Exhaust Purifier for Internal Combustion Engine

Abstract

An addition valve is provided upstream of an exhaust gas purifying catalyst (NOx catalyst) in an exhaust pipe and in the vicinity of a water jacket in a cylinder head, in addition to a fuel injection valve injecting fuel for combustion in a combustion chamber. The addition valve injects a reducing agent in an addition amount in accordance with an operation state of an engine. Using an engine coolant temperature correlated to a temperature of the addition valve, a target addition interval of the addition valve is made shorter with increase in the engine coolant temperature, so that the addition amount is increased (step 130). The temperature of the exhaust gas purifying catalyst (catalyst bed temperature) is raised as a result of increase in the addition amount. Here, a target injection amount of fuel, representing one of parameters other than the addition amount that affect the catalyst bed temperature, is restricted by using an injection amount upper limit, such that the catalyst bed temperature does not exceed an upper limit of an allowable range (steps 240, 250).

Description

TECHNICAL FIELD[0001]The present invention relates to an exhaust gas purifying apparatus of an internal combustion engine, configured to provide an addition valve upstream of an exhaust gas purifying catalyst in an exhaust pipe for injection of a reducing agent, in addition to a fuel injection valve injecting fuel burnt in a combustion chamber of the internal combustion engine.BACKGROUND ART[0002]In an internal combustion engine operating by burning an air-fuel mixture at a high air-fuel ratio (lean atmosphere) in a wide operation region, such as a diesel engine, generally, an NOx catalyst attaining a function to purify a nitrogen oxide NOx in the exhaust gas is provided in an exhaust pipe thereof. As the NOx catalyst, for example, a catalyst carrying both an NOx absorbent capable of absorbing nitrogen oxide NOx in the presence of oxygen and a precious metal catalyst (precious metal) capable of oxidizing hydrocarbon HC on a honeycomb structure (carrier) made of porous ceramics is ad...

AI Technical Summary

Benefits of technology

[0015]According to this configuration, as the addition valve is arranged in the vicinity of the coolant pipe provided in the internal combustion engine, the temperature of the addition valve tends to be affected by the heat of the coolant that flows in the coolant pipe. When the temperature of the coolant is not so high, such as during a low or intermediate load operation or the like of the internal combustion engine, the addition valve is cooled as a result of heat removal by the coolant, and clogging of the injection hole is unlikely. When the temperature of the coolant is high, such as during a high load operation or the like of the internal combustion engine, efficiency in cooling the addition valve is lowered, and the temperature of the addition valve may exceed the temperature at which the volatile component in the reducing agent evaporates. Therefore, according to the present invention, the effect of the invention described above is reliably obtained by employing the temperature of the coolant as the value corresponding to the temperature of the addition valve and by increasing the addition amount based on the corresponding value.

[0016]Further preferably, the control unit restricts an amount of fuel injection from the fuel injection valve, as control of the parameter.

[0017]In the internal combustion engine and the exhaust gas purifying apparatus, as the amount of fuel injection from the fuel injection valve is decreased, the temperature of the exhaust gas and the catalyst is accordingly lowered. The injection amount is thus restricted as in the present invention, so that the injection amount is decreased as compared with a case where the injection amount is not restricted, and the temperature of the exhaust gas is lowered. Then, the temperature of the catalyst is lowered, and it is less likely that the upper limit of the allowable range is exceeded. In this manner, according to the present invention, the effect of the invention described above is reliably obtained.

[0018]Further preferably, when at least one of the temperature of the addition valve and the corresponding value is high, the control unit restricts the amount of fuel injection to a larger extent than when at least one of the temperature of the addition valve and the corresponding value is low.

[0019]Here, as the injection amount is restricted to a larger extent, an amount of lowering in the temperature of the exhaust gas and the catalyst as a result of restriction becomes greater. In this regard, in the present invention, when at least one of the temperature of the addition valve and the value corresponding thereto is high (when the degree of increase in the addition amount is great and an amount of increase in the temperature of the catalyst is great), the injection amount is restricted to a larger extent than when at least one of the temperature of the addition valve and the value corresponding thereto is low. In this manner, the degree of restriction of the injection amount is varied in accordance with at least one of the temperature of the addition valve and the value corresponding thereto, so that undue lowering in the engine output due to excessive restriction of the injection amount can be suppressed when at least one of the temperature of the addition valve and the value corresponding thereto is relatively low. In addition, when at least one of the temperature of the addition valve and the value corresponding thereto is high, such a situation that restriction of the injection amount is insufficient (the injection amount is great) and the temperature of the catalyst consequently exceeds the upper limit of the allowable range can be suppressed.

[0020]Further preferably, the control unit decreases an amount of fuel injection from the fuel injection valve, as control of the parameter.

Problems solved by technology

On the other hand, the increased reducing agent burns, and the temperature of the exhaust gas purifying catalyst is raised by the heat generated during the combustion.

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