Method for controlling the regeneration process in lnt devices   

Abstract: A method is provided for controlling the regeneration process of a LNT device for the treatment of exhaust produced by an internal combustion engine. The method includes, but is not limited to storing a plurality of parameters in the form of preset values which relate to admissible regenerating conditions, receiving a regeneration request, measuring the current values of the parameters to define the current operating conditions of the engine and the LNT device, comparing the current values with the preset values of a corresponding parameter to evaluate if the current operating conditions of the engine and of the LNT device satisfy the admissible regenerating conditions for carrying out the regeneration process, and inhibiting the regeneration process if at least one current value of a corresponding parameter does not satisfy the admissible regenerating conditions for carrying out the regeneration process.

This application claims priority to British Patent Application No. 1021072.2, filed Dec. 13, 2010, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The technical field relates to exhaust after treatment for internal combustion engines having lean NOx trap (LNT), and more specifically relates to a method for controlling the regeneration process of the LNT device.

Several solutions have been proposed for controlling NOx emission, in particular for diesel-powered engines. In fact, as well known, diesel engines are operated at high air to fuel ratios, usually higher than the stoichiometric air to fuel ratio, in order to reduce fuel consumption. This type of engines, called “lean burning” engines, produce exhaust with high content of oxygen and of nitrogen oxides (NOx).

The Lean NOx Trap systems (LNT) are devices used for removing NOx from the vehicle exhaust and, more in detail, LNTs adsorb NOx under lean operation of the engine and reduce the adsorbed NOx under rich operation condition. In other words, during the lean operation of the engine, the LNT adsorbs and stores the nitrogen oxides from the exhaust, typically NO and NO2, and the stored NOx are reduced during a regeneration process, or de-nitration phase, during which the engine is operated in a rich combustion condition. The rich operating, or combustion, condition is obtained by a special management and control of the air and fuel delivered to the engine.

For controlling a LNT device, it is useful to regulate the frequency with which the rich combustion conditions are created and the regeneration process is performed. For this purpose, methods have been proposed for scheduling the LNT regeneration including periodic regeneration, or based on the LNT loading. It should be noted that all these methods have the object to reduce the fuel penalty for regeneration and the operating cost of the vehicle. In fact, when it is necessary to carry out the regeneration process in order to reduce the stored NOx, it is useful to evaluate if the system is in the proper conditions to allow the transition from a lean to a rich combustion conditions, which is necessary to perform the regeneration process. Rich combustion mode is not possible under every operating conditions of the vehicle, without creating undesired problems, specifically relating to the temperature and combustion instability.

In view of above, there is at least the need to control system conditions after the regeneration request has been triggered in order to reduce operating costs of the vehicle and without affecting the customer feelings during vehicle use. There is at least another need for a continuous control of the system status after the regeneration has been started, in order to evaluate if the system conditions are changed and are switching in operative condition where the regeneration is not allowed. More in detail, during the everyday real driving conditions, it could happen that a regeneration process is started (under adapted system conditions) but it cannot be concluded because a changing in the system conditions, for example the engine switching from one condition where the rich combustion mode is allowed to another one where it is unstable or it is not allowed.

Therefore, at least one object is to provide a method for controlling the LNT regeneration process depending on the system conditions. As will be disclosed in detail, “system conditions” on which the inhibition of the regeneration phase is based comprise not only LNT conditions and its status, but also engine conditions, environment conditions, etc. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.

SUMMARY

A method is provided for controlling the regeneration process of a LNT device for the treatment of exhaust produced by an engine. The method comprises the steps of defining and storing a plurality of parameters in the form of preset values which relate to admissible regenerating conditions; receiving a regeneration request; measuring the current values of said parameters to define the current operating condition of the engine and the LNT device; comparing the current values with the preset values to evaluate if the current operating condition of the engine and of the LNT device satisfy the admissible regenerating conditions for carrying out said regeneration process, and inhibiting the regeneration process if at least one current value of a corresponding parameter does not satisfy the admissible regenerating conditions.

It should be noted that the term “controlling” is used to indicate that the LNT regeneration process can be inhibited, i.e., prevented or interrupted. In other words, the method is intended to prevent starting of the regeneration process depending on the system conditions following a regeneration request, or to interrupt (i.e., stopping a regeneration phase which has been started before) if the system conditions are changed and are no longer suitable for carrying out the regeneration of the stored NOx. Thus, when the measured values do not satisfy the admissible regenerating conditions, a new regeneration process is not started, and a regeneration process already started is interrupted.

More in detail, after receiving a regeneration request, generated by a subsystem based on known criteria and control strategies, the current values of different parameters are measured in order to define the current operating system conditions. Then, the measured values are compared with the preset values of the parameters to evaluate if the current system conditions satisfy the admissible regenerating system conditions for performing the regeneration process. If at least one of the measured values of the parameters does not satisfy the preset value of the parameters, which represents admissible regenerating system conditions, the regeneration process is inhibited. Accordingly, to a preferred embodiment of the method, steps are repeated during the regeneration process.

Controlling system conditions at the request of regeneration, and during the regeneration process, allows evaluating in accurate manner, taking into account current operating conditions, if the regeneration process can be started or a regeneration process that has been already started before can be continued. The admissible regenerating conditions comprise at least one preset value, or range of values, of a plurality of parameters, comprising at least the engine temperature parameters, ambient condition parameters, lambda sensor condition parameters, transition state condition parameters, and engine condition parameters. More in detail, in order to identify admissible regeneration conditions are evaluated also operative condition of the engine and the measured values of lambda sensors for checking their availability.

It should be understood that above-mentioned parameters allow defining a system status (or condition) of the LNT device, of the engine, of the ambient, and of the vehicle in order to control in accurate and efficient manner the regeneration process of the LNT device. Moreover, it is to be noted that the term “values” is herein used not only to indicate a single value or a range of values of the aforementioned parameters, but also to indicate some “variables” which can be used to evaluate system conditions.

Advantageously, carrying out the regeneration process only during admissible system conditions, i.e., during admissible regenerating conditions, improves system efficiency, customer feeling, and combustion stability and does not adversely affect the fuel consumption. Moreover, the controlling method allows avoiding undesired loss or increase of the torque exerted by the engine that adversely affects the customer feeling during the vehicle use.

Although LNT devices are used in vehicles having diesel engines, it should be noted that the method is not limited to this implementations. The method is suitable to be applied also in LNT regeneration devices in connection with engines powered by other types of fuel.

Another embodiment provides a computer program comprising computer executable codes for carrying out the method for controlling the regeneration process of a LNT device for the treatment of exhaust produced by an engine, described above. The computer program, stored in a computer readable medium includes: computer executable code for: receiving a regeneration request; a computer executable code for measuring the current value of the parameters to define the current operating conditions of the engine and the LNT device; and computer executable code for comparing said current value with preset value of a corresponding parameter to evaluate if the current operating conditions of said engine and said LNT device satisfy said admissible regenerating conditions for carrying out said regeneration process and for inhibiting said regeneration process if the current value of a corresponding parameter does not satisfy said admissible regenerating conditions for carrying out the regeneration process.

A further embodiment relates to an apparatus for controlling the regeneration process of a LNT device for the treatment of exhaust produced by an internal combustion engine, the apparatus comprising: means for defining and storing a plurality of parameters in the form of preset values which relate to admissible regenerating conditions; means for receiving a regeneration request; means for measuring the current values of said parameters to define the current operating conditions of said engine and said LNT device; means for comparing said current values with the preset values of a corresponding parameter to evaluate if the current operating condition of said engine and said LNT device satisfy said admissible regenerating conditions for carrying out said regeneration process, and means for inhibiting said regeneration process if at least one current value of a corresponding parameter does not satisfy said admissible regenerating conditions.

Advantageously, carrying out the regeneration process only during admissible system conditions, i.e., during admissible regenerating conditions, improves system efficiency, customer feeling, and combustion stability and does not adversely affect the fuel consumption. Moreover, the controlling method allows avoiding undesired loss or increase of the torque exerted by the engine that adversely affects the customer feeling during the vehicle use.

An embodiment of the apparatus furthermore is configured to repeat steps during the regeneration process. Controlling system conditions at the request of regeneration, and during the regeneration process, allows evaluating in accurate manner, taking into account current operating conditions, if the regeneration process can be started or a regeneration process that has been already started before can be continued.

Another embodiment of the apparatus is configured to use temperature parameters selected among the cooling fluid temperature, the engine metal temperature, the exhaust temperature upstream and/or downstream of the LNT device, and the temperature upstream of the turbocharging as said parameters and has means for inhibiting which are configured to inhibit the regeneration process if the current value of at least one of said temperature parameters is outside a preset range. An apparatus configured in this way defines a system status (or condition) of the LNT device, of the engine, of the ambient, and of the vehicle in order to control in accurate and efficient manner the regeneration process of the LNT device.

A further embodiment of the apparatus is configured to use ambient condition parameters including the ambient temperature and the ambient pressure as said parameters, and has means for inhibiting which are configured to inhibit the regeneration process if the current value of the ambient temperature is outside a preset range or if the current value of the ambient pressure is outside a preset range.

Another embodiment of the apparatus is configured to use lambda sensor condition parameters as said parameters, and has means for inhibiting being configured to inhibit the regeneration process if the current value provided by said lambda sensor is outside a preset range.

Another embodiment of the apparatus is configured to use transition state parameters as said parameters, and wherein the means for inhibiting are configured to inhibit if the current transition time is above a preset value.

Another embodiment is configured to use engine condition parameters including the rotation speed and the torque of the engine as said parameters, and wherein the means for inhibiting are configured to inhibit the regeneration process if the current value of at least one of said engine condition parameters is outside a preset range.

Still another embodiment if the apparatus has means for defining and storing said engine condition parameters for each gear.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and:

FIG. 1 is a flow chart of the complete logic overview of the method for controlling the regeneration process according to an embodiment;

FIG. 2 is a flow chart of the control strategy of the temperature condition parameters in the method according to an embodiment;

FIG. 3 is a flow chart of the control strategy of the ambient condition parameters in the method according to an embodiment;

FIG. 4 is a flow chart of the control strategy of the engine condition parameters in the method according to an embodiment;

FIG. 5 is a flow chart of the control strategy of the lambda sensor availability in the method according to an embodiment;

FIG. 6 is a flow chart of the control strategy of the lambda conditions during the regeneration phase in the method according to an embodiment; and

FIG. 7 is a simplified block diagram of vehicle including an internal combustion engine and an exhaust after treatment LNT device controlled according to the method of an embodiment.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description.

The method for controlling the regeneration process of an LNT device for the treatment of exhaust produced by an engine is based on the comparison between the current operating system conditions, i.e., current operating conditions of the LNT device and the engine, and the admissible regenerating conditions for carrying out the regeneration process.

According to an embodiment for the controlling method, steps of measuring of the current parameters values and the comparison step with the preset values are performed also during the regeneration process. Thus, it is possible to evaluate real-time changing in the current operating system conditions, in order to interrupt a regeneration process if the measured values of the parameters do not satisfy the preset values.

As seen in FIG. 1, the complete logic overview of the method for controlling the regeneration process is illustrated. In the left portion of FIG. 1 are represented the phases during which the system conditions are determined, while on the right side of the figure are schematically indicated the parameters controlled in each phase in order to establish the current operating system conditions. The flow diagram shows all the phase during which the controlling method 10 is carried out, from the demand of regeneration to the execution of said regeneration process, passing through a transition phase in which the system is switching between a lean and rich combustion conditions.

More in detail, a signal of regeneration demand is generated, see block 11, from a subsystem, which is based on known criteria and control strategy, then the decision block 12 determines if the regeneration is allowed depending on the measured values of a plurality of parameters representing the current operating conditions. As it will be explained later, parameters regarding the system conditions are measured all together, and in real time, and are compared to correspondent preset values in order to establish if the system is in the proper (admissible) condition for carrying out the regeneration process.

As described above, the parameters measured and compared with the correspondent preset values after receiving the regeneration request are at least the engine temperature condition parameters, ambient condition parameters, lambda sensor condition in order to evaluate its availability, and engine condition parameters (see block 5). If the measured values for at least one of the parameters, when compared with the correspondent preset values, do not satisfy the admissible regenerating system condition defined by the parameters preset values, the regeneration is not allowed, see block 12′, and the controlling method returns to the initial block 11 until a new request of regeneration is generated. If all the measured values of the checked parameters satisfy the admissible regenerating system conditions adapted for carrying out the regeneration process, defined by the correspondent preset values, the regeneration process is started and the engine is involved in a transition phase between lean and rich combustion conditions, see block 13.

The engine transient, or transition phase, is a period over which the engine operating (combustion mode) is changing, i.e., the engine is controlled in order to pass from a lean combustion mode to a rich combustion mode in which the regeneration has to be performed. During the engine transient, i.e., the period used for passing from the lean mode to the rich mode, all the parameters already measured and compared after the regeneration demand are measured in real time and compared to preset values. Continuous controlling of the plurality of parameters, by measuring current values and comparing with the preset values, allows evaluating if the system conditions are changed and if the current operating conditions are adapted to perform the regeneration process. As illustrated in the block 6, during the transition phase the method comprises also the step of measuring and comparing the values of the parameters relating to the lambda sensor condition during transition phase between lean and rich combustion conditions, in order to evaluate if the transition phase is concluded and the rich conditions are reached. It should be noted that the detection of the engine transient is carried out by at least a lambda sensor by means of which it is also carried out the control of the time delay in the transition phase for arriving from the lean to the rich condition (see decision block 14).

If at least one of the current measured values does not satisfy the preset values, and the regeneration request is still active, the regeneration process is interrupted (block 15 and 16) and the method returns to the initial block 11. If all the measured values of the parameters, when compared to the preset values, satisfy the admissible system conditions, the regeneration process reach the steady state in which the stored NOx are reduced and the engine is in the rich combustion mode (see block 17). In addition, during the steady state of the regeneration process, parameters are measured and compared with the preset values as shown in the block 7; also, lambda values during the steady state are measured and compared with the preset values in order to evaluate if the rich combustion conditions are maintained (block 17′). In other words, during the steady state of the regeneration process, lambda sensor is used for controlling whether the rich combustion conditions are maintained.

If the preset values of the parameters representing admissible conditions for regeneration are not satisfied, or if the regeneration request in no longer active, the regeneration process is aborted, as indicated in blocks 18 and 19. In decision block 17′ and 18, if the current operating state of the system conditions satisfy the admissible regenerating system conditions, and the regeneration request is still active, the regeneration process is continued and a continuous control (measurement and comparison) of the parameters are performed until the regeneration process is terminated, i.e., the request of regeneration is not active, or until at least one of the measured values of the parameters does not satisfy the preset values. In the latter cases, the method for controlling returns to the initial block 11.

As mentioned above, according to an embodiment, the parameters are measured in real time. As already stated, the system conditions after the regeneration request are detected by means of parameters that comprise the temperature conditions, ambient conditions, lambda sensor conditions, transition state conditions, and engine conditions.

Now, with reference to FIG. 2 to FIG. 6, the control strategy of the above-mentioned parameters will be disclosed in detail. According to an embodiment of the method, parameters relating to the temperature conditions are selected among the cooling fluid temperature, engine metal temperature, exhaust temperature upstream and downstream of the LNT device, and temperature upstream of the turbocharging.

As known in the field, adapted sensors 110-113 (see FIG. 7) are mounted on the engine, upstream and downstream of the LNT device in order to provide a signal with the current measured temperature values of the cooling fluid (or water) temperature, engine metal temperature, exhaust temperature upstream and downstream of the LNT device and temperature upstream of the turbocharging. The regeneration process is inhibited if at least one of the temperature values does not satisfy the admissible system conditions for the regeneration represented by the preset temperature values.

FIG. 2 shows the flow chart of the temperature condition control, the method is performed by a control unit 105 (see FIG. 7) which uses input from temperature sensors 110-113 used for measure the temperature values of the water, engine metal, exhaust temperature upstream and downstream of the LNT and temperature upstream of the turbocharging. The control unit 105 using the current measured temperature values to determine whether the values are below or above preset values, in other words, the control module compare the measured temperature values with a low and high correspondent values in order to detect whether the temperature is within a predetermined range. It should be noted that all the temperature values could be determined by means of alternative sensors or additional ways, such as models, or by combination of input from sensors and models.

Referring now to FIG. 2, after receiving a regeneration request, see block 21, each decision block 22-25, respectively evaluates whether the water temperature is within the range defined by a high value c1 and a low value c2. If the current measured value of the water temperature is above the preset value c1 or below the preset value c2, the admissible regenerating system conditions are not satisfied, i.e. the measured value is outside the preset range, and the regeneration is not allowed, see block 29. In the same manner, the method compare other measured temperature values with the preset ranges of values, see blocks 23-26. If all the measured temperature values are within the preset ranges, i.e., the admissible regenerating system conditions for performing regeneration process are satisfied, the regeneration process is allowed (see block 27), and the measure and the comparison of the temperature values continue until the requirement are no longer satisfied (see blocks 22′-26′) or the request of regeneration is no longer active, as clearly shown in decision blocks 28 and 29.1.

FIG. 3 discloses the control strategy of the ambient condition parameters, which comprise at least the ambient temperature and the ambient pressure. The regeneration process is inhibited if at least one of the current values of the parameters relating to the ambient conditions, when compared to the correspondent preset values, does not satisfy the preset values defining the system conditions adapted for carrying out the regeneration process of the LNT device. Preferably, the regeneration is not allowed if the measured values of the ambient temperature is outside a present range of values or the measured values of the ambient pressure is outside a present range of values.

After receiving a request of regeneration (block 31) a control unit 105 uses inputs from temperature and pressure sensors 120, 121 (see FIG. 7) used for measuring the current ambient temperature value and the current ambient pressure value. The control unit 105 uses the current measured ambient temperature value to determine whether the value is below or above preset values, namely ambient temperature values with a low c12 and high c11 correspondent values in order to detect whether the temperature is within a predetermined range (see decision block 32). In the same way, as represented in the decision block 33, the control unit 105 compares the measured ambient pressure in order to detect whether the ambient pressure is below or above preset values, namely ambient pressure values with a low c14 and high c13 correspondent values in order to determine whether the pressure is within a predetermined range.

If the current measured value of the ambient temperature is not within the range values c11-c12, or the ambient pressure is not within the range values c13-c14, the current operating conditions are not in the admissible system conditions adapted for performing the regeneration process: thus the regeneration is not allowed (see block 34) and the method returns to the initial block 31. On the contrary, if all the measured values satisfy the aforementioned conditions of decision blocks 32 and 33, a new regeneration process is started, see block 35. In the latter case, the steps of measuring and comparing the ambient condition values continue until the requirement are no longer satisfied (see blocks 32′ and 33′), or the request of regeneration is not active, as clearly shown in decision blocks 36 and 37.

As already mentioned above, the controlling method is also based on the engine condition parameters in order to prevent or interrupt the LNT regeneration process. In fact, not all the engine operative conditions allow the regeneration process without adversely affecting the fuel consumption or the costumer feeling, for example, by undesired drop or change of the exerted torque. According to the controlling method, engine conditions parameters include at least engine rotation speed, load (torque) and gear, and the regeneration process is inhibited if the current value of these engine parameters is outside a preset range. In fact, there are engine operating conditions where the engine rotation speed, torque, and gear do not allow performing the LNT regeneration process and a new regeneration process is not allowed to start or, if the regeneration has already been started, it shall be interrupted. In the step of evaluating the parameters relating to the engine conditions, torque and engine speed indications present in the control unit 105 can be evaluated by models or sensors.

As shown in FIG. 7, sensor 130 is provided for measuring the engine rotation speed. It should be noted that, terms “measuring” and “evaluating” values of said parameters are herein used with the same meaning. In fact, as already mentioned, values could be measured directly by adapted sensors or evaluated in alternative ways such models, or by combination of input from sensors and models. The control unit 105 compares the measured or evaluated values with correspondent preset values and evaluate whether the admissible system conditions for performing the regeneration process are satisfied. According to an embodiment, for each gear of the transmission system of the vehicle is possible to define preset values of engine rotation speed and torque in which the regeneration process is allowed.

FIG. 4 shows graphically the control strategy based on the rotational speed, torque, and gear indication present in the control unit. In the graph of FIG. 4, valid for a single gear, the preset values form a region A of both rotational speed and torque where the regeneration process is allowed. The preset values of rotational speed and torque of the region A could be defined by the intersection of two maps of the rotational speed and torque for each gear.

FIG. 4, also shows a second region B of rotational speed and torque values, which is defined by the intersection of other two maps of the rotational speed and torque for each gear. The region B has a greater extension than region A and defines a hysteresis window for controlling the regeneration process. As will be described later, region B allows to define a plurality of preset values in which the admissible regenerating system conditions are not satisfied, thus a new regeneration process shall be not allowed, but a regeneration process already started can be continued.

The control unit detects whether the measured, or evaluated, values of the engine speed and torque are inside one of the regions A and B represented in FIG. 4. If the measured values are in the region A, the regeneration is allowed or can be continued, while the current measured values of the engine rotational speed and torque fall in region A or region B. If the measured values are in the region B and the control unit receives a regeneration request, the regeneration phase is not permitted, and a subsequent regeneration process shall be started only if the measured values fall in the region A. In other words, the regeneration phase starts only if the measured or evaluated current values fall in region A and it can be continued also if said current measured or evaluated values fall in region B. Outside from region A the regeneration phase cannot be started.

As already mentioned above, the controlling method is based on parameters relating to the lambda sensor condition, and the regeneration process is inhibited if the current value provided by a lambda sensor 150 and/or 151 (see FIG. 7) is outside a preset range. FIG. 5 shows a flow chart of the control strategy of the lambda sensor availability in the controlling method. Lambda sensor availability is checked by means of the current measured value of at least one lambda sensor, which is compared to a preset value, or range of values, to evaluate if that lambda sensor is in operation. Usually, a first lambda sensor 150 is disposed upstream of the LNT device 102 and a second lambda sensor 151 is disposed downstream of the same LNT. Both first and second lambda sensors are provided to send signals to the control unit 105 relating the operating air/fuel mixture ratio upstream and downstream of the LNT.

As illustrated in FIG. 5, after a request of regeneration 51, the measured values from lambda sensors 150, 151 respectively upstream and downstream of the LNT device 102 are compared to preset values, or range of values, in decision blocks 52 and 53 in order to evaluate if the lambda sensors are available. In other words, the current measured values of lambda sensors are used to establish if the lambda sensors are in operating conditions; for example, in case of failure of a lambda sensor, the measured values compared to the preset values allow to determine the unavailability of the probe.

If at least one of the measured values does not satisfy the preset values, the regeneration is not allowed, see block 54. On the other hand, if both lambda sensors are available, the regeneration is allowed (block 55). In decision block 56, the control unit allows continuing the regeneration in the case the regeneration request is still active; on the contrary, if these conditions are not satisfied, the regeneration is aborted and the control method returns to the initial block 51. The controlling method uses the measured values obtained from the lambda sensors 150, 151 in order to evaluate if the system is in the transient state between lean and rich conditions and/or if the rich combustion conditions are reach and maintained during the steady state of the regeneration process. In fact, as already mentioned above in connection to FIG. 1, if all the measured values of the checked parameters satisfy the admissible system conditions adapted to carrying out the regeneration process defined by the correspondent preset values, the regeneration process is started and the engine is involved in a transition phase between lean and rich combustion conditions. It should be understood that the measured value of at least one lambda sensor that is compared to a preset value, or range of values, is used to evaluate if the system is in the transient state between lean and reach conditions.

Preferably, the lambda sensor disposed upstream of the LNT device is used. In other words, measuring and comparing the lambda values during the transition phase allows evaluating if the rich conditions are reached. During the steady state of the regeneration process, the measured value of at least one lambda sensor is compared to a preset value, or range of values, to evaluate if the system is in the rich combustion conditions.

FIG. 6 shows the flow chart of the control strategy based on condition control of the lambda sensors during the transition state and steady state of the regeneration process. After a regeneration request, parameters are measured and compared in order to evaluate if the regeneration process can be allowed, see blocks 61, 62 and 62′. If all the parameters satisfy the preset values, as disclosed above in connection to FIG. 2 to FIG. 4 the regeneration process is started and the system, and more particularly the engine, is involved in a transition phase (state) between lean and rich combustion conditions (block 63). It should be noted that the detection of the transient state is carried out by lambda sensors 150 and 151, by means of which it is also carried out the control of the transition time between lean and rich conditions.

Decision block 64 counts the time during the transition from a lean to rich combustion modes and, if the time measured is greater than a preset value, the regeneration is inhibited (blocks 65 and 66). According to an embodiment of the controlling method, time delay is counted only if the system is in the transient state.

Parameters used to evaluate if the system is in the transient state between lean and reach conditions comprise the measured value of at least one lambda sensor that is compared to a preset value, or range of values. More precisely, the measured values of the lambda sensors 150 and 151, preferably of the sensor 150 disposed upstream of the LNT device, are compared with a preset range of values defined as a calibrated percentage of a target lambda value which indicate that the transition state is terminated and the system is in the rich combustion conditions. During the transition state, the control unit uses the measured values of lambda to evaluate if the system is in the transient state and the rich conditions are not reached yet.

Other parameters are used to evaluate if the system is in the transient state, and preferably comprise variables which indicate, when compared to a preset value, if the LNT device is in the regeneration phase, e.g., a variable “state” is equal to a preset value and the a “substate” is minor or equal to a preset value. In other words, the current value of a “state” variable and a “substate” variable are used (i.e. measured and compared with a preset value) in order to evaluate if the rich combustion conditions are reached and/or maintained, or if the system is in a transient state between lean and rich conditions.

If the system is in the transient state and the time during the transition from a lean to rich combustion modes is below a preset value c15, the regeneration process can be continued. The timer continues to count until rich conditions are reached (see blocks 67 and 68). As mentioned above, the controlling method allows evaluating if the system has reached the rich combustion conditions by means of parameters including at least variables relating to the state of the LNT device, a “state” variable and a “substate” variable, and the measured value of at least one lambda sensor which is compared to a range of values.

When the measured values of the lambda sensor, preferably of the sensor 150 disposed upstream of the LNT device, are within a preset range of values defined as a calibrated percentage of a target lambda value, the system is in the rich combustion conditions and the regeneration process is in the steady state (block 69). It should be noted that the control of the measured values of the lambda sensor and its comparison with the preset range of values is carried out also during the steady state of the regeneration process until the rich combustion conditions are maintained.

Control of the rich conditions is carried out by means of the variables regarding the LNT device state, and by means of the “state” and “substate” variables. If the current value of the variable “state” is equal to a preset value, and the current value of the variable “substate” is greater than a preset value and minor than another preset value, the LNT device being in regeneration state, measuring of the lambda values and its comparison with a preset range is continued until at least one of the aforementioned conditions are not satisfied. Thus, it is possible to evaluate whether rich combustion conditions are maintained during the steady state of the regeneration process (block 70). It should be noted that the preset range of values defined as a calibrated percentage of a target lambda value, which indicates that the system is in the rich combustion conditions and it is in admissible conditions to perform a regeneration process, can be extended by defining a second range of values having greater limit values. When the current measured lambda value is within the extended preset range, but outside the first preset range of values, a new regeneration process cannot be started but a regeneration process already started before can be continued.

Summarizing, a range of preset values defined as a calibrated percentage of a target lambda value is used to evaluate if the transition phase is terminated, while, during the steady state of the regeneration phase, the measured values of the lambda sensor are compared with another range of two different preset values (also defined as a calibrated percentage of a target lambda value) in order to evaluate if the rich combustion conditions are maintained. As already mentioned above, the second range of lambda values used in the steady state of the regeneration phase is broader than the first range of values used in the transition phase.

The method for controlling the regeneration process of a LNT device for the treatment of exhaust produced by an engine described above, may be carried out by means of a computer program comprising program codes (computer executable codes) for performing the controlling steps already described above in connection to FIG. 1 to FIG. 6. The computer program comprises computer executable codes that can be stored on a computer readable medium, or a storage unit, such as CD, DVD, flash memory, hard-disk, or the like. The computer program comprises computer executable code for receiving a regeneration request; a computer executable code for measuring the current value of said parameters to define the current operating conditions of said engine and said LNT device; and computer executable code for comparing said current value with preset value of a corresponding parameter to evaluate if the current operating conditions of said engine and said LNT device satisfy said admissible regenerating conditions for carrying out said regeneration process and for inhibiting said regeneration process if the current value of a corresponding parameter does not satisfy said admissible regenerating conditions for carrying out said regeneration process.

The computer program further comprising computer executable code for repeating during the regeneration process the execution of said computer program codes in order to repeat steps of the controlling method, during the regeneration process, for evaluating in accurate manner, taking into account current operating conditions, if the regeneration process can be started or a regeneration process which has been already started before can be continued.

It should be noted that the preset values of the parameters, which represent the admissible system conditions for carrying out the regeneration process are stored in a suitable storage unit, or on a computer readable medium, and preferably the computer program according to an embodiment and the preset values of the parameters are stored on the same storage unit or computer readable medium.

FIG. 7 is a simplified block diagram of vehicle including an internal combustion engine 101 and an exhaust after treatment LNT device 102, which can be controlled according to the method described above. Exhaust gases are discharged trough an exhaust manifold 103 connected downstream to a lean NOx trap (LNT) device 102. As already described above in connection to FIG. 5 and FIG. 6, a first lambda sensor 150 is disposed upstream of the LNT device 102 and a second lambda sensor 151 is disposed downstream of the LNT device. Both first and second lambda sensors are provided to send signals relating the operating air/fuel mixture ratio upstream and downstream of the LNT.

A plurality of suitable sensors is provided in order to measure the current value of a plurality of parameters. More in detail, sensors 110-113 are mounted on the engine, upstream and downstream of the LNT device in order to provide a signal with the current measured temperature values of the cooling fluid (water) temperature, engine metal temperature, exhaust temperature upstream and downstream of the LNT device 102, and temperature upstream of the turbocharging. Furthermore, temperature and pressure sensors 120, 121 are provided for measuring the current ambient temperature value and the current ambient pressure value, and sensor 130 is able to measure the engine rotation speed. According to an embodiment, the computer program is stored on storage unit or a computer readable medium that is connected, or integrally produced with an electronic control apparatus for an internal combustion engine 101.

The electronic control apparatus is provided with a microprocessor, or any suitable means known in art, for receiving the computer codes of the computer program and for executing them. Executing these computer codes allows to performing in its totality, or at least in part, the method steps for controlling the regeneration process of a LNT device for the treatment of exhaust produced by an engine described above. The electronic control apparatus can be made as a dedicated piece of hardware, known in the art, such as an Engine Control Unit (ECU) 105, shown in FIG. 7.

Control unit 105 has an internal storage unit on which is stored the computer program allowing to inhibit the regeneration process on the basis of the current value of the parameters received from the sensors. As already explained, the microprocessor of the control unit 105 execute the computer program codes in order to comparing the current measured values of the parameters with a preset value of a corresponding parameter, which is preferably stored in the unit integrated in the control unit, or in a storage unit connected to it, in order to evaluate if the current operating conditions satisfy the admissible regenerating conditions defined by the stored preset parameters values.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.