Abstract:
A system and method for desulfurizing an oxidation catalyst enhances fuel economy and reduces noxious exhaust gas emission as a consequence of increasing desulfurization period of the oxidation catalyst or shortening desulfurization time by reflecting desulfurization history consisting of natural desulfurization occurrence. The method may include detecting an inlet temperature of the oxidation catalyst, estimating natural desulfurization according to the inlet temperature of the oxidation catalyst, and resetting desulfurization time or desulfurization period by reflecting the estimated natural desulfurization.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2010-0108881 filed on Nov. 3, 2010, 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 a system for desulfurizing an oxidation catalyst and a method thereof. More particularly, the present invention relates to a system for desulfurizing an oxidation catalyst and a method thereof which reduce fuel consumption and purify noxious exhaust gas as a consequence of increasing desulfurization period of the oxidation catalyst or shortening desulfurization time by reflecting desulfurization history considering natural desulfurization occurrence. 
         [0004]    2. Description of Related Art 
         [0005]    An exhaust gas generated from an internal combustion engine contains harmful substances such as carbon monoxide (CO), hydrocarbon (HC), and soluble organic fraction (SOF), and an oxidation catalyst is generally used for cleaning these harmful substances. 
         [0006]    The oxidation catalyst purifies CO and HC into CO 2  and H 2 O by using a catalyst of platinum family coated on a ceramic carrier. 
         [0007]    The oxidation catalyst has two degradation mechanisms. One of them is non-reversible degradation wherein the catalyst is exposed to high temperature and effective surface area is reduced, and the other of them is reversible sulfur-poisoning wherein reaction sites are contaminated and reduced by sulfur. 
         [0008]    The reversible sulfur-poisoning means that activity of the oxidation catalyst is deteriorated by the sulfur contained in fuel or engine oil. Since the sulfur-poisoning is reversible reaction, the deteriorated activity of the oxidation catalyst can be restored. 
         [0009]    It is called “desulfurization” that the activity of the oxidation catalyst is restored from the sulfur-poisoning. The desulfurization is generally performed by exposing the oxidation catalyst to high temperature (e.g., higher than 450° C.). 
         [0010]    That is, the desulfurization of the oxidation catalyst is performed by exposing the oxidation catalyst to the high temperature (e.g., higher than 450° C.) when desulfurization period according to travel distance or driving time is reached, or oxidizing performance of the oxidation catalyst falls below a predetermined level. 
         [0011]    However, in order to make the oxidation catalyst exposed to high temperature environment in desulfurization, fuel must be post-injected or be additionally injected. Therefore, additional fuel may be used and fuel economy may be worsen. 
         [0012]    As shown in  FIG. 9 , the desulfurization of the oxidation catalyst is repetitively performed by means of post-injection at every predetermined travel distance (e.g., 15,000 km) for every predetermined time (e.g., 5 min.). 
         [0013]    If the desulfurization of the oxidation catalyst is performed at every predetermined desulfurization period, the activity of the oxidation catalyst can be restored but additional fuel consumption is necessary to make the high temperature environment. Thereby fuel economy may be deteriorated, noxious exhaust gas may increase, and oil dilution may occur. 
         [0014]    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. 
       SUMMARY OF INVENTION 
       [0015]    Various aspects of the present invention provide for a system for desulfurizing an oxidation catalyst and a method thereof having advantages of enhancing fuel consumption, reducing noxious exhaust gas, and minimizing non-reversible degradation of the oxidation catalyst as a consequence of increasing desulfurization period of the oxidation catalyst or shortening desulfurization time by reflecting desulfurization history considering natural desulfurization occurrence. 
         [0016]    A system for desulfurizing an oxidation catalyst according to various aspects of the present invention may include an engine, an oxidation catalyst purifying harmful substances contained in exhaust gas, a temperature detector detecting inlet temperature of the oxidation catalyst, and a control portion integrating a time or a distance where natural desulfurization occurs based on the inlet temperature of the oxidation catalyst, and performing desulfurization of the oxidation catalyst by reflecting integrated natural desulfurization occurrence time or integrated natural desulfurization occurrence distance on a predetermined desulfurization time or a predetermined desulfurization period. 
         [0017]    The control portion may calculate integrated time or integrated distance where the inlet temperature of the oxidation catalyst is higher than a predetermined desulfurization temperature as the natural desulfurization occurrence time or the natural desulfurization occurrence distance. 
         [0018]    The control portion may be adapted to reduce desulfurization time by subtracting a value corresponding to the integrated natural desulfurization occurrence time from the predetermined desulfurization time. 
         [0019]    The control portion may be adapted to increase desulfurization period by reflecting a value corresponding to the integrated natural desulfurization occurrence time on the predetermined desulfurization period. 
         [0020]    The control portion may maintain the predetermined desulfurization period in a case of reducing the desulfurization time. 
         [0021]    The control portion may maintain the predetermined desulfurization time in a case of increasing the desulfurization period. 
         [0022]    The control portion may reflect the integrated natural desulfurization occurrence time of the oxidation catalyst simultaneously on the desulfurization time and the desulfurization period. 
         [0023]    A system for desulfurizing an oxidation catalyst according to other aspects of the present invention may include an oxidation catalyst purifying harmful substances contained in exhaust gas, a temperature detector detecting inlet temperature of the oxidation catalyst, and a control portion calculating desulfurization efficiency according to the inlet temperature of the oxidation catalyst, estimating natural desulfurization degree of the oxidation catalyst by integrating the desulfurization efficiency according to the inlet temperature of the oxidation catalyst to time or distance, and performing desulfurization of the oxidation catalyst by reflecting the estimated natural desulfurization degree on a predetermined desulfurization time or a predetermined desulfurization period. 
         [0024]    The control portion may be adapted to reduce desulfurization time by subtracting a value corresponding to the estimated natural desulfurization degree from the predetermined desulfurization time. 
         [0025]    The control portion may be adapted to increase desulfurization period by adding a value corresponding to the estimated natural desulfurization degree to the predetermined desulfurization period. 
         [0026]    The control portion may maintain the predetermined desulfurization period in a case of reducing the desulfurization time. 
         [0027]    The control portion may maintain the predetermined desulfurization time in a case of increasing the desulfurization period. 
         [0028]    The control portion may reflect the estimated natural desulfurization degree simultaneously on the desulfurization time and the desulfurization period. 
         [0029]    A method for desulfurizing an oxidation catalyst according to other aspects of the present invention may include integrating a time during which an inlet temperature of the oxidation catalyst is higher than a predetermined desulfurization temperature, resetting, in a case that a predetermined desulfurization period of the oxidation catalyst is reached, desulfurization time by reflecting an integrated time during which the inlet temperature of the oxidation catalyst is higher than a predetermined desulfurization temperature on a predetermined desulfurization time, and controlling desulfurization of the oxidation catalyst according to the reset desulfurization time. 
         [0030]    The predetermined desulfurization period may be maintained when resetting the desulfurization time. 
         [0031]    A method for desulfurizing an oxidation catalyst according to other aspects of the present invention may include integrating a time during which an inlet temperature of the oxidation catalyst is higher than a predetermined desulfurization temperature, resetting, in a case that a predetermined desulfurization period of the oxidation catalyst is reached, desulfurization period by reflecting an integrated time during which the inlet temperature of the oxidation catalyst is higher than a predetermined desulfurization temperature on a predetermined desulfurization period, and controlling desulfurization of the oxidation catalyst according to the reset predetermined desulfurization period. 
         [0032]    The predetermined desulfurization time may be maintained when resetting the desulfurization period. 
         [0033]    A method for desulfurizing an oxidation catalyst according to other aspects of the present invention may include detecting an inlet temperature of the oxidation catalyst, calculating desulfurization efficiency according to the inlet temperature of the oxidation catalyst, estimating natural desulfurization degree by integrating the desulfurization efficiency according to the inlet temperature of the oxidation catalyst to time or distance, resetting, in a case that a predetermined desulfurization period of the oxidation catalyst is reached, desulfurization time by reflecting the estimated natural desulfurization degree on a predetermined desulfurization time, and controlling desulfurization of the oxidation catalyst according to the reset desulfurization time. 
         [0034]    A method for desulfurizing an oxidation catalyst according to other aspects of the present invention may include detecting an inlet temperature of the oxidation catalyst, calculating desulfurization efficiency according to the inlet temperature of the oxidation catalyst, estimating natural desulfurization degree by integrating the desulfurization efficiency according to the inlet temperature of the oxidation catalyst to time or distance, resetting, in a case that a predetermined desulfurization period of the oxidation catalyst is reached, desulfurization period by reflecting the estimated natural desulfurization degree on a predetermined desulfurization period, and controlling desulfurization of the oxidation catalyst according to the reset desulfurization period. 
         [0035]    A method for desulfurizing an oxidation catalyst according to other aspects of the present invention may include detecting an inlet temperature of the oxidation catalyst, estimating natural desulfurization according to the inlet temperature of the oxidation catalyst, and resetting desulfurization time or desulfurization period by reflecting the estimated natural desulfurization. 
         [0036]    The natural desulfurization of the oxidation catalyst may be estimated by integrating a time during which the inlet temperature of the oxidation catalyst is higher than a predetermined desulfurization temperature. 
         [0037]    The natural desulfurization of the oxidation catalyst may be estimated by integrating desulfurization efficiency according to the inlet temperature of the oxidation catalyst to time. 
         [0038]    The predetermined desulfurization period may be maintained and the natural desulfurization may be reflected on the desulfurization time in a case that the predetermined desulfurization period of the oxidation catalyst is reached. 
         [0039]    The predetermined desulfurization time may be maintained and the natural desulfurization may be reflected on the desulfurization period in a case that the predetermined desulfurization period of the oxidation catalyst is reached. 
         [0040]    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 
         [0041]      FIG. 1  is a schematic diagram of an exemplary system for desulfurizing an oxidation catalyst according to the present invention. 
           [0042]      FIG. 2  is a flowchart of an exemplary method for desulfurizing an oxidation catalyst according to the present invention. 
           [0043]      FIG. 3  is an exemplary schematic diagram for explaining desulfurization of an oxidation catalyst according to the present invention. 
           [0044]      FIG. 4  is a flowchart of an exemplary method for desulfurizing an oxidation catalyst according to the present invention. 
           [0045]      FIG. 5  is an exemplary schematic diagram for explaining desulfurization of an oxidation catalyst according to the present invention. 
           [0046]      FIG. 6  is a flowchart of an exemplary method for desulfurizing an oxidation catalyst according to the present invention. 
           [0047]      FIG. 7  is an exemplary graph illustrating desulfurization efficiency according to a temperature of an oxidation catalyst applied in accordance with the present invention. 
           [0048]      FIG. 8  is a flowchart of an exemplary method for desulfurizing an oxidation catalyst according to the present invention. 
           [0049]      FIG. 9  illustrates desulfurization period of the oxidation catalyst applied to a conventional vehicle. 
       
    
    
     DETAILED DESCRIPTION 
       [0050]    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. 
         [0051]    Description of components that are not necessary for explaining the present invention will be omitted, and the same constituent elements are denoted by the same reference numerals in this specification. 
         [0052]    Referring to  FIG. 1 , a system for desulfurizing an oxidation catalyst according to various embodiments of the present invention includes an engine  100 , an oxidation catalyst  200 , a temperature detector  210 , and a control unit or control portion  300 . 
         [0053]    The engine  100  burns air-fuel mixture in which air and fuel are mixed according to driving demand and load condition so as to generate power, and exhausts exhaust gas generated from combustion process to the atmosphere through an exhaust pipe. 
         [0054]    The oxidation catalyst  200  purifies harmful substances such as CO, HC, and SOF contained in the exhaust gas passing through the exhaust pipe into CO 2  and H 2 O by using a catalyst of platinum family coated on a ceramic carrier. 
         [0055]    The temperature detector  210  is disposed at an upstream of the oxidation catalyst  200 , detects temperature of the exhaust gas flowing into the oxidation catalyst  200 , and transmits inlet temperature of the oxidation catalyst  200  to the control portion  300 . 
         [0056]    The control portion  300  analyzes information transmitted from the temperature detector  210  at a normal driving mode (e.g., a driving mode at which forcible desulfurization does not occur) and integrates a time or a distance where the inlet temperature of the oxidation catalyst  200  is higher than a predetermined desulfurization temperature (e.g., 450° C.). 
         [0057]    That is, the control portion  300  integrates the time or the distance where the natural desulfurization occurs at the normal driving mode. 
         [0058]    If a predetermined desulfurization period (e.g., 15,000 km) is reached, the control portion  300  subtracts a value corresponding to the integrated time or integrated distance where the natural desulfurization occurs from the predetermined desulfurization time (e.g., 5 min.) or the predetermined desulfurization distance. That is, the control portion  300  resets desulfurization time of the oxidation catalyst  200  by reducing the same corresponding to the integrated time or the integrated distance where the natural desulfurization occurs, and controls the desulfurization of the oxidation catalyst  200  according to the reset desulfurization time. 
         [0059]    For example, the desulfurization time which was set to about 5 min. at the normal driving mode is shortened to 3 min. or 4 min. by reflecting the time or the distance where the inlet temperature of the oxidation catalyst is higher than the desulfurization temperature at the normal driving mode. Accordingly, post-injecting time for desulfurization may be shortened and fuel economy may be improved. 
         [0060]    In addition, the control portion  300  analyzes the information transmitted from the temperature detector  210  at the normal driving mode and integrates the time or the distance where the inlet temperature of the oxidation catalyst  200  is higher than the predetermined desulfurization temperature (e.g., 450° C.). 
         [0061]    If the predetermined desulfurization period (e.g., 15,000 km) is reached, the control portion  300  increases desulfurization period of the oxidation catalyst  200  corresponding to the time or the distance where the inlet temperature of the oxidation catalyst  200  is higher than the predetermined desulfurization temperature (e.g., 450° C.), and controls the desulfurization of the oxidation catalyst  200  according to the reset desulfurization period. 
         [0062]    For example, the desulfurization period which was set to about 15,000 km at the normal driving mode may be increased to 17,000 km. Therefore, the desulfurization may be performed at every 17,000 km. 
         [0063]    The reset desulfurization period is variably updated according to the integrated time or the integrated distance where the oxidation catalyst  200  is exposed to the desulfurization temperature. 
         [0064]    The control portion  300  may calculate desulfurization efficiency according to the inlet temperature of the oxidation catalyst  200  based on the inlet temperature of the oxidation catalyst  200  detected by the temperature detector  210  at the normal driving mode, and may calculate natural desulfurization degree by integrating the desulfurization efficiency according to the inlet temperature of the oxidation catalyst  20  to time or distance. Therefore, the control portion  300  can estimate actual sulfur-poisoning of the oxidation catalyst  200 . 
         [0065]    If the predetermined desulfurization period (e.g., 15,000 km) is reached, the control portion  300  resets the predetermined desulfurization time (e.g., 5 min.) by reducing it according to the actual sulfur-poisoning of the oxidation catalyst  200 , and controls the desulfurization of the oxidation catalyst  200  according to the reset desulfurization time. 
         [0066]    Therefore, post-injecting time for increasing exhaust gas temperature can be shortened, and accordingly, fuel economy may be enhanced and noxious exhaust gas emission may be reduced. 
         [0067]    In addition, the control portion  300  may calculate the desulfurization efficiency according to the inlet temperature of the oxidation catalyst  200  based on the inlet temperature of the oxidation catalyst  200  detected by the temperature detector  210  at the normal driving mode, and may calculate the natural desulfurization degree by integrating the desulfurization efficiency according to the inlet temperature of the oxidation catalyst  20  to time or distance. Therefore, the control portion  300  can estimate actual sulfur-poisoning of the oxidation catalyst  200 . 
         [0068]    If the predetermined desulfurization period (e.g., 15,000 km) is reached, the control portion  300  resets the predetermined desulfurization period by increasing it (e.g., to be 17,000 km) according to the actual sulfur-poisoning of the oxidation catalyst  200 , and controls the desulfurization of the oxidation catalyst  200  according to the reset desulfurization period. 
         [0069]    Therefore, since post-injection for increasing exhaust gas temperature may not be performed frequently due to extension of the desulfurization period, fuel economy may be enhanced and noxious exhaust gas emission may be reduced. 
         [0070]    The control portion  300  calculates the desulfurization efficiency according to the inlet temperature of the oxidation catalyst  200  based on the graph illustrated in  FIG. 7 . 
         [0071]    In addition, the control portion  300  can estimate the inlet temperature of the oxidation catalyst  200  from a driving condition of the engine  100 . 
         [0072]    A method for desulfurizing an oxidation catalyst according to various embodiments of the present invention will be described in detail. 
         [0073]    If the engine  100  begins to operate at a step S 101  the control portion  300  integrates driving time by using a counter and travel distance (mileage) by using an integrating meter at a step S 102 . 
         [0074]    The control portion  300  can receive information about the driving time and the travel distance from a trip computer. 
         [0075]    In addition, the control portion  300  detects temperature of the exhaust gas passing through the inlet of the oxidation catalyst  200  by using the temperature detector  210  at a step S 103 , and determines whether the inlet temperature of the oxidation catalyst  200  is higher than the predetermined desulfurization temperature (e.g., 450° C.) at a step S 104 . That is, the control portion  300  determines whether the natural desulfurization occurs. 
         [0076]    If the inlet temperature of the oxidation catalyst  200  is not higher than the predetermined desulfurization temperature (e.g., 450° C.) at the step S 104 , the control portion  300  returns to the step S 102 . 
         [0077]    If the inlet temperature of the oxidation catalyst  200 , however, is higher than the predetermined desulfurization temperature (e.g., 450° C.) by effects of various driving environments at the step S 104 , the control portion  300  integrates a time or a distance where the inlet temperature of the oxidation catalyst  200  is higher than the predetermined desulfurization temperature (e.g., 450° C.) at a step S 105 . 
         [0078]    That is, a time or a distance where the natural desulfurization occurs is integrated. 
         [0079]    After that, the control portion  300  analyzes information transmitted from the integrating meter, the trip computer or the counter and determines whether the predetermined desulfurization period (e.g., 15,000 km) is reached at a step S 106 . 
         [0080]    If the predetermined desulfurization period (e.g., 15,000 km) is not reached at the step S 106 , the control portion  300  returns to the step S 102 . If the predetermined desulfurization period (e.g., 15,000 km), on the contrary, is reached at the step S 106 , the control portion reflects a value corresponding to the integrated time or the integrated distance where the inlet temperature of the oxidation catalyst  200  is higher than the desulfurization temperature (e.g., 450° C.) on a predetermined desulfurization time (e.g., 5 min.) at a step S 107 , and resets desulfurization time at a step S 108 . 
         [0081]    That is, the control portion  300  determines that the natural desulfurization of the oxidation catalyst  200  occurs during the integrated time or the integrated distance where the inlet temperature of the oxidation catalyst  200  is higher than the desulfurization temperature (e.g., 450° C.) at the normal driving mode, and shortens the desulfurization time by subtracting the value corresponding to the time or the distance where the natural desulfurization occurs from the predetermined desulfurization time (e.g., 5 min.). 
         [0000]        t   new (reset desulfurization time)= t (predetermined desulfurization time)−Δ t (value corresponding to time where natural desulfurization occurs)
 
         [0082]    If the desulfurization time is reset, the control portion  300  controls the post-injection according to the reset desulfurization time so as to increase the temperature of the exhaust gas. Since the inlet temperature of the oxidation catalyst  200  becomes higher than the desulfurization temperature (e.g., 450° C.), the sulfur poisoned at the oxidation catalyst  200  is removed and the oxidation catalyst  200  is regenerated at a step S 109 . In this patent, the regeneration of the oxidation catalyst  200  means that the sulfur poisoned at the oxidation catalyst  200  is removed by the hot exhaust gas. 
         [0083]    After that, if the desulfurization of the oxidation catalyst  200  is performed for the reset desulfurization time, the control portion  300  determines that the regeneration of the oxidation catalyst  200  is completed and returns to the initial step. 
         [0084]    Therefore, since the desulfurization time for removing the sulfur poisoned at the oxidation catalyst  200  is minimized, fuel economy may be enhanced and noxious exhaust gas may be reduced. 
         [0085]    As shown in  FIG. 3 , the desulfurization of a conventional vehicle is performed for the predetermined desulfurization time t (e.g., 5 min.) at every predetermined desulfurization period (e.g., 15,000 km). However, if the predetermined desulfurization period (e.g., 15,000 km) is reached according to various embodiments of the present invention, it is determined that the natural desulfurization of the oxidation catalyst  200  occurs for the integrated time At where the inlet temperature of the oxidation catalyst  200  is higher than the desulfurization temperature (e.g., 450° C.). 
         [0086]    Therefore, the desulfurization time is reset to the reduced desulfurization time t−Δt by subtracting the integrated time Δt where the natural desulfurization occurs from the predetermined desulfurization time t, and the desulfurization is performed. 
         [0087]    If the engine  100  begins to operate at a step S 201 , the control portion  300  integrates the driving time and the travel distance at a step S 202 . 
         [0088]    The control portion  300  detects the temperature of the exhaust gas passing through the inlet of the oxidation catalyst  200  by using the temperature detector  210  at a step S 203 , and determines whether the inlet temperature of the oxidation catalyst  200  is higher than the predetermined desulfurization temperature (e.g., 450° C.) at a step S 204 . 
         [0089]    If the inlet temperature of the oxidation catalyst  200  is not higher than the predetermined desulfurization temperature (e.g., 450° C.) at the step S 204 , the control portion  300  returns to the step S 202 . 
         [0090]    If the inlet temperature of the oxidation catalyst  200 , however, is higher than the predetermined desulfurization temperature (e.g., 450° C.) at the step S 204 , the control portion  300  integrates the time or the distance where the inlet temperature of the oxidation catalyst  200  is higher than the predetermined desulfurization temperature (e.g., 450° C.) at a step S 205 . 
         [0091]    After that, the control portion  300  determines whether the predetermined desulfurization period (e.g., 15,000 km) is reached at a step S 206 . 
         [0092]    If the predetermined desulfurization period (e.g., 15,000 km) is not reached at the step S 206 , the control portion  300  returns to the step S 202 . 
         [0093]    If the predetermined desulfurization period (e.g., 15,000 km), however, is reached at the step S 206 , the control portion  300  reflects the value corresponding to the integrated time or the integrated distance where the inlet temperature of the oxidation catalyst  200  is higher than the desulfurization temperature (e.g., 450° C.) at the normal driving mode on the predetermined desulfurization period (e.g., 15,000 km) at a step S 207 , and resets the desulfurization period to increase at a step S 208 . 
         [0094]    That is, the desulfurization period is increased by adding the integrated time or the integrated distance where the natural desulfurization of the oxidation catalyst  200  occurs to the predetermined desulfurization period. 
         [0000]        T (reset desulfurization period)= T (predetermined desulfurization period)+ T (predetermined desulfurization period)×Δ t (value corresponding to time where natural desulfurization occurs normal driving mode)/ t (predetermined desulfurization time)
 
         [0095]    After that, the control portion  300  determines whether the reset desulfurization period is reached at a step S 209 . If the reset desulfurization period is reached at the step S 209 , the control portion  300  performs the desulfurization of the oxidation catalyst  200  for the predetermined desulfurization time (e.g., 5 min.) through the post-injection at a step S 210 . 
         [0096]    After that, if the desulfurization of the oxidation catalyst  200  is completed, the control portion  300  determines that the regeneration of the oxidation catalyst  200  is completed and returns to the initial step. 
         [0097]    Therefore, since the desulfurization of the oxidation catalyst  200  for removing the poisoned sulfur does not occur frequently, fuel economy may be enhanced and noxious exhaust gas emission may be reduced. 
         [0098]    As shown in  FIG. 5 , the desulfurization of a conventional vehicle is performed for the predetermined desulfurization time t (e.g., 5 min.) at every predetermined desulfurization period (e.g., 15,000 km). However, the desulfurization period B (e.g., 17,000 km) is reset by reflecting the integrated time where the inlet temperature of the oxidation catalyst  200  is higher than the desulfurization temperature (e.g., 450° C.) on the desulfurization period according to various embodiments of the present invention. After that, if the reset desulfurization period B is reached, the desulfurization is performed for the predetermined desulfurization time b. Herein, the predetermined desulfurization times a and b may be the same or be different. 
         [0099]    With reference to  FIG. 6 , if the engine  100  begins to operate at a step S 301 , the control portion  300  integrates the driving time and the travel distance at a step S 302 . 
         [0100]    In addition, the control portion  300  detects the temperature of the exhaust gas passing through the inlet of the oxidation catalyst  200  by using the temperature detector  210  at a step S 303 , and calculates the desulfurization efficiency according to the inlet temperature of the oxidation catalyst  200  by using characteristic graph shown in  FIG. 7  at a step S 304 . 
         [0101]    After that, the control portion  300  integrates the desulfurization efficiency according to the inlet temperature of the oxidation catalyst  200  to time or distance at a step S 305  and calculates natural desulfurization degree occurring at the normal driving mode at a step S 306 . 
         [0102]    The control portion  300  determines whether the predetermined desulfurization period (e.g., 15,000 km) is reached at a step S 307 . 
         [0103]    If the predetermined desulfurization period (e.g., 15,000 km) is not reached at the step S 307 , the control portion  300  returns to the step S 302 . 
         [0104]    If the predetermined desulfurization period (e.g., 15,000 km), however, is reached at the step S 307 , the control portion  300  resets the desulfurization time by reflecting the integrated desulfurization efficiency on the predetermined desulfurization time (e.g., 5 min.) at a step S 308 . 
         [0105]    That is, the control portion  300  subtracts a value corresponding to the natural desulfurization degree occurring at the normal driving mode from the predetermined desulfurization time (e.g., 5 min.) and resets the desulfurization time to be shortened. 
         [0106]    If the desulfurization time is reset, the control portion  300  raises the temperature of the exhaust gas according to the reset desulfurization time through the post-injection. Since the inlet temperature of the oxidation catalyst  200  becomes higher than the desulfurization temperature (e.g., 450° C.), the sulfur poisoned at the oxidation catalyst  200  is removed and the oxidation catalyst  200  is regenerated at a step S 309 . 
         [0107]    After that, if the desulfurization of the oxidation catalyst  200  is performed for the reset desulfurization time, the control portion  300  determines that the regeneration of the oxidation catalyst  200  is completed and returns to the initial step. 
         [0108]    Therefore, since the desulfurization time for regenerating the oxidation catalyst  200  is shortened, fuel economy may be enhanced and noxious exhaust gas emission may be reduced. 
         [0109]    Reduction of the desulfurization time according to other exemplary embodiments is similar to that according to that described above, and thus detailed description will be omitted. 
         [0110]    With reference to  FIG. 8 , if the engine  100  begins to operate at a step S 401 , the control portion  300  integrates the driving time and the travel distance at a step S 402 . 
         [0111]    The control portion  300  detects the inlet temperature of the oxidation catalyst  200  by using the temperature detector  210  at a step S 403 , and calculates the desulfurization efficiency according to the inlet temperature of the oxidation catalyst  200  by using the characteristic graph shown in  FIG. 7  at a step S 404 . 
         [0112]    After that, the control portion  300  integrates the desulfurization efficiency according to the inlet temperature of the oxidation catalyst  200  to time or distance at a step S 405  and calculates the natural desulfurization degree occurring at the normal driving mode at a step S 406 . 
         [0113]    The control portion  300  determines whether the predetermined desulfurization period (e.g., 15,000 km) is reached at a step S 407 . 
         [0114]    If the predetermined desulfurization period (e.g., 15,000 km) is not reached at the step S 407 , the control portion  300  returns to the step S 402 . 
         [0115]    If the predetermined desulfurization period (e.g., 15,000 km), however, is reached at the step S 407 , the control portion  300  reflects the integrated desulfurization efficiency on the predetermined desulfurization period (e.g., 15,000 km) and resets the desulfurization period at a step S 408 . 
         [0116]    That is, the control portion  300  adds a value corresponding to the natural desulfurization degree occurring at the normal driving mode to the predetermined desulfurization period and resets the desulfurization period to increase. 
         [0117]    If the desulfurization period is reset, the control portion  300  determines whether the reset desulfurization period is reached at a step S 409 . 
         [0118]    If the reset desulfurization period is not reached at the step S 409 , the control portion  300  determines whether the reset desulfurization period is reached continuously. 
         [0119]    After that, if the reset desulfurization period is reached, the control portion  300  raises the temperature of the exhaust gas through the post-injection for the predetermined desulfurization time (e.g., 5 min.). Since the inlet temperature of the oxidation catalyst  200  becomes higher than the desulfurization temperature (e.g., 450° C.), the sulfur poisoned at the oxidation catalyst  200  is removed and the oxidation catalyst  200  is regenerated at a step S 410 . 
         [0120]    After that, if the desulfurization of the oxidation catalyst  200  is performed for the predetermined desulfurization time, the control portion  300  determines that the regeneration of the oxidation catalyst  200  is completed and returns to the initial step. 
         [0121]    Therefore, since the desulfurization for regenerating the oxidation catalyst  200  does not occur frequently, fuel economy may be enhanced and noxious exhaust gas emission may be reduced. 
         [0122]    Increase of desulfurization according to other embodiments is similar to that according to that described above, and thus detailed description will be omitted. 
         [0123]    Since natural desulfurization degree occurring at various driving environments is reflected on desulfurization time or desulfurization period, fuel economy may be enhanced and noxious exhaust gas emission may be reduced according to various embodiments of the present invention. 
         [0124]    Desulfurization time is shortened or desulfurization period is extended according to natural desulfurization degree, but reduction of the desulfurization time and increase of the desulfurization period can be simultaneously performed. Therefore, it is to be understood that the scope of the present invention includes that the reduction of the desulfurization time and the increase of the desulfurization period are simultaneously performed. 
         [0125]    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.