System for estimating the soot load of a particle filter

Abstract

This system for evaluating the soot load of a particle filter integrated in a diesel engine exhaust system of a motor vehicle comprises: storage means for storing a pre-established map of unit soot emission rates for each speed/load operating point of the engine; acquisition means for acquiring the current operating point of the engine in order to determine the corresponding unit soot emission rate; and accumulator means for accumulating the unit emission rates while the engine is in operation in order to determine the soot load of the particle filter.

Description

The present invention relates to a system for estimating the soot load of a particle filter.

More particularly, the invention relates to such a system for evaluating the load in a particle filter integrated in the exhaust system of a motor vehicle diesel engine.

BACKGROUND OF THE INVENTION

It is known that engines of that type emit particles in operation, which particles are trapped in a filter. The filter thus becomes progressively clogged up, thereby increasing the back pressure in the exhaust system, and as a result it is necessary to regenerate the filter periodically.

To do this, a mode of engine operation is triggered for regenerating the particle filter, in which use is made of multiple injections of fuel into the cylinders of the engine in the form of pre-injection or pilot injection, main injection, and post-injection.

These various injections serve to increase the temperature of the exhaust gas, in particular by leading to post combustion during the expansion stage of the engine cycle and to catalytic post combustion of the unburnt hydrocarbons on an oxidation catalyst placed upstream from the particle filter, for example.

However, beyond a certain quantity of soot trapped in the filter, there is a risk of the filter breaking because of the thermomechanical stresses generated by burning the soot.

In order to avoid breaking the filter in this way, i.e. in order to limit thermomechanical stresses, a soot mass limit 6 maximum quantity of soot per liter of fuel is defined that must not be exceeded, with this maximum quantity being referred to as the soot mass limit (SML).

In order to comply with this SML criterion, it is therefore necessary to estimate the quantity of soot stored in the particle filter in order to regenerate it at the appropriate moment.

Several techniques already exist in the prior art for estimating the load of soot in a particle filter.

Thus, for example, one technique consists in using the back pressure across the inlet and outlet of the particle filter, thereby giving an image of the filter load.

The problem is that for given back pressure, it is possible to have various different soot loads depending on the type of driving that has been performed.

Another technique consists in recognizing the type of driving, and distinguishing various types of driving, e.g. five types, each associated with a corresponding soot emission rate. The problem with that technique is that it is lengthy to develop and requires a large amount of driving and testing on a roller bench.

OBJECT AND SUMMARY OF THE INVENTION

The object of the invention is thus to solve those problems.

To this end, the invention provides a system for evaluating the soot load of a particle filter integrated in a diesel engine exhaust line of a motor vehicle, the system comprising:

storage means for storing a pre-established map of unit soot emission rates for each speed/load operating point of the engine;

acquisition means for acquiring the current operating point of the engine in order to determine the corresponding unit soot emission rate;

corrector means for correcting the unit rate as determined in this way; and

accumulator means for accumulating the unit emission rates while the engine is in operation in order to determine the soot load of the particle filter.

According to other characteristics:

the corrector means comprise means for making a correction as a function of atmospheric pressure;

the corrector means comprise means for making a correction as a function of the temperature of air in the environment of the vehicle; and

the corrector means comprise means for making a correction as a function of the temperature of the vehicle engine cooling liquid.

BRIEF DESCRIPTION OF THE DRAWING

The invention can be better understood on reading the following description given purely by way of example and made with reference to the accompanying drawing, which is a block diagram showing the structure and the operation of an estimator system of the invention.

MORE DETAILED DESCRIPTION

The FIGURE shows a system for estimating the soot load of a particle filter integrated in an exhaust system of a motor vehicle diesel engine.

The system comprises means for storing a pre-established map of levels of soot emission corresponding to each speed/load operating point of the engine.

These storage means are given overall reference 1 in the FIGURE and, on the basis of means for acquiring the current operating point of the engine, in terms of speed and load, they make it possible to determine the corresponding unit rate of soot emission.

Accumulator means for accumulating these unit rates while the engine is in operation are then used to determine the soot load of the particle filter.

These accumulator means are given overall reference 2 and comprise means for adding a determined unit value to a previously accumulated quantity, e.g. stored in storage means 3.

Thus, the means for storing the map serve to store unit particle emission rates over the entire operating range of the engine for the various stabilized operating points of the engine.

On an engine test bench, it is entirely possible, for each speed and load operating point, to determine the rate of soot emission, e.g. in grams per second (g/s).

Such a map is of considerable interest insofar as it enables the time required to develop the system to be reduced considerably.

It suffices to place one engine (or two engines in order to make allowance for dispersion between engines) on an engine test bench together with particle analysis means in order to calibrate the map. Once the map has been calibrated, it can be used for all applications using the engine.

In addition, it is also possible to make use of means for correcting the determined unit emission rates.

Thus, for example, such correction means may include means for making a correction as a function of atmospheric pressure, and given overall reference 4 in the FIGURE, means for making a correction as a function of air temperature around the vehicle, given overall reference 5, and means for making a correction as a function of the temperature of the cooling liquid for the vehicle engine, as represented by general reference 6.

These various corrections are then applied at the output from the means for determining the unit emission rates via a corrector given overall reference 7.

Naturally, other dispositions could also be envisaged.

It will readily be understood that such a system presents certain advantages, in particular in terms of its simplicity of implementation.

Claims

1. A system for evaluating the soot load of a particle filter integrated in a diesel engine exhaust line of a motor vehicle, the system comprising:

storage means for storing a pre-established map of unit soot emission rates for each speed/load operating point of the engine;

acquisition means for acquiring the current operating point of the engine in order to determine the corresponding unit soot emission rate;

corrector means for correcting the unit rate as determined in this way; and

accumulator means for accumulating the unit emission rates while the engine is in operation in order to determine the soot load of the particle filter.

2. A system according to claim 1, wherein the corrector means comprise means for making a correction as a function of atmospheric pressure.

3. A system according to claim 1, wherein the corrector means comprise means for making a correction as a function of the temperature of air in the environment of the vehicle.

4. A system according to claim 1, wherein the corrector means comprise means for making a correction as a function of the temperature of the vehicle engine cooling liquid.