifically, for example, in a hydrogen engine, knocking occurs in the cylinder block 11 when hydrogen is added as fuel, so that the ignition timing is retarded according to the knock intensity. Therefore, it is determined whether or not knocking has occurred by the knock sensor 78, and it is determined whether or not it is a retard amount at an ignition timing with a margin that does not cause knocking with respect to the knock limit at which knocking occurs as a predetermined value. Judgment can be made. As a result of the determination in step S31, when the engine load is determined to be equal to or less than a predetermined value (step S31: Yes), it is a retard amount at an ignition timing with a margin that does not cause knocking, and a region where knocking does not occur And the process proceeds to step S32.

  In step S32, the ignition timing retard amount when the ignition timing is retarded due to the occurrence of knocking in the cylinder block 11 is detected and stored. Specifically, since knocking occurs due to the generation of hydrogen during combustion, the ignition retardation is implemented according to the knock intensity. Therefore, the ignition timing retard amount obtained by executing the ignition retard with respect to knocking caused by the generation of hydrogen is detected and stored. And after memorize | storing ignition timing retard amount, it transfers to step S33.

  In step S33, the pH of the intake gas is estimated from the stored ignition timing retard amount. In order to estimate the pH of the intake gas from the ignition timing retardation amount, it is determined with reference to a predetermined map.

Next, the relationship between the ignition timing retardation amount and the pH is shown in FIG.
FIG. 6 is a relationship diagram showing the relationship between the ignition timing retardation amount and the pH.
As shown in FIG. 6, when the ignition timing retardation amount is 0.0, the pH of the intake gas is in a neutral (7.0) state, and the pH of the intake gas increases as the ignition timing retardation amount increases. Was confirmed to fall.

  Therefore, the pH of the intake gas can be estimated from the ignition timing retardation amount detected based on the map showing the relationship between the predetermined ignition timing retardation amount and pH as shown in FIG.

  On the other hand, if it is determined in step S31 in FIG. 5 that the engine load is greater than or equal to the predetermined value (step S31: No), it is determined that the region is where knocking has occurred, and the second intake pH is determined. The control of the detection process is terminated.

  Then, after the control of the second intake pH detection step is completed, the routine proceeds to step S12 shown in FIG. 2, and as described above, it is determined whether or not the pH of the intake gas is not more than a predetermined value, and the determination of step S12 is performed. As a result, if the pH of the intake gas is determined to be equal to or lower than the predetermined value (step S12: Yes), the intake pipe or the like provided in the intake system may be dissolved due to the strong acidity of the intake gas. Then, the process proceeds to step S13 in order to control the air-fuel ratio.

In step S13, the air-fuel ratio of the exhaust gas is controlled to be rich, and the reduction reaction of NO _{x in} the exhaust gas is advanced by the three-way catalyst 43, so that NH _{3 is} contained in the exhaust gas after passing through the three-way catalyst 43. After a large amount is contained, the process proceeds to step 14.

In step S14, the opening degree of the EGR valve 53 is controlled to adjust the flow rate of the EGR gas that recirculates a part of the exhaust gas containing a large amount of NH ₃ to the intake pipe 32 as EGR gas. Thereby, since the EGR gas containing NH ₃ can be mixed in the acidic intake gas, the pH of the intake gas can be made substantially neutral. As a result, corrosion of intake system components such as the intercooler 34 provided in the intake pipe 32 can be prevented.

As described above, according to the engine system to which the exhaust gas purification apparatus for an internal combustion engine according to the embodiment of the present invention is applied, the exhaust gas is made rich when the pH of the intake gas is acidic by this series of control methods. By generating ₃ and mixing the exhaust gas made alkaline into the intake gas, the intake gas can be made neutral. Thereby, corrosion of an intake passage and intake system parts can be prevented.

An example in which the exhaust gas recirculation apparatus for an internal combustion engine according to the second embodiment of the present invention is applied to an engine system will be described with reference to FIG.
FIG. 7 is a schematic view schematically showing the configuration of an engine system of an exhaust gas recirculation apparatus for an internal combustion engine according to an embodiment of the present invention.
The engine system to which the exhaust gas recirculation device for the internal combustion engine according to the present embodiment is applied has the same configuration as that of the engine system to which the exhaust gas recirculation device for the internal combustion engine according to the first embodiment is applied. The same reference numerals are used for the same configuration as the configuration of the engine system to which the exhaust gas recirculation device for the internal combustion engine is applied, and the description thereof is omitted.
As shown in FIG. 7, the engine system to which the exhaust gas purification apparatus for an internal combustion engine according to the embodiment of the present invention is applied is provided with a dummy member 81 in the intake passage 32. As the material of the dummy member 81, for example, aluminum or stainless steel is used.

By providing the dummy member 81 in the intake passage 32, the dummy member 81 is corroded by an acidic component in the intake gas and a large amount of hydrogen is generated, thereby increasing the amount of hydrogen reaction in the A / F sensor 79. Therefore, the electromotive force generated when hydrogen reacts with oxygen (O ₂ ) in the air on the atmosphere side supplied to the A / F sensor 79 by the A / F sensor 79 can be increased, and the electromotive force of hydrogen Detection performance can be increased. As a result, it is possible to improve the pH detection performance of the intake gas.

  Even when the ignition timing is retarded according to the knock magnitude when knocking occurs in the cylinder block 11 and the pH of the intake gas is estimated from the obtained ignition timing retardation amount, Since a large amount of hydrogen can be added, the detection performance of knocking generated in the cylinder block 11 by the knock sensor 78 can be increased by increasing the amount of generated hydrogen. As a result, it is possible to improve the pH detection performance of the intake gas.

  Therefore, according to the engine system to which the exhaust gas recirculation device for the internal combustion engine according to the present embodiment is applied, the dummy member 81 is provided in the intake passage 32, and the dummy member 81 is corroded by the intake gas, thereby reducing the amount of hydrogen in the intake gas. Therefore, it is possible to improve the detection performance of the pH of the intake gas by increasing the detection performance of hydrogen electromotive force by the A / F sensor 79 or by increasing the detection performance of knocking by the knock sensor 78. it can. As a result, it is possible to improve the corrosion prevention of the intake passage 32 and the intake system components.

As described above, the exhaust gas recirculation device for an internal combustion engine according to the present invention generates NH ₃ by making the exhaust gas rich when the pH of the intake gas is acidic, and makes the exhaust gas alkaline based on the pH of the intake gas. By mixing the gas into the intake gas and making the intake gas substantially neutral, it is intended to improve the corrosion prevention of the intake system components, and is suitable for use in any type of internal combustion engine.

1 is a schematic configuration diagram illustrating an engine system to which an exhaust gas recirculation device for an internal combustion engine according to a first embodiment of the present invention is applied. It is a flowchart which shows the operation control method in the engine system to which the exhaust gas recirculation apparatus for the internal combustion engine according to the present embodiment is applied. 5 is a flowchart specifically showing a first intake pH detection step. It is a figure which shows the relationship between the electromotive force of hydrogen detected by the A / F sensor, and pH. It is a flowchart showing a 2nd intake pH detection process concretely. It is a relationship figure which shows the relationship between ignition timing retard amount and pH. It is a schematic block diagram showing the engine system with which the exhaust gas recirculation apparatus of the internal combustion engine which concerns on Example 2 of this invention was applied. It is a figure which shows an example of a structure of the exhaust-gas recirculation apparatus of the conventional internal combustion engine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 11 Cylinder block 12 Cylinder head 13 Cylinder bore 14 Piston 16 Crankshaft 17 Connecting rod 18 Combustion chamber 19 Intake port 20 Exhaust port 21 Intake valve 22 Exhaust valve 23 Intake camshaft 24 Exhaust camshaft 25 Intake cam 26 Exhaust cam 27 Intake possible Variable valve mechanism 28 Exhaust variable valve mechanism 29, 30 Cam position sensor 31 Surge tank 32 Intake pipe 33 Air cleaner 34 Intercooler 35 Throttle valve 36 Electronic throttle device 37 High pressure supply pump 38 Injector 39 Spark plug 40 Port injection valve 41 Exhaust pipe 42 Catalyst device 43, 44 Three-way catalyst 45 Electric assist turbocharger 45a Compressor 45b Turbine 45c Drive shaft 46 Drive motor 51 High pressure exhaust Recirculation (EGR) device 52 exhaust gas recirculation passage (EGR passage)
53 Exhaust gas recirculation control valve (EGR valve)
54 EGR cooler 55 Blow-by gas line 61 Exhaust bypass passage 62 Waste gate valve 63 Actuator 64-1 to 64-3 Air bypass line 65-1 to 65-3 Intake adjustment passage 66 Air bypass valve 67 Pressure sensor 71 Electronic control unit (ECU) )
72 Airflow sensor 73 Intake air temperature sensor 74 Throttle position sensor 75 Crank angle sensor 76-1, 76-2 Vacuum sensor 77 Water temperature sensor 78 Knock sensor 79 Air-fuel ratio sensor (A / F sensor)
80 Oxygen sensor 81 Dummy member

Claims (4)

An intake passage provided in the intake system of the engine body and an exhaust passage provided in the exhaust system;
An exhaust gas recirculation passage that connects between the exhaust passage and the intake passage, and recirculates part of the exhaust gas from the exhaust passage to the intake passage;
An exhaust gas recirculation control valve which is provided in the exhaust gas recirculation passage and adjusts the flow rate of the exhaust gas flowing through the exhaust gas recirculation passage;
In the exhaust gas recirculation device for an internal combustion engine, the exhaust passage having a gas purification device in which an exhaust purification catalyst that purifies harmful components in the exhaust gas is accommodated in the exhaust passage,
When the pH of the intake gas flowing through the intake passage is on the acidic side, the air-fuel ratio of the exhaust gas is controlled based on the pH of the intake gas, and the pH of the intake gas is adjusted to be substantially neutral. An exhaust gas recirculation device for an internal combustion combustor. In claim 1,
Intake pH estimating means for estimating the pH of the intake gas is provided,
Based on the pH of the intake gas determined by the intake pH estimating means, the amount of ammonia in the exhaust gas that has passed through the exhaust purification catalyst is adjusted by making the air-fuel ratio of the exhaust gas rich, and the exhaust purification catalyst An exhaust gas recirculation device for an internal combustion fueler, wherein the exhaust gas that has passed through the exhaust gas is recirculated to the intake passage through the exhaust gas recirculation passage so that the pH of the intake gas is substantially neutral. In claim 2,
The intake pH estimation means obtains the pH of the intake gas based on an electromotive force generated from hydrogen contained in the exhaust gas during fuel cut in an air-fuel ratio detection means for detecting an air-fuel ratio of the exhaust gas. An exhaust gas recirculation device for an internal combustion combustor. In claim 2,
An internal combustion engine characterized in that the intake pH estimation means obtains the pH of the intake gas based on an ignition timing retard amount obtained by performing an ignition retard according to a knock magnitude of knocking caused by hydrogen generated during combustion. Exhaust gas recirculation device for combustors.

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