Abstract:
A system for preventing the accumulation of unburned hydrocarbons in a line of exhaust gas after-treatment system of an internal combustion engine comprising at least one devise for the reduction of pollutant emissions, wherein the exhaust gas after treatment system is devoid of any pre-catalyst and a procedure is envisioned for the continuous estimation of a mass of unburned hydrocarbons stored at least in the device for the reduction of pollutant emissions, so as to activate a strategy for accelerating the heating of the exhaust line, when the mass of unburned hydrocarbons exceeds a predefined threshold.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to Italian Patent Application No. M12014A000291 filed Feb. 26, 2014, the entirety of the disclosures of which are expressly incorporated herein by reference. 
       STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
       [0002]    Not Applicable. 
       SCOPE OF THE INVENTION 
       [0003]    The present invention relates to the field of purification systems of exhaust gases of an internal combustion engine and more precisely to a system for preventing the accumulation of unburned hydrocarbons in a line of exhaust gas after-treatment system. 
       BACKGROUND ART 
       [0004]    The after treatment systems of exhaust gases, generally referred to with the acronym ATS, are generally provided with at least one catalyst which provides for the conversion of the unburned hydrocarbons (CnHm), nitrogen oxides (NO) and carbon monoxide (CO) into carbon dioxide (CO2), water (H2O) and nitrogen (N2). 
         [0005]    It is known that a catalyst is fully activated, i.e. becomes operational, upon achieving at least 250° C. But already at 200° C., it can convert at least the unburned hydrocarbons. 
         [0006]    Systems/strategies are known to accelerate the heating step of the exhaust line of an internal combustion engine. 
         [0007]    Generally, they are based on the choking of the exhaust line, for example through a flap or by reducing the outflow section of a variable-geometry turbine arranged on the exhaust line. Other systems/strategies to accelerate the heating step of the exhaust line consist in post-injection of fuel. Further systems/strategies comprise the activation of suitable electric heater. 
         [0008]    Said systems/strategies to accelerate the heating step of the exhaust line ATS are well known to the skilled person in the art, thus, it is not needed to offer further details. 
         [0009]    Therefore, said systems/strategies offer a further contribution in heating up the ATS, with respect to the normal contribution of the internal combustion engine, helping the latter for this aim. 
         [0010]    The control processes of these systems, according to different control techniques, activate after a predefined period of time since the ignition of the internal combustion engine, for example after verifying a too slow dynamic heating of the ATS, or they can be deactivated by other processes when the latter determine that such systems are not able to lead to the complete activation of the catalyst. 
         [0011]    During the heating step, the unburned hydrocarbons, for simplicity referred to as HC, tend to accumulate in the catalyst. 
         [0012]    When the catalyst reaches the activation temperature, an excessive accumulation of HC could damage the catalyst due to the achievement of temperatures above those admissible for the device itself. 
         [0013]    The prior art, in order to avoid damage to the catalyst, provides for the implementation of the so-called pre-catalysts, i.e. additional catalysts, having a very small volume compared to the main catalyst, which are accommodated very close to the exhaust manifold of the internal combustion engine, so as to achieve as soon as possible such an activation temperature as to burn the unburned hydrocarbons produced by the internal combustion engine before they reach the main catalyst or any device for the reduction of pollutant emissions defining the ATS. 
         [0014]    The implementation of pre-catalysts requires an additional cost for manufacturers of vehicles and machinery, in addition, they must be designed so as not to interfere with other devices, such as the main catalyst and any particulate filters. 
       SUMMARY OF THE INVENTION 
       [0015]    The object of the present invention is to overcome all the above drawbacks and provide a system for preventing the accumulation of unburned hydrocarbons in a line of exhaust gas after treatment system devoid of pre-catalysts. 
         [0016]    The idea at the basis of the present invention is to prevent the implementation of any pre-catalyst, estimating the accumulation of unburned hydrocarbons in at least one point/component of the line of exhaust gas after treatment system, and to activate systems/strategies of heating of the exhaust line also on the basis of the accumulation of the estimated unburned hydrocarbons. 
         [0017]    This implies that the processes for accelerating the heating of the exhaust line are controlled differently compared to the prior art. 
         [0018]    In particular, the process of estimating the accumulation of unburned hydrocarbons in the line of exhaust gas after treatment system (ATS) takes priority over any further activation or deactivation process, on the control of the process for accelerating the heating of the exhaust gas after treatment line. Therefore, it may happen that the process for accelerating the ATS heating is activated earlier compared to prior art, or that it remains active even when other processes might control the deactivation thereof. 
         [0019]    The object of the present invention is a system for preventing the accumulation of unburned hydrocarbons in a device for the reduction of pollutant emissions defining a line of exhaust gas after treatment system of an internal combustion engine. 
         [0020]    A device for the reduction of pollutant emissions may refer to at least one of the following per se known devices: DOC, NSC, DPF, SCR. 
         [0021]    The claims are an integral part of the present description. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0022]    Further features and advantages of the present invention will be clear from the following detailed description of an exemplary embodiment of the same (and variants thereof) and from the accompanying drawings given by way of a non-limiting example, in which: 
           [0023]      FIG. 1  shows a logical control diagram according to the present invention; 
           [0024]      FIG. 2  shows an exemplary implementation of the present invention through a flowchart; 
           [0025]      FIG. 3  schematically shows an internal combustion engine operatively connected to an exhaust gas after treatment system to which the present invention is applied. 
       
    
    
       [0026]    The same reference numerals and letters in the figures identify the same elements or components. 
         [0027]    In the context of the present description, the terms “first”, “second”, etc. do not indicate any reciprocal relationship nor they are intended to be limiting. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0028]      FIG. 1  shows a logical control diagram of the activation of a process for accelerating (WATSP) the heating of the after treatment system (ATS). 
         [0029]    The abbreviation WATSP is the acronym of the expression “WarmUP ATS Process”, i.e. a process/system for accelerating the heating of the ATS, which as described above can be achieved in different ways, including choking of the exhaust line and/or the fuel post-injection and/or the activation of a suitable heater arranged inside or around a portion of the ATS piping. 
         [0030]    Other processes S 1 , S 2 , S 3  may intervene to control the WATSP according to specific/predefined control strategies, causing the activation or deactivation. 
         [0031]    According to the present invention, a process S estimates the amount of HC accumulated in at least one point in the exhaust line ATS and when such an estimate exceeds a first predefined threshold, the activation S-ON of the WATSP is controlled irrespective of any ether ongoing process. 
         [0032]    Such a process S takes priority over all the others S 1 , S 2 , S 3  . . . and therefore this is graphically shown by an arrow much thicker than the others. 
         [0033]    Thereafter, when the estimated HC are less than a second predefined threshold, the WATSP returns under the control of the other processes S 1 , S 2 , S 3 . Therefore, the WATSP remains active if one of them deems that the WATSP must be active, or if no process forces the deactivation thereof. 
         [0034]    Therefore, the HC estimation process does not have the power to deactivate the WATSP (process for accelerating the ATS heating), but just to activate it. 
         [0035]    Therefore, irrespective of the hierarchy of the known processes that can determine the activation or deactivation of the WATSP, the present estimation process S is virtually parallel to such a hierarchy. 
         [0036]      FIG. 2  shows an example of a control flowchart according to the present invention. 
         [0037]    Step  1 : ignition of internal combustion engine E; 
         [0038]    Step  2 : acquisition of a residual value R of HC stored in the ATS, 
         [0039]    Step  3 : estimate of the mass of HC produced P and of the mass of HC converted C, 
         [0040]    Step  4 : calculation of the mass I of HC stored in the exhaust line (at least one point of the exhaust line): I=R+P−C; 
         [0041]    Step  5 : verification of whether I is greater than a first threshold T1, 
         [0042]    Step  6 : if so, WATSP activation, otherwise 
         [0043]    Step  9 : verification of whether I is smaller than a second threshold T1[?] 
         [0044]    Step  10 : if so, WATSP deactivation and go to step  13 ; 
         [0045]    otherwise, go to step  13 ; 
         [0046]    after activating the WATSP (step  6 ) 
         [0047]    Step  7 : verification of whether I is greater than a third threshold T3, 
         [0048]    Step  8 : if so, activation of a protection procedure on the internal combustion engine 
         [0049]    otherwise 
         [0050]    Step  11 : verification of whether I is smaller than a fourth T4 lower than T3 and higher than T2[?] 
         [0051]    Step  12 : if so, deactivation of the protection procedure on the internal combustion engine and then go to step  13 ; 
         [0052]    Step  13 : verification of whether the internal combustion engine is switched off, 
         [0053]    Step  14 : if so, assigning Ito R (I=R) and the end of the control at step  15 , otherwise continue from step  3 , i.e. from the estimate of the mass of HC produced P and of the mass of HC converted C. 
         [0054]    From the example of flowchart in  FIG. 2  it is clear that, when it is not possible to dispose of the HC mass produced by the internal combustion engine, a condition is reached where the HC mass stored in the exhaust line exceeds a second threshold T2; in that case, measures are taken to thereafter prevent reaching the activation temperature of the catalyst CAT, as this could lead to damage to the catalyst itself and/or to the entire vehicle. 
         [0055]    For example, such measures may consist in limiting the torque delivered by the engine and the consequent production of heat, which would make the ATS heat up and probably catch fire. 
         [0056]    Should the HC mass I exceed such a second threshold T2, according to the present invention, an error would be permanently stored in the engine control unit, ECU, which controls the lighting of an indicator light indicating a fault that requires the vehicle to be brought to a workshop. 
         [0057]    As regards the estimate of the HC produced by the internal combustion engine, it is possible to rely on heuristic maps, i.e. obtained at the bench on the basis of RPM, mass of fuel injected, intake air mass and preferably also ambient temperature. All these parameters are generally available to the control unit ECU of internal combustion engines using appropriate sensors, therefore the implementation of such maps into a control unit ECU is within the skills of the man skilled in the art. 
         [0058]    As regards the estimate of the HC converted by the exhaust line, it varies from component to component: catalyst DOC, NSC (NOx Storage Catalyst), DPF, SCR, and depending essentially on the conformation of the single component that defines the ATS and on the temperature thereof. 
         [0059]    Also the temperature of various points of the ATS is available to the ECU through appropriate sensors, therefore also the implementation of the estimate of the HC converted is within the skills of the man skilled in the art. 
         [0060]    Mathematical models or bench tests may be adopted to estimate the conversion process of each component defining the ATS as a function of its temperature. 
         [0061]    In view of the fact that the various components that define the ATS may have different behaviors in terms of accumulation or conversion of HC, the present method can be implemented in two different ways, i.e. by estimating the HC stored in the most problematic component, i.e. the component that tends to more easily store HC, which typically is the catalyst (DOC or SCR) and/or the particulate filter, or by estimating the individual accumulations of HC in the single components/devices that define the ATS. 
         [0062]    Therefore, the present system may be implemented by estimating a storage of HC at least in a device for the reduction of pollutant emissions that defines the ATS. 
         [0063]    The method may be advantageously implemented by modifying/adapting the processing unit ECU of the internal combustion engine. 
         [0064]      FIG. 3  schematically shows an internal combustion engine E controlled by a processing unit ECU, which among the various engine parameters described above also receives a signal related to at least the catalyst temperature. 
         [0065]    According to a preferred implementation of the present invention, the internal combustion engine is a diesel cycle and the above catalyst is a DOC, per se known. 
         [0066]    The present invention may be advantageously implemented by a computer program which comprises coding means for implementing one or more steps of the method, when this program is run on a computer. 
         [0067]    Therefore, it is understood that the scope of protection extends to said computer program and moreover to computer-readable means which comprise a recorded message, said computer-readable means comprising program coding means for implementing one or more steps of the method when said program is run on a computer. 
         [0068]    Embodiment variants of the non limiting example described are possible without departing from the scope of protection of the present invention, comprising all the equivalent embodiments for a man skilled in the art. 
         [0069]    From the above description, the man skilled in the art is able to implement the object of the invention without introducing any further construction details. The elements and the features shown in the different preferred embodiments may be combined without departing from the scope of protection of the present application. What described in the description of the prior art, unless specifically excluded in the detailed description, must be considered in combination with the features of the present invention, forming an integral part of the present invention.