FR3082564A1 - Method and device for controlling an internal combustion engine - Google Patents

Abstract

TITLE: Method and device for controlling an internal combustion engine Method by which the exhaust gases of the internal combustion engine (1) generated by combustion are passed through the cycle times of the engine through a gas system exhaust equipped with a three-way catalyst (3) and a particulate filter (5) or a four-way catalyst. To regenerate the exhaust gas system, part of the cycle times of the engine are carried out without injecting fuel and part of the cycle times of the internal combustion engine by combustion with a lack of air. Figure 1

Description

Description

Title of the invention: Method and device for controlling an internal combustion engine

Technical Field [0001] The present invention relates to a method and a device for controlling an internal combustion engine according to which the engine exhaust gases, generated by combustion, are passed through over the times of the operating cycle of the engine. internal combustion engine through an exhaust gas system equipped with a three-way catalyst and a particulate filter or through a four-way catalyst.

Prior art [0002] According to document DE 10 2013 221 598 A1, there is already known a method and a device for controlling an internal combustion engine according to which the engine exhaust gases generated by the cycle times are passed of the internal combustion engine through a three-way catalyst and a particulate filter.

There is also known a process for regenerating the particulate filter according to which the soot particles retained in the particulate filter are burnt in order to empty the particulate filter again. To perform such a regeneration of the particulate filter, it is necessary to add to the exhaust gases a sufficient quantity of oxygen to allow the combustion of the soot particles.

DESCRIPTION AND ADVANTAGES OF THE INVENTION The invention relates to a method for controlling an internal combustion engine of the type defined above, characterized in that to regenerate the exhaust gas system, part of the cycle times of the internal combustion engine is performed without injecting fuel and part of the cycle times of the internal combustion engine with combustion with an air fault.

The invention also relates to a device for applying the method of controlling an internal combustion engine as defined above, characterized in that it comprises means for regenerating the particle filter which perform part of the cycle times of the internal combustion engine without injecting fuel and part of the cycle times of the internal combustion engine with combustion performed in lack of air.

In other words the method and the device according to the invention for controlling an internal combustion engine have the advantage of having an oxygen supply, sufficient for regeneration and at the same time reducing the minimum harmful products expelled with exhaust gases, during the regeneration phase. In particular, excessive emission of nitrogen oxides (NOx) is avoided. This allows a particulate filter or a four-way catalyst to be regenerated, without exceeding the limit value imposed on the exhaust gases of the internal combustion engine.

The choice of cycle times without injecting fuel compared to cycle times with lack of air makes it possible to control the amount of oxygen introduced into the exhaust gas system. This allows controlled combustion of the soot particles loaded into the exhaust system. In a particularly simple manner, the cycle times without fuel injection can be associated with one or more determined cylinders of the internal combustion engine. As a variant, provision can also be made to distribute the cycle times without fuel injection between the cylinders according to a predefined pattern. In particular, it is thus possible to introduce any predefined quantity of oxygen into the exhaust gas system. Cycle times with lack of air must be performed with a lambda coefficient of less than 0.8. This allows the emission of nitrogen oxides NOx to be kept to a minimum. Such regenerative operation must also depend on the temperature prevailing in the exhaust gas system. The temperature of the exhaust gas system being regenerated can be monitored to detect an excessive exothermic reaction in the exhaust gas system in time. This allows for appropriate measures to be taken to avoid particularly significant overheating of the exhaust gas system during regeneration and therefore to avoid damage to the exhaust gas system.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described below in detail with the aid of exemplary embodiments represented in the appended drawings in which:

[Fig. 1] diagrammatically shows an internal combustion engine whose exhaust gases pass through a three-way catalyst and a particle filter, [0011] [fig.2] shows the relationship between the gross emissions of harmful products by a combustion engine internal according to FIG. 1 as a function of the lambda coefficient, and [0012] [fig.3] shows the content of harmful substances, downstream of the three-way catalyst, as a function of the lambda coefficient.

DESCRIPTION OF AN EMBODIMENT [0014] FIG. 1 schematically shows an internal combustion engine 1 in which combustion takes place in the cycle times of the internal combustion engine 1. This is for example of a gasoline internal combustion engine which is for example a four-stroke internal combustion engine, an intake time, a compression time, an explosion time and an exhaust time. One of these four cycle times of the internal combustion engine will be called active time because in this cycle time the air and fuel mixture introduced into the combustion chamber of the engine is ignited.

This combustion generates exhaust gases from the internal combustion engine 1 which are first directed through a three-way catalyst 3 by an exhaust pipe 2. Downstream of the catalyst 3, the gases exhausts pass through another exhaust pipe 4 to pass through a particle filter 5. Downstream of the particle filter 5, the exhaust gases from the engine 1 arrive via an exhaust gas pipe 6 to the environment. Thanks to this exhaust gas system equipped with the catalyst 3 and the particle filter 5, the exhaust gases emitted to the atmosphere are very largely cleaned of pollutants.

Alternatively, an exhaust gas system equipped with a four-way catalyst is used. It is a component uniting in a single element, the three-way catalyst and the particulate filter. This works like that of a three-way catalyst and a particulate filter. Although the following description of the invention is given in the case of an exhaust gas system equipped with a separate particle filter 5 and a catalyst 3, this description also applies, correspondingly, to an exhaust gas system equipped with a four-way catalyst.

Catalyst 3 makes it possible to reduce three main components of the exhaust gases. Catalyst 3 removes the harmful combustion products HC (hydrocarbons), CO (carbon monoxide) and NOx (Nitrogen oxides) from exhaust gases. As for this catalyst 3 performs three different chemical reactions, this catalyst is also called three-way catalyst. For the catalyst 3 to be able to perform this function, the ratio of oxygen to fuel during combustion must be set to a stoichiometric value, that is to say, the quantity of oxygen necessary for fuel combustion. This ratio between oxygen and fuel is also expressed by the lambda coefficient; a lambda coefficient equal to 1 represents the stoichiometric ratio of air to fuel; a lambda coefficient lower than 1 corresponds to an excess of fuel, that is to say a lack of oxygen; a lambda coefficient greater than 1 corresponds to an excess of oxygen. The lambda coefficient must be kept around the value 1 with close tolerances and must not deviate from it by more or less than half a percent (+ - 0.005).

The catalyst 3 is followed by the particle filter 5 used to remove the soot particles from the exhaust gas of the internal combustion engine 1. Such soot particles are removed from the exhaust gases by passing the gases d exhaust through a porous wall structure of the particulate filter 5. The porous structure of the wall of the particulate filter 5 separates the soot particles (smoke black) from the exhaust gases due to their physical size. Thus over time, significant amounts of soot accumulate in the particulate filter 5 which deteriorates the filtering effect or the flow of exhaust gases through the particulate filter 5.

For this, it is necessary to remove from time to time, the soot particles deposited in the particle filter 5 of the exhaust gas system; for this, the internal combustion engine 1 is controlled in an operating state in which, on the one hand, the particle filter 5 is at a sufficiently high temperature and, on the other hand, the exhaust gases introduced into the gas system d exhaust still contain oxygen. Thanks to the high temperature prevailing in the particulate filter 5 and the supply of oxygen available in the exhaust gases, the soot or black smoke particles deposited in the particulate filter will be burned. This process again restores the original behavior of the particle filter 5 and is therefore also called the regeneration process. During regeneration, the catalyst 3 can no longer operate in its optimal operating range to eliminate the various harmful compounds contained in the exhaust gases. During regeneration, the exhaust gas pipe 6 will emit a higher quantity of pollutants. The invention makes it possible, according to its method and its device, to reduce or completely avoid the emission of polluting material during regeneration of the particulate filter 5.

To understand the invention, a precise understanding of the operation of the catalyst is required. For this, FIG. 2 shows the gross emissions of combustion, that is to say the composition of the exhaust gases passing through the catalyst. 3 through the exhaust gas line 2. In FIG. 3, the exhaust gases are led downstream of the catalyst 3, that is to say the exhaust gases which have passed through the catalyst 3 via the line exhaust gas 4 on the particulate filter 5. In addition Figures 2 and 3 show the composition of pollutants which vary due to the change in the lambda coefficient.

Figure 2 shows the gross emissions of the internal combustion engine 1. For NOx oxides, for a lambda value less than 0.8, there will first of all be only a small generation of NOx oxides which nevertheless increases by significantly with the value of the lambda coefficient; for a lambda coefficient of around 1.1 we reach the maximum. If the oxygen content continues to increase, the content of nitrogen oxides NOx decreases again. For the behavior of CO we note that in the event of lack of oxygen, there will be a lot of CO gas; the CO content decreases with the increase in the lambda coefficient and for a coefficient equal to or greater than 1, very little CO is generated. For HC hydrocarbons, we note that approximately for a lambda coefficient equal to 1, we generate few HC hydrocarbons and for a significant difference both in the positive and in the negative direction, the HC hydrocarbon content increases significantly. FIG. 2 also shows the operating window 21 for a lambda coefficient equal to 1 + / to half a percent.

Figure 3 shows the effect of catalyst 3 on exhaust gases as a function of the lambda coefficient. As it seems clear, around the lambda 1 value, we are at the very least polluting matter. For a lower oxygen content, i.e. a lambda coefficient equal to 0.975, the exhaust gases still contain significant fractions of CO, HC and NOx. But if the combustion engine is operated to release an excess of oxygen, the pollutants CO and HC will be greatly reduced as has already been seen above. The content of harmful nitrogen oxides increases significantly.

If the internal combustion engine 1 is operated so that the exhaust gases contain an excess of air, necessary for the regeneration of the particle filter 5, this will result in particular in higher missions of nitrogen oxides NOx. In particular during regeneration, nitrogen oxide emissions can significantly deteriorate the exhaust gases, in particular exceeding the authorized limit values.

The invention proposes not to carry out each combustion identically but to perform part of the combustion with a lack of air and part of the cycle times with normal combustion without injection, that is to say say without combustion. If there is no combustion in the active time, the exhaust gases will not contain any harmful matter but only the ambient air pumped by engine 1 in the exhaust gas system. Since there is no combustion, the ambient air naturally contains a very high fraction of oxygen. For the combustion phases in the other active times, the combustions are carried out by generating only a small amount of NOx oxides. For this we reduce the lack of air in the active times during which there is a combustion, until these combustions are done with a lambda coefficient less than 0.8 and better still less than 0.75. For such a lambda coefficient, we will have as it appears in Figure 2, only a very small amount of NOx oxides and that is why there is no disadvantage that the catalyst 3 is not able to reduce significantly a possible emission of NOx oxides. The mixture of exhaust gases from active times with air fault and active times without fuel injection, that is to say without combustion, results overall for the exhaust gases by an excess of air that is, catalyst 3 will operate in a range where the amount of CO and HC downstream of catalyst 3 is small. As the active times for which there is combustion with air defect, occur in a range in which only a small amount of NOx oxides is created, this exhaust gas contains only a very small amount of NOx oxides and the low possibility of catalyst 3 to reduce NOx oxides in this range of the lambda coefficient does not matter. Such an operation thus makes it possible to generate, as previously, an exhaust gas having a high oxygen content and for which at the same time the content of C3 harmful products HC, CO and NOx is low.

To introduce a defined quantity of air into the particle filter 5, the active times without fuel injection can be influenced compared to the active times with combustion and lack of air. The fuel, we will introduce a larger, corresponding part of air in the particulate filter. This is particularly simple if the internal combustion engine 1 has several cylinders in which there are active times. For example in the case of a six-cylinder engine, it is possible to choose to operate only one cylinder or also two cylinders without injecting fuel to introduce the desired quantity of air into the particle filter 5. Alternatively it is also possible to achieve such a ratio between the active times without fuel injection compared to the active times with combustion and lack of air in that selectively, the fuel injection is cut in certain cylinders. For example, in the case of an internal combustion engine with four cylinders, one can have every fifth stroke active without injecting fuel. For this it is always necessary to choose another cylinder for this active time without injection.

As it appears in Figure 2 the release of NOx oxides is particularly low if the combustion is done with a lambda coefficient significantly less than 0.8 that is to say a lack of air of more than 20 % relative to the stoichiometric value. Preferably, provision may in particular be made for an operating range with a lambda coefficient of less than 0.75.

Such operation of the internal combustion engine to introduce oxygen into the particulate filter for its regeneration is naturally only advantageous if the temperature of the particulate filter is above a threshold. Typically, regeneration in the particulate filter can only take place if the temperature in the particulate filter 5 exceeds 600 ° C. In addition, it may also be useful to monitor the temperature of the particulate filter. This is particularly useful if the soot particle load of the particulate filter 5 is not known and since the degree of temperature increase in the particulate filter 5 is not predictable. For such an operating state, it may be necessary to use the temperature of the particulate filter 5 and, if necessary, to stop the operation which introduces oxygen into the particulate filter 5. In no case will the particulate filter must be overheated by the combustion of soot because the temperatures which occur can mechanically damage the particulate filter 5.

NOMENCLATURE OF MAIN COMPONENTS [1] 1 Internal combustion engine [2] 30 2 Exhaust gas line [3] 3 Catalyst [4] 4 Exhaust line [5] 5 5 Particulate filter [2] 6 Exhaust pipe [21] 21 Operation window

Claims (1)

claims [Claim 1] Method of controlling an internal combustion engine (1) in which the exhaust gases of the engine generated by combustion are passed through the operating cycles of the internal combustion engine through an exhaust gas system equipped with a three-way catalyst (3) and a particulate filter (5) or a four-way catalyst, process characterized in that to regenerate the exhaust gas system, part of the cycle times of the internal combustion engine is carried out without injecting fuel and part of the cycle times of the internal combustion engine by combustion with a lack of air. [Claim 2] Method according to claim 1, characterized in that the cycle times without fuel injection are chosen in relation to the combustion cycle times with a lack of air so as to introduce a predefined quantity of oxygen into the gas system exhaust. [Claim 3] Method according to claim 2, characterized in that the cycle times without fuel injection are associated with specific cylinders of the internal combustion engine (1). [Claim 4] Method according to claim 2, characterized in that the cycle times without fuel injection are distributed according to a predefined pattern between the cylinders of the internal combustion engine (1). [Claim 5] Method according to one of the preceding claims, characterized in that cycle times are performed by combustion with a lack of air for a lambda coefficient of less than 0.8. [Claim 6] Method according to one of the preceding claims, characterized in that regeneration is performed only if the temperature of the exhaust gas system is above a threshold. [Claim 7] Method according to one of the preceding claims, characterized in that during regeneration the temperature of the gas system is monitored [Claim 8] exhaust and regeneration is ended if the temperature of the particulate filter exceeds a safety threshold. Control device of an internal combustion engine (1) according to which the exhaust gases of the internal combustion engine (1), generated by the combustion in the cycle times of the internal combustion engine, are passed through a system exhaust gas equipped with a three-way catalyst (3) and a particulate filter (5) or a four-way catalyst, device characterized in that it comprises means for regenerating the filter particles (5) performing part of the cycle times of the internal combustion engine (1) without fuel injection and part of the cycle times of the internal combustion engine (1) with combustion under a lack of air.