Problem detection apparatus and method in exhaust purifying apparatus

This is a Continuation application of PCT Application No. PCT/JP2007/074106, filed Dec. 14, 2007, which was published under PCT Article 21 (2) in Japanese.

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-350134, filed Dec. 26, 2006, the entire contents of which are incorporated herein by reference.

1. Field of the Invention

The present invention relates to a problem detection apparatus and method in an exhaust purifying apparatus, in an exhaust filtering system such as a DPF.

2. Description of the Related Art

An exhaust filtering system such as a diesel particulate filter (DPF) system has a filter inside for collecting particulates included in exhaust gas of an engine, and purifies the exhaust gas through the filter. A filter is clogged with collected particulates. Therefore, appropriate amount of the collected particulates is automatically burnt, or cleaning or replacement is urged. An increased exhaust resistance in a DPF unit may increase a backpressure and exert an influence upon control of an engine.

Therefore, a DPF unit has a differential pressure sensor for measuring a pressure difference between the upstream side and downstream side of a filter, and judges whether a filter is clogged with particulates, based on the measurement value of such a differential pressure sensor. When a filter is clogged, a DPF unit issues a signal to urge an operator to manually burn the clogged particulates, or sends such a signal to a control unit for controlling an engine.

A filter in such a DPF unit is important, and exerts a large influence upon traveling of vehicles and environment, and is subject to large temperature changes and pressure fluctuations during operation. A filter is usually made of ceramic having a number of fine perforations on the surface, and may cause a leak of exhaust gas through a crack caused by an overload or a molten defect.

If particulates are deposited on a filter, the measurement value of a differential pressure sensor is increased by the deposited particulates. However, if a filter has a crack or a molten defect, the differential pressure increase caused by the deposited particulates is cancelled, and the differential pressure sensor can indicate a normal value in spite of deposition of particulates.

For, example, Jpn. Pat. Appln. KOKAI Publication No. 2003-155920 discloses the invention of a problem detection apparatus for a particulate filter. In the disclosed apparatus, a pressure difference before and after a particulate filter is measured by a differential pressure sensor, the measured differential pressure value is compensated by deposition of ash, and a particulate filter is checked for a clogging and a molten defect.

There are following problems in a conventional problem detection apparatus for a particulate filter.

In a problem detection apparatus for a particulate filter, a diagnosis is started only when an engine is judged steady. A threshold value used for the judgment is determined by an average engine speed and a time required to inject fuel, and is not determined unless the steady state of an engine is continued for a predetermined time. Thus, a diagnosis is not executed.

Further, a threshold value used for the judgment is determined irrespective of deposition of particulates. Therefore, a threshold value needs to be determined in expectation of an increase in backpressure by deposition of particulates. However, an ash calculation deposition value used for correcting a differential pressure is calculated simply proportional to a vehicle traveling distance. Therefore, even if the ash deposition amount becomes different depending on a driving history, the difference in the ash deposition amount is not reflected on the decision of a threshold value used for the judgment.

The present invention has been made in order to solve the above problems, and to provide a problem detection apparatus in an exhaust filtering system, which is configured to exactly detect a problem in a filter.

The problem detection apparatus in an exhaust filtering system of the present invention is configured as follow.

1. A problem detection apparatus in an exhaust purifying apparatus having a filter which is provided in an exhaust path in an internal combustion engine, and collects particulates in exhaust gas, and a differential pressure sensor which detects a pressure difference generated between the upstream side and downstream side of the filter, the problem detection apparatus comprising a differential pressure calculation means which calculates a value of a pressure difference between the upstream and downstream sides of the filter based on an operating state of the internal combustion engine; and a judgment means which calculates a difference P between an actual measurement value of the pressure difference between the upstream side and downstream side of the filter detected by the differential pressure sensor and a calculation differential pressure value from the differential pressure value calculation means, compares the difference P with a threshold value, and detects that the filter has a problem.

2. The problem detection apparatus in the exhaust purifying apparatus according to claim 1, wherein the judgment means has a first threshold value used for judging a clogging of the filter, and a second threshold value used for judging a leak of the filter, and judges that the filter has a problem, when a value of the difference P exceeds the first threshold value, or when a value of the difference P exceeds the second threshold value.

3. The problem detection apparatus in the exhaust purifying apparatus according to claim 2, wherein the first threshold value is calculated from an exhaust flow rate, and a clogging coefficient based on a soot calculation deposition value and ash calculation deposition value of the filter; and the second threshold value is calculated from an exhaust flow rate, and a leak coefficient based on a soot calculation deposition value and ash calculation deposition value of the filter.