More specifically, the subject of the invention is a process comprising the operations of generating, by indicator means, electrical signals indicative of the values of operating parameters of the engine; and controlling, by processor and control means, the injectors of the engine in a predetermined manner as function of the signals provided by the said indicator means, in such a way as to cause an increase in the temperature of the exhaust gas so as to result in combustion of the particulates accumulated in the filtration device or filter.

Processes of this type are known which make it possible to control the regeneration of the filtration device (so-called "trap"for the particulates) according to strategies based on the distance travelled by the motor vehicle and on a counter pressure signal provided by a sensor installed in the exhaust duct.

One object of the present invention is to provide an improvised process for the regeneration of such a filtration device.

This object is achieved according to the invention with a process the salient characteristics of which are defined in the annexed Claim 1.

Further characteristics and advantages of the invention will appear from the following detailed description, given purely by way of non-limitative example, with reference to the attached drawings, in which : Figure 1 is a schematic representation of a system operating according to the invention; Figure 2 is a graph which qualitatively shows, as a function of the speed of rotation n of the engine plotted on the abscissa, the quantity q of fuel injected into the engine, for various types of journey or trip of a motor vehicle; Figure 3 is a block diagram which illustrates a way of controlling the quantity of fuel injected into the cylinders of the engine in a post-injection phase; and Figure 4 is a further diagram which shows the variation of a function which represents the concentration of the particulates in a filter during a regeneration phase as a function of the working regeneration time t*, plotted on the abscissa.

With reference to the drawings, the reference letters ICE in Figure 1 generally indicate an internal combustion engine, for example a diesel cycle engine. In the illustrated example this engine comprises four cylinders C1-C4 disposed in line, but the invention is not limited to this configuration.

Each of the cylinders of the engine ICE is associated with a respective injector 11-14 controlled by an electronic unit ECU. The engine ICE has an exhaust manifold EP in which, in the illustrated example, and in a manner known per se, are located first and second catalytic converters, CC1 and CC2.

The second catalytic converter, which is disposed downstream of the first, is associated with a particulate filtration device indicated PT. An electric temperature sensor TS is associated with the inlet of the filter PT to provide, in operation, electrical signals indicative of the temperature of the exhaust gas at the inlet of this filter.

The sensor TS is connected to an electronic processor and control until PCU. In the exemplary embodiment illustrated in Figure 1 this unit PCU is shown as a separate and distinct unit from the unit ECU which controls the engine injectors.

It will however be apparent to the man skilled in the art that in place of two physically separate, although interconnected, units it is possible to utilise a single electronic unit arranged to perform the functions of both units ECU and PCU.

Connected to the unit PCU are further devices S1-S5, which provided with electrical signals indicative of the speed of rotation n (number of revolutions in unit time) of the engine ICE, the quantity q of fuel injected into the cylinders of the engine ICE, the temperature Tc of the coolant liquid of the engine ICE, the atmospheric pressure P and temperature TA of the aspirated air.

Associated with the unit PCU there are further memory devices M. Although in Figure 1 these memory devices are illustrated as separate from the unit PCU it will be apparent to the man skilled in the art that such memory devices could be integrated into the memory PCU or even into the unit ECU.

The processor and control unit PCU is arranged to perform, in cooperation with the unit ECU, phases of regeneration of the filter PT by controlling the injectors I1-A4 in a predetermined manner and as a function of the signals provided by the devices S 5 and TS, in such a way as to cause a controlled increase of the temperature of the exhaust gas so as to cause combustion of the particulates accumulated in the said filter.

In the above-described process the processor and control unit PCU is, for this purpose, in particular arranged to identify in operation the type of journey or trip which the motor vehicle is making at any time, from among a plurality of predefined types of journey or trip. The identification of the type of journey or trip is made on the basis of signals provided by the devices S1 and S2, that is as a function of the instantaneous speed of rotation n of the engine ICE and the quantity q of fuel injected into the said engine.

The type of trip or journey which the motor vehicle is making is determined on the basis of the results of a statistical analysis, and on the basis of a diagram such as the qualitative diagram illustrated in Figure 2. In this Figure the quantity q of injected fuel is plotted along the ordinate as a function of the speed of rotation n of the engine. In this Figure the curve indicated A is the curve corresponding to the operating condition of the engine with the accelerator pressed 100%, that is the curve corresponding to the maximum delivery of power by the engine ICE.

The region underlying the curve A is divided (on the basis of experimental trials) into a plurality of ranges of values each corresponding to a particular type of journey or trip profile of the motor vehicle. In the illustrated example are indicated substantially four ranges indicated MP1-MP4 and corresponding, in order, to a city journey or trip ("urban driving"), to a mountain journey, to motorway driving and, finally, to the so-called mixed journeys.

A diagram of the type illustrated by way of example in Figure 2 is memorised in the system, for example in the memory devices M associated with the unit PCU, for example in the form of a table or map. In operation, the unit PCU is arranged to acquire the signals indicative of the speed of rotation n and of the quantity q of injected fuel, and to average the corresponding values acquired, for example every 20ms in a movable temporal window of, for example 5 minutes.

On the basis of the averaged values thus obtained the unit PCU determines the type of journey or current trip profile MPi (i = 1,..., 4 in the example of Figure 2).

The processor and control unit PCU is further arranged to calculate, by means of a predefined estimation function, and in dependence on the type of journey or trip MPi, the quantity of particulates Q gradually accumulated in the filter PT, and to start a filter regeneration phase when the quantity of particulates accumulated in the filter, as thus calculated, exceeds a predetermined threshold.

The unit PCU in particular is arranged to calculate the quantity Q of particulates accumulated in the filter PT on the basis of a predetermined function I, indicative of the rate of accumulation (for example in g/h) of the particulates in the filter PT, predetermined and memorised for the said types of journey or trip, MPi of the motor vehicle. In this way it is found that the accumulation of the particulates in the filter is an essentially linear process in time, in dependence on the different conditions of use of the engine of the motor vehicle, that is to say for the different types of journey or trip profile in which the motor vehicle is used. The function I=I (t, MPi) is conveniently determined in a statistical manner and is memorised in the system as a function of the different types of trip of the vehicle.

In operation, the quantity Q of particulates accumulated at each instant is then calculated by the unit PCU as an integral over time of the various rates of accumulation, upon variation of the type of journey or trip profile of the vehicle, essentially according to the relation of the type: where t is time, and Qo represents the so-called initial condition determined by the quantity of particulates remaining in the filter PT at the end of the preceding regeneration phase.

When the quantity Q of particulates accumulated exceeds a predetermined threshold the unit PCU causes commencement of a new regeneration phase.

Conveniently, the comparison threshold is predetermined with prefixed values in dependence of the type of journey or trip in which the motor vehicle is engaged at the time.

In the regeneration phase spontaneous combustion of the particulates takes place as soon as and as long as the exhaust gas of the engine at the inlet of the filter itself reaches temperatures greater than a predetermined value, for example 650°C, in the presence of a sufficient percentage of oxygen. The processor and control unit PCU is arranged to provide closed loop control, during a filter regeneration phase PT, of the temperature in the filter itself, causing a controlled increase of the temperature of the exhaust gas to result in combustion of the accumulated particulates accumulated in the filter.

The control of the temperature during the regeneration process of the filter PT can take place conveniently as shown in the diagram of Figure 3. In conformity with this diagram the unit PCU is arranged to cause, in an open loop process, a partial quantity PIQ of fuel to be injected in the cylinders C1-C4 of the engine ICE in a post-injection phase as a function of the speed of rotation n of the engine and the overall quantity q of fuel to be injected into the cylinders at each injection. The determination of the partial quantity PIQ of fuel to be injected in the post-injection phase is determined for example by means of a map (PIQ map) stored in the memory devices M.

The unit PCU is further arranged to modify the said partial quantity PIQ of fuel to be injected into the engine in the post injection phase by adding or subtracting a first correction of quantity APIQ1, determined according to a mapped function of the speed of rotation n of the engine and the quantity q of fuel injected into the cylinders, and "weighted"as a function of the values assumed by some ambient quantities (such as the air temperature TA and the atmospheric pressure P) and engine quantities (such as engine coolant temperature Tc), through a factor W1 obtained by means of a suitable pre-memorised weighting map. Quantity PIQ is further modified by adding/subtracting to or from it a second correction quantity APIQ2 determined in a closed loop manner as a function of the difference between the effective temperature T of the exhaust gas at the inlet of the filter PT (detected by means of the sensor TS) and a predetermined reference temperature T, P. The correction quantity of APIQ2 can conveniently be determined by means of a PID governor (Proportional-Integral Derivative).

Subsequently, following a further conditioning through a factor W2 obtained from a suitable map as a function of the value of the exhaust gas temperature T there is obtained the effective partial quantity APIQ of fuel to inject into the engine in the post injection phase during the filter regeneration process.

The processor and control unit PCU is arranged to terminate a filter regeneration phase of the filter PT after a predetermined working time t* from initiation of this regeneration has elapsed, which time is conveniently variable in a predefined manner as a function of the type of journey or trip MPi performed by the motor vehicle during the regeneration. The working time t* is defined as the percentage of time for which the temperature in the filter PT is effectively greater than the predetermined value (for example 650°c).

The unit PCU is moreover arranged to calculate, at the end of the filter regeneration phase, the residual quantity Qo of unburnt particulates in the filter, according to a further predetermined estimation function, and to assume this residual quantity as initial value for the calculation of the quantity of particulates accumulated in the filter starting from the end of this regeneration phase.

The quantity of residual particulates at the completion of regeneration is conveniently calculated in a manner which varies as a function of the type of journey or trip undertaken during regeneration.

If a regeneration phase is interrupted the residual particulates can be calculated on the basis of an estimation function such as that (essentially decreasing exponential) which is qualitatively shown in Figure 4.

In this Figure this rate of percentage decrease I* of the particulates in the filter during regeneration is plotted along the ordinate, with reference to the variation of working regeneration time t* which is plotted on the abscissa.

This function can be utilised in particular also to estimate the residual quantity of unburnt particulates in the filter PT when, during a regeneration phase of the filter, the engine ICE is switched off before completion of this regeneration phase.

Naturally, the principle of the invention remaining the same, the embodiments and details of construction can be widely varied with respect to what has been described and illustrated purely by way of non-limitative example, without by this departing from the ambit of the invention as defined in the annexed claims.