ENGINE FOR PERFORMING SAID METHOD

TECHNICAL FIELD

The present disclosure is directed to a method for controlling an exhaust treatment system of an internal combustion engine, the exhaust treatment system comprising an exhaust gas passage, an SCR catalyst and a diesel exhaust fluid DEF injection system; and the DEF injection system comprising a DEF tank and being configured to inject DEF in the exhaust gas passage upstream the SCR catalyst.

The present disclosure is further directed to a computer program for performing this method, a computer-readable recording medium containing such computer program, and an internal combustion engine configured to implement this method.

BACKGROUND ART

Engines emit exhaust gas that includes variant components such as hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), etc. An exhaust treatment system can be provided to reduce the levels of HC, CO and NOx in the exhaust gas. The exhaust treatment system may include in particular a selective catalytic reduction (SCR) catalyst. Such an SCR catalyst reduces the NOx content of the exhaust gas.

In addition, a diesel exhaust fluid DEF injection system can be provided to inject a reducing agent (e.g., urea) into the exhaust gas, upstream from the SCR catalyst. The reducing agent forms ammonia that reacts with NOx in the SCR catalyst. The reaction of ammonia and NOx in the SCR catalyst reduces the NOx and results in the emission of diatomic nitrogen and water.

When the outside temperature is very low, the DEF tends to freeze in the

DEF tank. In order to cope with this, the DEF tank is provided with a heater: If necessary, the heater can melt DEF which has frozen in the DEF tank.

In order to maintain the SCR catalyst in good working order (to make sure that the level of NOx in the exhaust gases remains within an acceptable range), it is also necessary to maintain the diesel exhaust fluid DEF injection system in good working order.

Now, if the pump of the DEF injection system is operated (to inject DEF in the exhaust gas) when the DEF tank is completely frozen, no DEF in the liquid state can be pumped. Should this happen, the DEF pump might possibly become drained, and it would become impossible to inject DEF until the DEF pump is primed again.

Provisions are therefore taken to make sure that this never happens.

If the outside temperature is below the freezing temperature of the DEF, a first known solution consists in activating the heater of the DEF tank during a sufficiently long period before starting the engine, to make sure that a sufficient amount of DEF contained in the DEF tank is brought into the liquid state. This solution consumes a lot of energy.

An alternative solution consists, when the temperature is below the freezing temperature of the DEF, to activate the heater upon starting the engine. No DEF injection is made until it is considered that a sufficient amount of DEF has melted and is available to be injected in the exhaust gas treatment system. Consequently, by cold weather the vehicle cannot be depolluted for a relatively long period after starting the engine, which is quite cumbersome.

DISCLOSURE OF THE INVENTION

The object of the present disclosure is therefore to propose a method for controlling an exhaust treatment system of an internal combustion engine, the internal combustion engine being equipped with a SCR catalyst and a diesel exhaust fluid DEF injection system, which method makes it possible to control the exhaust treatment system in an optimized manner, even when the outside temperature is below the freezing temperature of the DEF.

To meet this object, a method for controlling an exhaust treatment system of an internal combustion engine as defined in introduction is proposed.

The control method comprises

51) determining an icing state of the DEF tank; and

52) controlling the exhaust gas treatment system based on an icing state of the DEF tank.

The method comprises two steps SI and S2. During the soaking time of the engine, in step SI the icing state 1% of the DEF tank 40 is determined. Step SI is carried out iteratively so as to calculate at each time step the value of the icing state of the DEF tank.

Then, when the engine is started, step S2 is carried out: The exhaust gas treatment system 20 is controlled based on the icing state 1% determined at step SI.

Since this method comprises a determination of the icing state of the DEF tank, it makes it possible to control the exhaust gas treatment system in an optimized manner. The icing state is defined here as the percentage of DEF which is in the solid state in the DEF tank. Accordingly, the icing state is not a binary information, but an information which can take up several discrete values (at least five different values, and preferably at least ten different values or more).

In an embodiment of the control method, the exhaust gas treatment system controlling step S2 includes:

521) controlling injection of DEF in the exhaust passage; and/or

522) controlling a heating of the DEF tank.

Advantageously, when step S21 is carried out, it is possible to operate the engine in a driving mode as soon as possible after start, even by cold weather. In particular, since the icing state of the DEF tank is known, it is possible to ensure at any time that a sufficient amount of DEF in the liquid phase remains available for injection in the exhaust passage of the engine.

In addition, when step S22 is carried out, it is possible to reduce energy consumption to a minimum.

In an embodiment of the control method, the DEF tank icing state determination step SI) includes

512) determining an energy amount exchanged by the DEF tank; and

513) determining the icing state based on the energy amount exchanged by the DEF tank and a previous icing state of the DEF tank.

In particular, in a variant of the above embodiment, at step S12, determining the energy amount exchanged by the DEF tank comprises:

5121) determining an energy amount exchanged by a coolant tank of the internal combustion engine; and

5122) determining the energy amount exchanged by the DEF tank based on the energy amount exchanged by the coolant tank. Furthermore, at step S121, the energy amount exchanged by the coolant tank may be estimated based on a duration of soaking time of the engine and a temperature difference of the coolant temperature between the beginning and the end of the soaking time. (The soaking time is the period between a stoppage of the engine until the next start of the engine).

In a particular implementation, the various steps of the method for identifying a cause of blockage in a sequence of images are determined by computer program instructions.

Accordingly, the invention also provides a computer program which is stored on a computer-readable storage media, and which is suitable for being performed in a computer, the program including instructions adapted to perform the steps of the method described above when it is run on the computer.

The computer program may use any programming language, and be in the form of source code, object code, or code intermediate between source code and object code, such as in a partially compiled form, or in any other desirable form.

The invention also provides a computer-readable recording medium including instructions of a computer program as mentioned above.

The recording medium may be an entity or device capable of storing the program; in particular, in a non-transitory manner. For example, the medium may comprise storage means, such as a read only memory (ROM), e.g. a compact disk (CD) ROM, or a microelectronic circuit ROM, or indeed magnetic recording means, e.g. a floppy disk or a hard disk.

Alternatively, the recording medium may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method in question.

Another object of the present invention is to provide an internal combustion engine of the type defined in introduction, whose exhaust treatment system can be controlled in an optimized manner, even when the outside temperature is below the freezing temperature of the DEF.

To meet this purpose, an internal combustion engine of the type defined in introduction is proposed.

Specifically, this internal combustion engine has an electronic control unit configured to:

SI) determine an icing state of the DEF tank; and S2) control the exhaust gas treatment system based on an icing state of the DEF tank.

In an embodiment, the electronic control unit is further configured:

S21) to control injection of DEF in the exhaust passage; and/or

S22) to control a heater provided to heat the DEF tank.

In an embodiment, the electronic control unit is further configured, in order to determine the DEF tank icing state:

512) to determine an energy amount exchanged by the DEF tank; and

513) to determine the icing state based on the energy amount exchanged by the DEF tank and a previous icing state of the DEF tank.

In particular, in a variant of the above embodiment, the electronic control unit is further configured, in order to determine the energy amount exchanged by the DEF tank:

5121) to determine an energy amount exchanged by a coolant tank of the internal combustion engine;

5122) to determine the energy amount exchanged by the DEF tank based on the energy amount exchanged by the coolant tank.

Furthermore, the electronic control unit may further be configured to determine the energy amount exchanged by the coolant tank based on a duration of soaking time of the engine and a temperature difference of the coolant temperature between the beginning and the end of the soaking time.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood and its numerous other objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing wherein like reference numerals refer to like elements in the several figures and in which :

Fig.l is a schematic figure showing an internal combustion according to the present disclosure;

Fig.2 is a flowchart showing the steps of a method in an embodiment of the present disclosure.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 schematically illustrates an internal combustion engine 10, as an exemplary embodiment of the present disclosure. Engine 10 is representative of a diesel engine which propels a motor vehicle such as a commercial vocational vehicle like a bus or delivery truck.

The internal combustion engine 10 (hereinafter, the 'engine 10') is provided with an exhaust gas treatment system 20 and an electronic control unit 100.

The exhaust gas treatment system 20 comprises an exhaust gas passage 22, an SCR catalyst 26, interposed on the exhaust gas passage 22, and a diesel exhaust fluid DEF injection system 30. The exhaust gas treatment system 20 may further comprise other not-represented components (oxidation catalyst, etc.).

The selective catalytic reduction (SCR) catalyst 26 is configured to reduce nitrogen oxides (NOx) in the exhaust gas flowing through exhaust passage 22.

The DEF injection system 30 comprises a DEF tank 40 and is configured to inject DEF in the exhaust gas passage upstream the SCR catalyst 26. In this purpose, the DEF injection system 30 comprises a DEF injector 32 arranged on the exhaust passage 22, and configured to inject DEF into the exhaust passage 22 to form ammonia (NH3), a duct 34 through which DEF can flow from the DEF tank 40 to the DEF injector 32.

The flow of DEF in duct 34 is controlled by a regulator valve 36, which itself is controlled by the electronic unit 100.

The amount of DEF in DEF tank 40 is metered by a meter 38.

The DEF tank 40 further comprises a heater 42. The heater 42, controlled by the electronic control unit 100, is used to heat the DEF contained in the DEF tank 40 and melt it if the outside temperature is below the freezing temperature of the DEF.

The engine further comprises a coolant tank 15, which contains a coolant fluid used to reduce the inner temperature of the engine during operation. The temperature of the coolant tank is measured by a temperature sensor 50.

The engine further comprises a clock 52 which outputs time, as an example of a system to provide time information to the electronic control unit 100.

A method for controlling the engine 10 will now be presented in relation with Fig.2.

The method comprises two steps SI and S2. During the soaking time of the engine, in step SI the icing state 1% of the DEF tank 40 is determined. Step SI is carried out iteratively so as to calculate at each time step the value of the icing state of the DEF tank.

Iterations are triggered at regular time steps by the electronic control unit 100, on the basis of time measurements by clock 52.

Then, when the engine is started, step S2 is carried out: The exhaust gas treatment system 20 is controlled based on the icing state 1% determined at step SI. SI - Icing state 1% determination

The icing state 1% of the DEF tank is determined in two steps.

In preamble, the amount of change of the temperature of the coolant since the previous time step is determined (step Sll).

Then at step S12, the energy amount E3 exchanged by DEF tank 40 is determined.

This determination comprises two sub-steps:

In a first sub-step S121, the energy amount El exchanged by coolant tank 15 is determined. The energy amount El is calculated using a mathematical model describing the thermal exchanges of the coolant tank. With such a model, the energy amount exchanged by the coolant tank can be determined as a function of the temperature change of the coolant tank.

Accordingly in this sub-step, the energy amount El exchanged by the coolant tank 15 is estimated based on a duration of the time step (during soaking) and a temperature difference of the coolant temperature between the beginning and the end of the time step.

In a second sub-step S122, the energy amount E3 exchanged by the DEF tank since the previous time step is determined based on the energy amount El.

Again, this determination comprises two operations:

S1221) the energy amount E2 exchanged by the vehicle since the previous time step is calculated based on the energy amount El. The energy amount E2 is calculated using a mathematical model describing the thermal exchanges of the vehicle and those of the coolant tank. S1222) the energy amount E3 is then calculated based on the energy amount E2. The energy amount E3 is calculated using a mathematical model describing the thermal exchanges of the vehicle and those of the DEF tank.

Then at step S13, the icing state 1% is determined, on the basis of the energy amount E3 and of the icing state 1% of the DEF tank 40 at the previous time step. This calculation takes into account the thermal capacity per mass unit of the DEF.

S2 - Exhaust aas treatment system control

The exhaust gas treatment system controlling step S2 includes two steps, which are carried out independently from each other.

In a step S21, the injection of DEF in the exhaust passage 22 is controlled by the electronic control unit 100. This control is determined based on the icing state of DEF tank 40, in two sub-steps:

In a first sub-step S211, the amount of DEF in the liquid state in DEF tank 40 is determined. It is equal to the total amount of DEF in the DEF tank multiplied by (1-1%), where 1% is the icing state.

If the amount of DEF in the liquid state exceeds a predetermined threshold, it is determined that, as far as DEF injection is concerned, the engine can be operated in 'drive mode', in which the exhaust emissions are reduced. This information (or 'flag') is taken into account by the electronic control unit 100 to control the engine.

In a second sub-step S212, injection of DEF in the exhaust passage 22 is controlled by electronic control unit 100. The amount to inject is calculated in function of the available amount of DEF in the liquid state in the DEF tank.

For instance, in this exemplary embodiment:

• if the amount of DEF in the liquid state in the DEF tank is below a first predetermined threshold, no DEF is injected;

• if the amount of DEF in the liquid state in the DEF tank is above the first predetermined threshold but below a second predetermined threshold which is higher than the first predetermined threshold, an amount of DEF which is lower than a predetermined normal injection amount is injected; and

• if the amount of DEF in the liquid state in the DEF tank is above the second predetermined threshold, the normal injection amount of DEF is injected. In addition, at step S22, the heater 42 of DEF tank 40 is controlled based on the icing state 1% of DEF tank 40. Several options are available. For instance, in order to save as much energy as possible, the heater 42 may be operated each time the amount of DEF in the liquid state is below the above- mentioned first predetermined threshold - but only during such periods. In this case, step S22 is carried out after step S211 (arrow in dotted line on Fig.2).

The heater 42 might otherwise be operated as soon as the icing state 1% exceeds a predetermined value, regardless of the actual quantity of DEF in the liquid state.

The electronic unit 100 has the hardware architecture of a computer. It comprises a microprocessor 102, a random access memory (RAM) 104 and a read only memory (ROM) 106. These hardware elements are optionally shared with other units of the engine 10.

The read-only memory 106 of the electronic control unit 100 constitutes a recording medium in accordance with the invention, readable by the microprocessor 102 and on which is recorded a computer program according to the disclosure, comprising instructions for the execution of the steps of a control method according to the present disclosure, now described with reference to FIG. 2.