JPH09324706A - Exhaust gas re-circulation device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the durability of an engine while carrying out EGR gas supply operation at the engine cooling time. SOLUTION: EGR gas supply operation is carried out by communicating an exhaust manifold 7 with the intake duct 4 of the downstream of a throttle valve 6 each other by the EGR passage 10. A neutralizer feeder 12 for injecting the neutralizer for neutrilizing a sulfuric acid in the intake duct 4 is provided. When the EGR gas supply operation is carried out when an engine cooling water temperature is lower than a set water temperature decided in advance, the neutralizer is injected from the neutralizer feeder 12. This neutralizer neutralizes the sulfuric acid produced in a combustion room when EGR gas supply operation is carried out at the engine cooling time and thereby, the corrosion of a cylinder bore inner wall surface, piston ring or piston is obstructed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas recirculation system for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, an engine exhaust passage and an engine intake passage are connected to each other by an EGR gas passage, and an E gas is introduced into a combustion chamber.
An exhaust gas recirculation device for an internal combustion engine that supplies GR gas is known. Thus, when the EGR gas is supplied into the combustion chamber, the nitrogen oxides (N
O _X) amount is reduced.

By the way, when the engine is cold, the temperature of the catalyst connected to the exhaust passage may not rise to its activation temperature. In this case, even if the exhaust gas is guided to the catalyst, the nitrogen oxides in the exhaust gas are removed. It cannot be purified well. Therefore, if the EGR gas is supplied into the combustion chamber even when the engine is cold, the amount of nitrogen oxides discharged into the exhaust passage when the engine is cold can be reduced.

However, the wall temperature of the cylinder bore is relatively low when the engine is cold, and if this wall temperature becomes lower than the dew point with respect to the pressure in the combustion chamber during the intake stroke, E
Moisture in the GR gas and sulfuric acid vapor are condensed to form sulfuric acid mist, which corrodes the inner wall surface of the cylinder bore. That is, when the fuel contains sulfur, sulfurous acid gas (SO ₂ ) is generated from this sulfur and is discharged into the exhaust passage. Further, part of the sulfurous acid gas is further oxidized to generate sulfuric acid (H ₂ SO ₄ ) or anhydrous sulfuric acid (SO ₃ ). Therefore, in this case, when the EGR gas supply operation is performed, sulfuric acid vapor may flow into the combustion chamber. So E
An electric heating element is placed in the GR gas passage to enable EGR when the engine is cold.
An exhaust gas recirculation device is known in which the EGR gas flowing in the gas passage is heated by the electric heating element (see Japanese Utility Model Laid-Open No. 61-69457). In this exhaust gas recirculation device, the EGR gas is heated when the engine is cold to suppress condensation of water and sulfuric acid vapor in the EGR gas,
This prevents the inner wall surface of the cylinder bore from being corroded as much as possible.

[0005]

However, in order to suppress the condensation of water and sulfuric acid vapor when the engine is cold, EGR is performed.
The amount of heat required to heat the gas is enormous, and thus it is difficult to suppress the generation of sulfuric acid mist.
However, the sulfuric acid condensed on the inner wall surface of the cylinder bore has a high hydrogen ion concentration, so that the inner wall surface of the cylinder bore is remarkably corroded, and the lubricating oil film is ruptured to cause cohesive wear.

[0006]

In order to solve the above problems, according to the present invention, there is provided an exhaust gas recirculation system for an internal combustion engine, comprising an EGR gas passage for connecting an engine exhaust passage and an engine intake passage to each other. When the EGR gas is supplied while the engine is cold, the engine intake passage, the combustion chamber, or E
The GR gas passage is provided with a neutralizer supplying means for supplying a neutralizer for neutralizing sulfuric acid. That is, the sulfuric acid produced in the combustion chamber by performing the EGR gas supply action while the engine is cold is neutralized by the neutralizing agent, so that the inner wall surface of the cylinder bore is prevented from being significantly corroded.

[0007]

FIG. 1 shows a case where the present invention is applied to a diesel engine. However, the invention can also be applied to gasoline spark ignition engines. Referring to FIG. 1, the engine body 1 includes four cylinders 1a.
Each cylinder 1a is connected to a common surge tank 3 via a corresponding intake branch pipe 2, and the surge tank 3 is connected to an air cleaner 5 via an intake duct 4. Inside the intake duct 4, there is arranged a throttle valve 6 whose opening degree increases as the depression amount of an accelerator pedal (not shown) increases. On the other hand, each cylinder 1a is connected via a common exhaust manifold 7 to, for example, a catalytic converter 9 containing a three-way catalyst 8.

In the EGR gas passage 10 that connects the collecting portion of the exhaust manifold 7 and the intake duct 4 downstream of the throttle valve 6 to each other, an E flowing in the EGR gas passage 10 is provided.
An EGR gas control valve 11 for controlling the amount of GR gas is arranged. The EGR gas control valve 11 is controlled based on the output signal from the electronic control unit 20. When the EGR gas supply operation should be performed, the EGR gas control valve 11 is opened. As a result, the EGR gas is supplied into the intake duct 4 via the EGR gas passage 10, and then each cylinder 1
The air is sucked into the combustion chamber of a together with air, and thus the EGR gas supply action is performed. On the other hand, when the EGR gas supply action should be stopped, the EGR gas control valve 11 is closed.

Further, the internal combustion engine of FIG. 1 is provided with a neutralizer supplying device 12. The neutralizer supply device 12 includes a neutralizer tank 13, a neutralizer injection nozzle 14 for injecting the neutralizer into the intake duct 4 downstream of the outlet of the EGR gas passage 10, and the neutralizer tank. A neutralizer pump 15 for supplying the neutralizer in 13 to the neutralizer injection nozzle 14. As will be described later, the neutralizer supplying device 12 is for supplying a neutralizer that neutralizes sulfuric acid, and a weak acid salt or a weak base can be used as the neutralizer. As the weak acid salt, for example, a carboxylic acid salt, a sulfonic acid salt, a phosphoric acid salt or the like can be used, and as the weak base, an amine or the like can be used. In the internal combustion engine of FIG. 1, the neutralizing agent is supplied in the form of droplets of an aqueous solution of a weak acid salt or a weak base.

When the neutralizing agent should be injected into the intake duct 4, the neutralizing agent pump 15 is driven so that the neutralizing agent discharged from the neutralizing agent pump 15 enters the intake duct 4 from the neutralizing agent injection nozzle 14. Is jetted. On the other hand, when the injection of the neutralizing agent into the intake duct 4 should be stopped, the neutralizing agent pump 15 is stopped. The neutralizer pump 15 is the electronic control unit 2.
It is controlled based on the output signal from 0.

Referring again to FIG. 1, an electronic control unit (ECU) 20 is composed of a digital computer, and a ROM (read only memory) 22 and a RAM (random access memory) which are connected to each other via a bidirectional bus 21. 23, a CPU (microprocessor) 24, an input port 25, and an output port 26. A pressure sensor 27 that generates an output voltage proportional to the pressure in the surge tank 3 is attached to the surge tank 3, and the output voltage of the pressure sensor 27 is input to the input port 25 via the AD converter 28. The CPU 24 calculates the intake air amount based on the output signal from the AD converter 28. Further, a water temperature sensor 29 that generates an output voltage proportional to the engine cooling water temperature is attached to the engine body 1, and the output voltage of the water temperature sensor 29 is input to the input port 25 via the AD converter 30.

Further, the throttle valve 6 has a throttle valve 6
The idle switch 31 is turned on when is at the idling opening and turned off when the accelerator pedal is depressed, and the output signal of the idle switch 31 is input to the input port 25 via the AD converter 32. further,
A crank angle sensor 33 that generates an output pulse each time the crankshaft of the engine body 1 rotates, for example, 30 degrees is connected to the input port 25. The CPU 24 calculates the engine speed based on the output pulse. On the other hand, the output port 26 is connected to the EG via the corresponding drive circuit 34.
It is connected to the R gas control valve 11 and the neutralizer pump 15, respectively.

In the internal combustion engine of FIG. 1, the EGR gas control valve 11 is opened to perform the EGR gas supply action unless the following cases occur. That is, the EGR gas control valve 11 is maintained in the closed state immediately after the engine is started, during engine no-load operation, or during engine high speed operation.
When the EGR gas supply action is performed, the EGR gas amount supplied to the engine is set to an optimum amount determined according to the engine operating state, that is, for example, the engine load (intake air amount / engine speed) and the engine speed. The opening degree of the gas control valve 11 is controlled. When the EGR gas supply action is performed in this way, the maximum combustion temperature in the combustion chamber can be lowered, and therefore the amount of nitrogen oxides discharged into the exhaust manifold 7 can be reduced.

By the way, when the EGR gas is supplied to reduce the emission of nitrogen oxides when the engine is cold, the inner surface of the cylinder bore, the piston ring, or the piston is caused by the sulfuric acid generated in the combustion chamber. It will be significantly worn. Therefore, the internal combustion engine of FIG. 1 is provided with the neutralizing agent supply device 12 so that the neutralizing agent is supplied from the neutralizing agent supply device 12 into the intake duct 4 when the EGR gas supply action should be performed when the engine is cold. There is. As a result, the sulfuric acid produced in the combustion chamber is neutralized by this neutralizing agent, so that it is possible to prevent the cylinder bore inner wall surface, the piston ring, or the piston from being significantly worn. That is, it is possible to secure the durability of the engine while reducing the amount of nitrogen oxide emissions when the engine is cold.

Further, in the internal combustion engine of FIG. 1, the neutralizing agent is supplied into the intake duct 4 in the form of droplets of an aqueous solution. Therefore, the sulfuric acid in the EGR gas supplied into the intake duct 4 is supplied. Are neutralized in this droplet before reaching the combustion chamber. Therefore, the durability of the engine can be surely enhanced. Further, when the neutralizing agent is supplied in the form of droplets of the aqueous solution in this manner, the droplets of the aqueous solution are supplied into the combustion chamber, and the heat of vaporization of water is relatively large, so the amount of nitrogen oxide emissions is It is possible to reduce the ratio of the EGR gas supplied into the combustion chamber while keeping it small. Therefore, the ratio of the air supplied into the combustion chamber can be increased, and unburned HC or particulates discharged into the exhaust manifold 7 can be reduced.

In this embodiment, the engine cooling water temperature THW
Is lower than a predetermined set temperature T1, for example, 40 ° C., it is determined that the engine is cold. However, whether or not the engine is cold can be determined based on, for example, the wall temperature of the intake passage, the temperature of the combustion chamber, the temperature of the engine body itself, the exhaust temperature, the engine oil temperature, or the like.

Next, referring to FIG. 2, a routine for executing the above-mentioned neutralizing agent supplying operation will be described. The routine shown in FIG. 2 is executed by interruption every predetermined set time. Referring to FIG. 2, first in step 41, E
It is determined whether or not the GR gas supply action is being performed.
When the EGR gas supply action is being performed, then the routine proceeds to step 42. In step 42, the engine cooling water temperature THW
Is lower than a preset set temperature T1, that is, whether the engine is cold. THW <T
If 1, that is, if the engine is cold, then step 43
Then, the neutralizer is supplied from the neutralizer supply device 12 into the intake duct 4. On the other hand, when the EGR gas supply operation is not performed in step 41, or in step 42
When THW ≧ T1, the process proceeds to step 44, and the supply action of the neutralizing agent is stopped.

Even when the engine is cold, combustion becomes considerably unstable when the engine cooling water temperature THW is extremely low, such as 25 ° C. or lower. In such a case EGR
The gas supply action may be stopped. The neutralizer supplying device 12 shown in FIG. 1 includes a neutralizer tank 13 for storing a dedicated neutralizer. However, since the engine cooling water contains a phosphate as a neutralizing agent, an amine, etc., the neutralizing agent injection nozzle 14 is connected to the engine cooling water passage so that the intake air is supplied when the EGR gas is supplied while the engine is cold. Duct 4
The engine cooling water may be supplied inside. Alternatively,
Since the window washer liquid contains a surfactant that acts as a neutralizing agent, the neutralizing agent injection nozzle 14 is connected to the window washer liquid tank, and when the EGR gas supply action is performed when the engine is cold, the inside of the intake duct 4 is It is also possible to supply the window washer liquid to. This eliminates the need to provide the neutralizer tank 13.

Further, in the neutralizing agent supply device 12 of FIG. 1, the neutralizing agent is injected into the intake duct 4. However, the neutralizing agent may be directly injected into the combustion chamber or may be injected into the EGR gas passage 10. Alternatively, the neutralizing agent may be injected into the exhaust manifold 7 upstream of the inlet of the EGR gas passage 10 or may be added in advance to the engine oil.

[0020]

As described above, the durability of the engine can be secured while the EGR gas is supplied while the engine is cold.

[Brief description of drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a flowchart for controlling the action of supplying a neutralizing agent.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine main body 4 ... Intake duct 7 ... Exhaust manifold 10 ... EGR gas passage 12 ... Neutralizer supply device 13 ... Neutralizer tank 14 ... Neutralizer injection nozzle 15 ... Neutralizer pump 29 ... Water temperature sensor

Claims (1)

[Claims] 1. An exhaust gas recirculation apparatus for an internal combustion engine, comprising an EGR gas passage connecting an engine exhaust passage and an engine intake passage to each other, when an EGR gas supply operation is performed when the engine is cold. , Combustion chamber, or EGR
An exhaust gas recirculation device equipped with a neutralizing agent supply means for supplying a neutralizing agent for neutralizing sulfuric acid into the gas passage.