Internal combustion engine exhaust gas control apparatus and control method thereof

Abstract

An exhaust gas control apparatus includes a PM trapping filter provided in an exhaust gas passage of an internal combustion engine, an oxygen concentration sensor provided upstream of the filter, a device that estimates the air-fuel ratio of exhaust gas supplied to the oxygen concentration sensor, and a device that estimates the amount of PM trapped in the filter based on the estimated exhaust gas air-fuel ratio and the oxygen concentration sensor output. The amount of PM trapped in the filter is estimated using the fact that the oxygen concentration sensor output value changes according to the exhaust gas air-fuel ratio and the amount of PM accumulated on the oxygen concentration sensor. As a result, the structure of the exhaust passage is able to be kept simple because only an oxygen concentration sensor is added upstream of the filter.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention relates to an internal combustion engine exhaust gas control apparatus and a control method thereof. More particularly, the invention relates to technology for purifying particulate matter in exhaust gas.[0003]2. Description of the Related Art[0004]It is desirable to purify harmful gas components in exhaust gas produced by internal combustion engines used in automobiles and the like. More specifically, there is a need to purify particulate matter (hereinafter also referred to as “PM”) such as soot and soluble organic fraction (SOF) in exhaust gas produced by compression ignition internal combustion engines, i.e., diesel engines. One technology for purifying such particulate matter includes providing a filter in an exhaust passage of an engine and trapping the PM in the exhaust gas with this filter. This filter is typically referred to as a particulate filter, of more specifically in the case of a diesel en...

AI Technical Summary

Benefits of technology

[0008]This invention thus provides an internal combustion engine exhaust gas control apparatus, as well as a control method thereof, which is able to estimate the amount of PM trapped in a filter, and thus determine the timing at which to perform filter recovery, without complicating the structure of the exhaust passage.

[0010]The inventors discovered through intense study that the output value of the oxygen concentration sensor changes according to the air-fuel ratio of the exhaust gas supplied to the oxygen concentration sensor and the amount of particulate matter accumulated on the oxygen concentration sensor. For example, when the air-fuel ratio of the exhaust gas supplied to the oxygen concentration sensor is constant, the output value of the oxygen concentration sensor gradually decreases as the amount of particulate matter accumulated on the oxygen concentration sensor increases. Meanwhile, there is a corresponding relationship between the amount of particulate matter accumulated on the oxygen concentration sensor and the amount of particulate matter trapped in the filter. Ultimately, the output of the oxygen concentration sensor decreases as the amount of particulate matter trapped in the filter increases. Therefore, the amount of particulate matter trapped in the filter can be estimated by monitoring the oxygen concentration sensor output under the same exhaust gas air-fuel ratio conditions. All this requires is that an upstream oxygen concentration sensor be arranged in the exhaust passage upstream of the filter, so there is no need to provide a separate exhaust passage. As a result, it is possible to keep the structure of the exhaust passage simple and not limit the degree of freedom in its design.

[0021]As a result, the particulate matter accumulated on the filter can be burned off so the filter can be returned to its initial state in which no particulate matter is accumulated on it.

[0025]The output value of the oxygen concentration sensor changes not only according to a change in the exhaust gas pressure, but also according to a change in the exhaust gas air-fuel ratio. According to this structure, correcting the last value eliminates the effect from a change in the exhaust gas air-fuel ratio, making it possible to detect only the change in the pressure. As a result, it is possible to appropriately detect an abnormality in the filter.

[0030]The aspects of the invention described above are extremely advantageous in that they enable the amount of particulate matter trapped in the filter to be estimated such that the filter recovering timing can be determined, without complicating the structure of the exhaust passage.

Problems solved by technology

This makes the structure of the exhaust passage complex and limits the degree of freedom in design.

Images