PROCEDURE FOR THE CLEANING OF EXHAUST GASES OF A COMBUSTION ENGINE

The present invention relates to processes for cleaning exhaust gas of internal combustion engines of motor vehicles, and more particularly to methods for regenerating a particulate filter system of an engine.

The system of filtering particles comprises a particle filter that captures soot particles emitted by the engine. To prevent clogging, carried out periodic phases of regeneration of the filter for burning the particulates trapped, by raising the exhaust gas temperature so as to reach a temperature at the particulate filter between 570 °c and 650 °c.

There are methods for regenerating the particulate filter. The document FR2831923 provides a fuel supply method based on various conditions of the engine to remove particles from the stored. The method controls an injection system in the cylinders (or combustion chambers) of the engine and an injection system in the exhaust line of the engine. For example, when the engine is operating under a low load, the fuel injection system into the combustion chambers is used to warm the exhaust gas of the engine, by performing a secondary injection.

A drawback of this method is that when the filtering system is disposed away from the injection system into the combustion chambers of the engine, as is the case for example when the filtering system is under the floor of the vehicle, it is not always possible to activate regeneration, because the threshold temperature of the catalyst to burn fuel from the secondary injection is not always attained.

The document W02004099578 provides a regeneration process in which the fuel injection system in the cylinders is provided for obtaining a certain oxygen concentration in the exhaust gas stream, without giving aIncrease in exothermic reaction that might damage the turbocharger turbine that is downstream.

An object of the invention is to overcome the disadvantages described above, by providing a method capable of activating a regeneration regardless of engine conditions and regardless of the distance to the filtering system.

The invention provides for this purpose a method for cleaning exhaust gas of an internal combustion engine which comprises a step of detecting the need for engaging a regeneration of a particulate filter system and a step of activating a regeneration. According to the invention, the activating step includes:

• a step of operating a fuel injection system in the engine cylinders to increase the exhaust gas temperature upstream of an additional catalyst, placed upstream of a fuel injection system in the exhaust system of the engine, according to a first mode of operation;
• a control step of the fuel injection system in the engine cylinders to increase the temperature of the additional catalyst, according to a second mode of operation, when the value of [...] 1 additional oxidation catalyst temperature is above a threshold of TADOC 1;
• a control step of the fuel injection system in the exhaust line when the value [...] 2 of the catalyst from the filtration system is greater than a threshold tadoc2.

The method according to the invention, and advantages thereof will be better understood upon reading of the detailed description of an embodiment example the least and limiting, and illustrated in the Figure 1.

With reference to Figure 1, the motor 2 of the present embodiment of the invention includes a cylinder head 4 containing cylinders 6 in which are mounted movable pistons 8 wherein emerge and fuel injectors 10.

The engine 2 comprises an intake circuit 12 emergingIn the cylinders 6 and an exhaust circuit 14 whose input is at the same rollers. The motor 2 comprises a circuit 16 of exhaust gas recirculation or EGR flow for removing a fraction of the exhaust gas at the outlet of the cylinders for the reinjection into the intake circuit. The EGR circuit comprises in particular a controllable valve 18. the EGR flow path is closed when performing a regeneration of the particulate filter.

The engine 2 includes a turbocharger comprising a turbine 20 22 set in motion by the exhaust gas flowing through the circuit 14 and connected to a compressor 24 producing compression of gas flowing through the inlet line 12.

The anti-pollution device of the engine exhaust includes components that are present in the exhaust line 14. These components include a filtration system having a particulate filter 30, 28 an oxidation catalyst disposed upstream of the particulate filter 30, a temperature sensor 40 which provides a value [...], placed between the particle filter 30 and the oxidation catalyst 28.

The particle filter 30 can be a catalytic particulate filter containing a layer of catalyst material.

The temperature sensor 40 measures the temperature of the exhaust gas flowing between the oxidation catalyst and the particulate filter 28 30; [...] 2 value is used to determine the outlet temperature of the oxidation catalyst 28 and also the inlet temperature of the particulate filter 30. It is considered that these two temperatures are equivalent.

The anti-pollution device also includes an electronic control unit 41, also called a calculator. This unit 41 is adapted to receive data from various sensors, such as temperature sensor 40 which provides the data [...], and is adapted to control the various devices of the motor and of the pollution control device.

The anti-pollution device 10 also includes a system for injecting fuel into the engine combustion chambers 8 2. system 10 injection, controlled by the unit 41, isCan inject fuel for generating torque and also to increase the exhaust gas temperature

The anti-pollution device also includes a fuel injection system 32 disposed in the exhaust system of the engine 2 in the oxidizing catalytic converter 28. The system 32 is used when the value of [...] 2 is greater than or equal to a threshold temperature, called [...], for activating the oxidation catalyst 28.

The device is characterized in that it also includes additional means for heating the exhaust gas upstream of the oxidation catalyst 28.

These additional means comprise an additional oxidation catalyst 26, a sensor 36 which provides a value tsdoc1. In accordance with the single fig., the additional oxidation catalyst 26 is placed upstream of the fuel injection system 32 disposed in the exhaust system of the engine 2 .le sensor 36 is placed between the catalyst 28 and the additional catalyst 26. In addition to the catalyst of the additional sensor 28 and 36, the system 10 for injecting fuel into the engine combustion chambers 8 2 is used for delivery of fuel in gaseous form to the additional catalyst 26 when the value of [...] 1 is greater than or equal to a threshold temperature, called [...], for activation of the additional oxidation catalyst 26.

The additional means can also include a system for reducing the inlet gas flow rate, so as to increase the richness. In this example non-limiting embodiment, the electronic control unit 41 may act on the throttle housing 60 which is located in the intake circuit 12, so as to restrict the inlet gas flow rate entering the cylinders 8 of the engine. This permits the richness, [...] to say the ratio between the fuel and the gas inlet, which is increased, thereby increasing the exhaust gas temperature.

The process for decontaminating, implemented by the emission control described above, comprises a step of detecting the need for engaging a regeneration of theSystem of filtering particles and a step of activating a regeneration. The step of sensing the need can be by any method known to the skilled person, such as the use of a differential pressure sensor (not shown) disposed across the filtration system, or through a mapping stored in the memory of the unit 41 to determine the particle loading of the filter 30 in accordance with the engine operating conditions.

According to the invention, the step of activating the regeneration comprises:

• a control step of the system 10 for injecting fuel into the cylinders of the engine 8 2 to increase the exhaust gas temperature upstream of the additional catalyst 26, placed upstream of a fuel injection system in the exhaust system of the engine, according to a first mode of operation;
• a control step of the injection system 10 8 of fuel into the cylinders of the engine 2 to increase the temperature of the additional catalyst 26, according to a second mode of operation, when the value of [...] 1 is greater than the threshold of TADOC 1;
• a control step of the system 32 for injecting fuel into the exhaust line when the value of the catalyst 2 [...] filtering system is greater than the threshold tadoc2.

The method may also comprise a step of measuring the value of tsdoc1.

The first mode of operation of the system 10 injection into the cylinders of the engine 2 8 may include shifting the main injection of fuel. The system may increase the amount of fuel injected to keep the torque value requested by the user of the vehicle. In this first mode of operation, the injection system 10 can also be a "post-injection" close. By "post-injection" is meant near an additional fuel injection which occurs before anglePredetermined crank. The fuel in the additional fuel injection burns in the cylinders of the engine 2.8 this first mode of operation may utilize either the offset of the main injection, post injection is near, or both together.

In this first mode of operation of the injection system, it is question of raising the exhaust gas temperature upstream of the oxidation catalyst 26 additional, in particular for the latter reaches its activation temperature, temperature for the oxidation of the gasified fuel.

When the value of [...] 1 supplied by the temperature sensor 36 is greater than the threshold of TADOC 1 for activation of the additional oxidation catalyst 26, the system 10 injection can be controlled according to a second mode of operation. In this mode of operation, the system 10 can perform injection "post-injection" remote, [...] to say a supplementary injection which occurs after a predetermined crank angle. The fuel in the additional fuel injection does not burn in the cylinders 8 of the engine 2, but it will be gasified and will burn through the oxidation catalyst 26. This increases the temperature of the oxidation catalyst 26 and the additional gas from the catalyst 26. In the second operation mode, the system 10 can accomplish this injection post-injection far further injections described in the first mode of operation.

With the device and its method, it is thus possible to warm the exhaust gas upstream of the oxidation catalyst 28 placed in the filtration system a much larger than in the known methods and devices. This is advantageous in particular when the filtering devices are under the floor of the vehicle, because in this configuration the thermal losses in the exhaust gas can prevent the activation of a regeneration.

The additional means for heating the exhaust gas upstream of the oxidation catalyst 28 may comprise a system for increasing the load on the engine. ThisSystem includes an alternator (not shown), driven by the motor, which supplies electrical energy consuming sources. The sources energy consuming may include, without limitation, immersion heaters 50 warming the coolant of the engine. The unit 41 controls the activation of one or more immersion heaters as required by a load to be applied. The load applied on the engine results in a criterion of load applied to the alternator, for example 90% of the total capacity of the alternator. The cleaning method may also include a step of activating the criterion of minimum load to be applied to the engine, using the system to increase the load on the engine.

This system to increase the load on the engine is used primarily when the engine is at idle and at very low loads.

The sources energy consuming electrical system may include an exhaust gas heating (not shown). The system is placed in the exhaust line 14 upstream of the oxidation catalyst 28. II can also be placed upstream from the additional catalyst 26. The advantage of this source consuming energy is what increases the load on the engine to increase exhaust temperature and also directly heat the exhaust gas.

With these additional means, it is possible to activate a regeneration regardless of engine operating conditions.

However, in order not to activate regeneration at times that would not be expedient for the motor, the device may comprise means for measuring the temperature of the engine. The unit 41 receives the temperature information of the cooling liquid of the engine from a sensor 51 and compares it to a threshold value. This means avoids activating a regeneration when the engine is cold, because it could damage the transistor.

Similarly, in order not to the driving pleasure, the device may comprise means for measuring the speed of theVehicle. The unit 41 receives information from the sensor (not shown) of vehicle speed, and compares it to a threshold value. This means may, for example, avoid activating a regeneration when the vehicle is stationary.