Exhaust gas purification system for internal combustion engine

Abstract

There is provided a technology that enables easier adjustment of the temperature of an exhaust gas purification apparatus to a target value by supplying an appropriate quantity of fuel to the exhaust gas purification apparatus even in the case where sub-injection and exhaust addition are performed in an exhaust gas purification system for an internal combustion engine. The system includes a fuel addition valve that adds fuel to the exhaust gas in an exhaust passage upstream of the exhaust gas purification apparatus and unburned fuel discharge unit for discharging gas containing unburned fuel from the combustion chamber of the internal combustion engine to the exhaust passage, wherein when supplying fuel to the exhaust gas purification apparatus to make the temperature of the exhaust gas purification catalyst equal to a target temperature, the quantity of fuel supplied by the fuel addition valve is controlled by a feedback control, and the quantity of fuel supplied by the unburned fuel discharge unit is controlled by an open-loop control.

Description

TECHNICAL FIELD[0001]The present invention relates to an exhaust gas purification system for an internal combustion engine.BACKGROUND ART[0002]There is a known technology in which a particulate filter (which will be simply referred to as a “filter” hereinafter) is provided in an exhaust passage of an internal combustion engine so that particulate matter (which will be referred to as “PM” hereinafter) contained in the exhaust gas of the internal combustion engine will not be emitted to the atmosphere.[0003]PM contained in the exhaust gas is once trapped by the filter. As the amount of PM trapped in the filter becomes larger, the pressure of the exhaust gas upstream of the filter will increase, and there is a possibility that a decrease in the output power of the internal combustion engine and a deterioration in the fuel economy will be invited thereby. In such cases, the PM deposited on the filter can be removed by oxidizing it. Such removal of PM trapped on the filter will be referr...

AI Technical Summary

Benefits of technology

[0013]The present invention has been made in view of the above described problems, and an object of the present invention is to provide a technology that enables easier adjustment of the temperature of an exhaust gas purification apparatus to a target value by supplying an appropriate quantity of fuel to the exhaust gas purification apparatus even in the case where the sub-injection and the exhaust addition are performed in an exhaust gas purification system for an internal combustion engine.

[0022]On the other hand, the quantity of fuel supplied through the fuel addition valve can be adjusted more precisely as compared to the quantity of fuel supplied through the unburned fuel discharge means. Therefore, it is possible to correct the fuel supply quantity by feedback-controlling the quantity of fuel supplied through the fuel addition valve. Consequently, the temperature of the exhaust gas purification apparatus can be adjusted to the target value quickly.

[0023]According to the present invention, said exhaust gas purification apparatus is provided with a catalyst, and the supply of fuel by said unburned fuel discharge means may be stopped when the temperature of the catalyst is not lower than an active temperature.

[0028]If fuel is supplied only through the fuel addition valve, fuel may adhere to the upstream end portion of the exhaust gas purification apparatus, or the temperature of the upstream end portion may decrease, in some cases. This leads to the occurrence of clogging in the upstream end portion and / or a decrease in the overall temperature of the exhaust gas purification apparatus, in some cases. In contrast, if the supply of fuel by the unburned fuel discharge means is performed periodically, reactive fuel can be supplied to the exhaust gas purification apparatus, and therefore temperature of the upstream end portion can be raised. This can prevent clogging in the upstream end portion of the exhaust gas purification apparatus and a decrease in the overall temperature of the exhaust gas purification apparatus from occurring.

[0030]As described in the foregoing, according to the present invention, in an exhaust gas purification system for an internal combustion engine, easier adjustment of the temperature of an exhaust gas purification apparatus to a target value can be achieved by supplying an appropriate quantity of fuel to the exhaust gas purification apparatus even in the case where the sub-injection and the exhaust addition are performed.

Problems solved by technology

As the amount of PM trapped in the filter becomes larger, the pressure of the exhaust gas upstream of the filter will increase, and there is a possibility that a decrease in the output power of the internal combustion engine and a deterioration in the fuel economy will be invited thereby.

The sulfur components thus stored is more difficult to be released than NOx and accumulates in the NOx catalyst.

For this reason, it is sometimes more difficult to control the fuel quantity precisely in the sub-injection than in the exhaust addition.

Furthermore, when the sub-injection is performed, there is a possibility that lubricant oil may be diluted due to what is called bore flushing in which fuel adheres to the cylinder wall surface to wash away the lubricant oil.

Furthermore, if an EGR apparatus is provided, there is a possibility that fuel may enter the EGR apparatus to cause clogging of an EGR cooler or to make the EGR valve difficult to operate.

Furthermore, if the distance from the combustion chamber to the exhaust gas purification apparatus is long, it is difficult to control the sub-injection quantity when regulating the sub-injection quantity in order to adjust the temperature of the exhaust gas purification apparatus to a target value, because it takes time for the temperature of the exhaust gas purification apparatus to change.

Therefore, if only the exhaust addition is performed, there will sometimes occur HC poisoning in which HC adheres to the upstream end portion of the catalyst.

Furthermore, there is a possibility that fuel that reaches the catalyst in a liquid state may evaporate in the catalyst to decrease the temperature of the upstream portion of the catalyst.

For the above reasons, when the exhaust addition is performed, there is a possibility that clogging in the upstream end of the catalyst may occur, and / or the overall temperature of the catalyst may become lower than active temperatures, thereby making regeneration of the filter impossible.

It is difficult to adjust the temperature of the filter or the NOx catalyst to a target value only by the sub-injection, because it is difficult to control the quantity of fuel precisely.

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