Method of diagnosing the presence of an exhaust after-treatment component and a use of the method for vehicle on-board diagnosis

Description

BACKGROUND AND SUMMARY

The present invention relates to a method for diagnosing the presence of an internal combustion engine exhaust aftertreatment component on a vehicle.

In recent years, statutory requirements pertaining to emissions from Diesel engines have been tightened up. For example, new legislation regarding on-board diagnosis requires that the presence of a so-called pre-catalyst is determined.

It is desirable to provide a method to determine whether an aftertreatment component in an aftertreatment system is present or not.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail below with reference to embodiments shown in the accompanying drawings.

In FIG. 1, an internal combustion engine with an exhaust aftertreatment system for utilizing the invention is illustrated diagrammatically.

FIG. 2 is a first graph illustrating temperature variations in the exhaust aftertreatment system shown in FIG. 1.

FIG. 3 is a second graph illustrating temperature variations in the exhaust aftertreatment system.

DETAILED DESCRIPTION

FIG. 1 shows a general configuration of an exhaust aftertreatment system for an internal combustion engine 10, including a first exhaust pipe segment 11 leading exhausts from the engine to a pre-catalyst 12. The pre-catalyst is connected to a selective catalyst reactor 13 via a second exhaust pipe segment 14. A third exhaust pipe segment 15 leads exhausts from the reactor 13 to the atmosphere.

A temperature sensor 16 is positioned at the second exhaust pipe segment 14 for measuring the temperature of the exhaust stream exiting the pre-catalyst 12. The temperature is measured continuously over a time period to provide a first temperature signal with fluctuating amplitude that is recorded by a data processor 17. A typical temperature/time graph is shown in FIG. 2. Due to the fact that the pre-catalyst 12 comprises a thermic mass, i.e. the reactor monolith, the exhaust temperature variations are filtered when the exhaust stream passes through the pre-catalyst.

An example of a typical un-filtered temperature graph is shown in FIG. 3, showing temperature variations with higher frequency than in FIG. 2. If the pre-catalyst 12 is not present in the exhaust aftertreatment system, the temperature sensor 16 will provide a signal with a similar signature as the graph shown in FIG. 3.

The recorded temperature signal is modified by the data processor 17 to provide a second modified temperature signal. The first and second temperature signals are compared to detect any significant difference between the signals. The modified signal may be obtained by any type of analysis of the temperature signal that is based on signal frequency or signal derivative. For example, a low-pass filter in the data processor 17 may be used for removing signals with frequency over a certain level. By integrating the unfiltered and filtered temperature signals and calculating the difference between the two, it is possible to determine whether the catalyst reactor monolith is present. A large difference is the result when the monolith is missing and a small difference when the monolith is present.

If the pre-catalyst is not present in the aftertreatment system, the first signal will have a signature similar to the graph of FIG. 3. When the signal has been modified by means of the data processor 17, the resulting second signal will have a signature similar to the graph of FIG. 2. Thus, the comparison between the two signals positively indicates that no catalyst reactor monolith is present upstream the temperature sensor 16.

If the pre-catalyst is present, both first and second signals will have signatures similar to the graph of FIG. 2. Thus, the comparison between the two signals positively indicates that a thermic mass, e.g. a catalyst reactor monolith is present in the aftertreatment system upstream the temperature sensor 16.

The invention is not to be regarded as being limited to the illustrative embodiments described above, but a number of variants and modifications are possible within the scope of the following patent claims. For example, the method according to the invention can be applied to any type of aftertreatment component, as long as it comprises a thermic mass. The aftertreatment component may for example be a particle filter. It is preferable that the aftertreatment component being diagnosed with the method according to the invention has a larger thermic mass than any other aftertreatment component positioned upstream. The comparison of the two temperature signals can be performed in many different ways, both analogical and digital.