Abstract:
An exhaust gas treatment system includes: confirming that an engine stops operation; sensing present pressure difference between front and rear sides of an EGR value; setting learning value by performing large offset learning, if the present pressure difference exceeds an absolute value of a first lower or upper values; setting learning value by performing step learning, if the present pressure difference exists between first and second lower values that is larger than the first lower value or the present pressure difference a between first and second upper values that is smaller than the first upper value; and setting the present pressure difference value as a learning value, if the present pressure difference exists between the second lower and second upper values. The exhaust gas treatment method accurately learns the pressure difference of the EGR system to improve the quality of the exhaust gas and securely control the EGR system.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority of Korean Patent Application Number 10-2011-0127971 filed Dec. 1, 2011, the entire contents of which application is incorporated herein for all purposes by this reference. 
       BACKGROUND OF INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to an exhaust gas treatment method that improves quality of exhaust gas by accurately learning a pressure difference of the EGR system while a negative pressure is formed in an exhaust line. 
         [0004]    2. Description of Related Art 
         [0005]    Generally, after a vehicle stops its operation, a front/rear pressure of an EGR valve is learned, and the pressure difference learning can be performed in a vacuum condition in which a negative pressure is formed in at least one side of an exhaust line. 
         [0006]    The negative pressure is a value that is generated while exhaust gas is sucked by a separate device in a test site so as to measure the exhaust gas or exhaust the exhaust gas to the outside, and in a case that the negative pressure is −10 hpa, the pressure difference of the EGR system is increased as much as +10 hpa. 
         [0007]    Particularly, because an EGR line is diverged from a downstream side of a DPF in an LP-EGR system, when a negative pressure is formed in an exhaust line, a fluctuation width of the pressure difference can be increased, and when this fluctuated value is learned, the control system can be abnormal. 
         [0008]    Further, because the pressure difference of the EGR system is differently measured, nitrogen oxide and particulate matter that are sensitively regulated can be excessively increased. 
         [0009]    The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
       BRIEF SUMMARY 
       [0010]    Various aspects of the present invention provide for an exhaust gas treatment system including confirming that an engine stops its operation; sensing a present pressure difference between a front side and a rear side of an EGR value of an EGR line by using a pressure difference sensor; setting a learning value by performing large offset learning, if the present pressure difference exceeds an absolute value of a first lower value or a first upper value; setting a learning value by performing step learning, if the present pressure difference exists between the first lower value and a second lower value that is larger than the first lower value or the present pressure difference a between the first upper value and a second upper value that is smaller than the first upper value; and setting the present pressure difference value as a learning value, if the present pressure difference exists between the second lower value and the second upper value. 
         [0011]    The large offset learning may include storing the present pressure difference value detected by the pressure difference sensor by as much as a predetermined frequency at a predetermined interval, and setting an averaged value except a maximum value and a minimum value from the stored values as a learning value. 
         [0012]    While storing the present pressure difference value detected by the pressure difference sensor by as much as a predetermined frequency, if the predetermined frequency is not stored, a former pressure difference value may be used to be a learning value. 
         [0013]    The step of learning may include subtracting a first predetermined value from a former learning value to set a learning value. 
         [0014]    The first predetermined value that is subtracted may correspond to a negative pressure that is formed in an exhaust line. 
         [0015]    The first predetermined value may be a value that exists between the second lower value and the second upper value. 
         [0016]    Various aspects of the present invention provide for an exhaust gas treatment method that accurately learns the pressure difference of the EGR system to improve the quality of the exhaust gas and securely control the EGR system. 
         [0017]    The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a schematic diagram of an exemplary exhaust gas treatment device according to the present invention. 
           [0019]      FIG. 2  is a flowchart showing an exemplary exhaust gas treatment method according to the present invention. 
           [0020]      FIG. 3  is a graph showing an exemplary exhaust gas treatment method according to the present invention. 
           [0021]      FIG. 4  is a flowchart showing large offset learning logic in an exemplary exhaust gas treatment method according to the present invention. 
           [0022]      FIG. 5  is a table showing an example of large offset learning logic in an exemplary exhaust gas treatment method according to the present invention. 
           [0023]      FIG. 6  is a flowchart showing step learning logic in an exemplary exhaust gas treatment method according to the present invention. 
           [0024]      FIG. 7  is a graph showing an example of step learning logic in an exemplary exhaust gas treatment method according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0026]      FIG. 1  is a schematic diagram of an exhaust gas treatment device according to various embodiments of the present invention. 
         [0027]    Referring to  FIG. 1 , an exhaust gas treatment device includes an EGR valve  110 , a pressure difference sensor  120 , an engine  130 , and a control portion  100 . The engine  130  exhausts exhaust gas to the outside through an exhaust line, and an EGR line, which recirculates exhaust gas of a downstream side of the diesel particulate filter (DPF) to an intake line, is formed in the exhaust line. 
         [0028]    The EGR valve  110  is disposed on the EGR line to control the flow rate of the EGR gas, the control portion  100  learns a front and rear pressure difference of the EGR valve  110  to control the EGR valve  110 , and the learned value is used to control the engine  130 . 
         [0029]    The pressure difference sensor  120  can be disposed to detect the front and rear pressure difference of the EGR valve  110 . 
         [0030]    An EGR system according to various embodiments of the present invention is a low pressure type (LP-EGR system) where the exhaust gas is diverged from a downstream side of the diesel particulate filter to be transferred to an intake line. 
         [0031]    Further, a high pressure type (HP-EGR system) recirculates the exhaust gas from an upstream side of the diesel particulate filter to an intake line. The HP-EGR system can be applied in various embodiments of the present invention instead of the LP-EGR system. 
         [0032]    The control portion  100  detects a condition of the engine, and if it is determined that the engine stops operation, the front/rear pressure difference of the EGR valve  110  is learned by the control portion through the pressure difference sensor  120  in various embodiments of the present invention. 
         [0033]    Particularly, when a vacuum line is connected to the exhaust line, the front/rear pressure difference of the EGR valve  110  is sharply fluctuated and a control factor such as nitrogen oxide is also varied, and therefore it is necessary to accurately detect the front/rear pressure difference of the EGR valve  110 . 
         [0034]      FIG. 2  is a flowchart showing an exhaust gas treatment method according to various embodiments of the present invention. 
         [0035]    Referring to  FIG. 2 , control starts in S 200 , and it is confirmed that the engine  130  is stopped in S 210 . 
         [0036]    It is determined whether a pressure difference value of the pressure difference sensor  120  exists between a first lower value C 1  and a first upper value C 4  in S 220 , and if it is determined that the present pressure difference value (ΔP) exceeds a range of the first lower value C 1  and the first upper value C 4 , S 250  is performed. 
         [0037]    Further, if the present pressure difference value (ΔP) is included in the range of the first lower value C 1  and the first upper value C 4 , S 230  is performed. If the present pressure difference value (ΔP) exists between the second lower value C 2  that is larger than the first lower value C 1  and the second upper value C 3  that is smaller than the first upper value C 4  in S 230 , S 240  is performed. 
         [0038]    The size relation is “the first lower value C 1 &gt;the second lower value C 2  &gt;the second upper value C 3 &gt;the first upper value C 4 ”. 
         [0039]    The present pressure difference value (ΔP) that is detected in the pressure difference sensor  120  is set as a learning value in S 240 . For example, when it is assumed that C 1 =−5, C 2 =−3, C 3 =3, and C 4 =5, the present pressure difference value (ΔP) that is detected by the pressure difference sensor  120  is −1, a learning value is set as −1. The learning value is used as a new control factor in the control portion  100 . 
         [0040]      FIG. 3  is a graph showing an exhaust gas treatment method according to various embodiments of the present invention. 
         [0041]    Referring to  FIG. 3 , C 1  (the first lower value), C 2  (the second lower value), C 3  (the second upper value), and C 4  (the first upper value) are set as reference values, and if the present pressure difference value (ΔP) exists between C 2  (the second lower value) and C 3  (the second upper value), the value is set as a learning value. 
         [0042]    Further, if the present pressure difference value (ΔP) is included between C 1  (the first lower value) and C 2  (the second lower value) or is included between C 3  (the second upper value) and C 4  (the first upper value), step learning is performed, and if the value (ΔP) exceeds C 1  (the first lower value) and C 4  (the first upper value), a large offset is performed. 
         [0043]    The present pressure difference value (ΔP) accurately coincides with C 1  (the first lower value), C 2  (the second lower value), C 3  (the second upper value), or C 4  (the first upper value) in various embodiments of the present invention, for example, if the present pressure difference value (ΔP) is C 1  (the first lower value), large offset learning or step learning can be performed according to a design specification. 
         [0044]    The boundary values such as C 1 , C 2 , C 3 , and C 4  can be variably applied in various embodiments of the present invention. 
         [0045]      FIG. 4  is a flowchart showing large offset learning logic in an exhaust gas treatment method according to various embodiments of the present invention. 
         [0046]    Referring to  FIG. 4 , it is determined whether the present pressure difference value (ΔP) exists between the first lower value C 1  and the first upper value C 4  in S 400 , and if the value exceeds the range, S 410  is performed. 
         [0047]    The present pressure difference value (ΔP) is stored in S 410 , the value is stored N times at a predetermined interval in S 420 , a maximum value and a minimum value among values that are stored N times are excluded in S 430 , and the average value of the values that are not excluded is calculated. This average value is set as the learning value. 
         [0048]    In S 420 , if the stored frequency does not reach N, a prior learning value of the pressure difference sensor is reused. 
         [0049]      FIG. 5  is a table showing an example of large offset learning logic in an exhaust gas treatment method according to various embodiments of the present invention. 
         [0050]    Referring to  FIG. 5 , a present pressure difference value is stored six times, a maximum value of 3.83 and a minimum value of 3.48 are erased, an average value of the values remaining is 3.65, and the 3.65 is set as a learning value of a final pressure difference offset. 
         [0051]      FIG. 6  is a flowchart showing step learning logic in an exhaust gas treatment method according to various embodiments of the present invention. 
         [0052]    Referring to  FIG. 6 , if the present pressure difference value (ΔP) exists within the first lower value C 1  and the first upper value C 4  in S 600  and the present pressure difference value (ΔP) does not exist between the second lower value C 2  and the second upper value C 3  in S 610 , S 620  is performed. 
         [0053]    In S 620 , a first predetermined value (C_Step) is subtracted from a learning value of a prior pressure difference sensor  120  value and a new learning value is set. It is desirable that the first predetermined value (C_Step) is included between the second lower value C 2  and the second upper value C 3 . Further, the first predetermined value (C_Step) can correspond to a value of a negative pressure that is formed in the exhaust line. 
         [0054]      FIG. 7  is a graph showing an example of step learning logic in an exhaust gas treatment method according to various embodiments of the present invention. 
         [0055]    Referring to  FIG. 7 , when the first lower value C 1  is −5, the second lower value C 2  is −2, the second upper value C 3  is 2, the first upper value C 4  is 5 hpa, a prior final learning value is −2, and a present offset learning value is −3, a present value of the pressure difference sensor is −4. Further, the first predetermined value is 1 hpa. 
         [0056]    That is, when a present pressure difference value of the pressure difference sensor  120  is −4, if step learning is performed and the first predetermined value of 1 is subtracted from a prior final learning value of −2 according to step learning flow, the present final learning value is −3 hpa. 
         [0057]    For convenience in explanation and accurate definition in the appended claims, the terms upper or lower, front or rear, inside or outside, and etc. are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
         [0058]    The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.