Abstract:
An exhaust passageway of the internal combustion engine is formed of a single exhaust pipe  5 . A portion  11   b  configuring a passageway through which the exhaust gas passes and a portion  11   c  provided with a catalyst  11   e  heating up the exhaust gas by emitting heat upon being supplied with a reducing agent, are provided in parallel so as to share a section of the single exhaust pipe with each other on an upstream side  11  of an exhaust gas purifying device  10  in the exhaust pipe  5 . In the exhaust gas flowing through the exhaust pipe  5 , allocation of a quantity of the exhaust gas passing through the catalyst  11   e  and a quantity of the exhaust gas passing through the passageway  11   b , is set changeable.

Description:
[0001]    This is a 371 national phase application of PCT/JP2006/307008 filed 28 Mar. 2006, claiming priority to Japanese Patent Application No. JP 2005-091485 filed 28 Mar. 2005, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an exhaust gas purifying system of an internal combustion engine. 
       BACKGROUND OF THE INVENTION 
       [0003]    An exhaust gas from an internal combustion engine contains harmful substances such as NOx (nitrogen oxide). It is known that a NOx catalyst for purifying the exhaust gas of NOx is provided in an exhaust system of the internal combustion engine in order to decrease emissions of these harmful substances. In this technology, when a temperature of the NOx catalyst is low, there might be a case that a NOx purifying efficiency decreases. Accordingly, the temperature of the NOx catalyst needs increasing up to a temperature at which the exhaust gas can be sufficiently purified of NOx. 
         [0004]    On the other hand, the exhaust gas from the internal combustion engine contains particulate matters (PM) of which a main component is carbon. A known technology for preventing the emissions of these particulate matters into the atmospheric air involves providing an exhaust system of the internal combustion engine with a particulate filter (which will hereinafter simply be termed a [filter]) for trapping (scavenging) the particulate matters. 
         [0005]    In this type of filter, when a deposition quantity of the trapped particulate matters rises, a backpressure in the exhaust gas increases due to clogging of the filter, and engine performance declines. To cope with this, a temperature of the filter is raised by increasing the temperature of the exhaust gas introduced into the filter, and the trapped particulate matters are removed by oxidation, thus scheming to regenerate the exhaust gas purifying performance of the filter (which will hereinafter be referred to as a [PM regenerating process]). 
         [0006]    In the above PM regenerating process, when the temperature of the filter is low, there might be a case of being unable to sufficiently oxidation-remove the particulate matters trapped by the filter. Accordingly, in this case also, the filter temperature needs increasing up to the temperature at which the particulate matters trapped by the filter can be sufficiently removed by oxidation. 
         [0007]    In this respect, as disclosed in Japanese Patent Application Laid-Open Publication No. 2003-166417, such a technology is proposed that there are provided a filter, an oxidation catalyst disposed on an upstream side of the filter and a bypath via which the exhaust gas bypasses the oxidation catalyst, and the filter is warmed up as soon as possible when executing the PM regenerating process by switchover as to which way, the bypath or the oxidation catalyst, the exhaust gas should pass through. Alternatively, as disclosed in published Japanese translations of PCT international publication for patent applications No. 2003-533626, a technology is proposed, wherein a catalyst-type burner and a fuel adding device are provided upstream of the filter, and the PM regenerating process can be executed surely at a low cost. 
         [0008]    Herein, in the former technology, there was a case in which when the exhaust gas passed through the bypath, the temperature of the exhaust gas decreased, and the filter temperature was hard to rise efficiently. Further, in the latter technology, during a normal operation of the internal combustion engine, the catalyst-type burner dissipated a great amount of exhaust heat, and there was a possibility that the filter temperature might be decreased. 
       SUMMARY OF INVENTION 
       [0009]    It is an object of the present invention to provide a technology capable of increasing the temperature of an exhaust gas purifying device in an exhaust system of an internal combustion engine more efficiently or more surely with a much simpler configuration. 
         [0010]    The following is a greatest feature of the present invention for accomplishing the above object. An exhaust passageway of the internal combustion engine is formed of a single exhaust pipe on an upstream side of the exhaust gas purifying device, and a portion configuring a passageway through which the exhaust gas passes and a portion provided with a catalyst heating up the exhaust gas by emitting heat upon being supplied with a reducing agent, are provided in parallel with each other in the exhaust pipe. Then, in the exhaust gas flowing through the exhaust pipe, allocation of a quantity of the exhaust gas passing through the catalyst heating up the exhaust gas and a quantity of the exhaust gas passing through the passageway, is set changeable. 
         [0011]    More specifically, in an exhaust gas purifying system of an internal combustion engine, comprising: 
         [0012]    an exhaust gas purifying device provided in an exhaust passageway of the internal combustion engine, purifying an exhaust gas passing through the exhaust passageway and heated up to a predetermined temperature or higher with the result that purifying capability thereof is improved; 
         [0013]    exhaust gas temperature increasing unit provided on an upstream side of the exhaust gas purifying device in the exhaust passageway; and 
         [0014]    reducing agent adding unit provided on the upstream side of the exhaust gas temperature increasing unit in the exhaust passageway and adding a reducing agent to the exhaust gas passing through the exhaust passageway, 
         [0015]    an improvement is characterized in that the exhaust gas temperature increasing unit includes: 
         [0016]    an exhaust gas temperature increasing catalyst provided in a single exhaust pipe configuring the exhaust passageway so that an exhaust gas flow-through area trough which the exhaust gas should pass is left, supplied with the reducing agent added from the reducing agent adding unit and thereby emitting heat; and 
         [0017]    an exhaust gas flowrate control device controlling, in the exhaust gas passing though the exhaust pipe, allocation of a quantity of the exhaust gas passing the exhaust gas flow-through area and a quantity of the exhaust gas passing through the exhaust gas temperature increasing catalyst. 
         [0018]    Herein, in the case of purifying the exhaust gas of the NOx by the NOx catalyst provided in the exhaust system of the internal combustion engine, the NOx catalyst needs to have a temperature equal to or higher than an activation temperature at which the NOx can be occluded. Further, in the case of executing the PM regenerating process on the filter provided in the exhaust system, it is required that a temperature of the filter be kept equal to or higher than a temperature at which the particulate matters trapped by the filter can be removed by oxidation. 
         [0019]    Then, for attaining this, there might be a case of taking a method by which the exhaust gas temperature increasing catalyst for increasing the temperature of the exhaust gas flowing into the NOx catalyst or the filter is provided on the upstream side of the NOx catalyst or the filter, and the temperature of the exhaust gas flowing into the NOx catalyst or the filter is increased by reaction heat generated by supplying the reducing agent to this exhaust gas temperature increasing catalyst. 
         [0020]    In such a case, if a heat retaining property of the exhaust gas temperature increasing catalyst itself is insufficient, even when supplying the reducing agent to the exhaust gas temperature increasing catalyst, there was a possibility that the temperature of the exhaust gas flowing into the NOx catalyst or the filter could not be amply increased. 
         [0021]    Further, for example, if the temperature of the NOx catalyst or the filter is high, there might occur such a case that the exhaust gas not passing through the exhaust gas temperature increasing catalyst is to flow directly into the NOx catalyst or the filter. For attaining this, it is considered that a bypath via which the exhaust gas bypasses the exhaust gas temperature increasing catalyst is provided separately from the exhaust pipe. In this case, however, the exhaust passageway comes to have a complicated structure, and there was a possibility that mountability on a vehicle declines or it becomes difficult to reduce costs. 
         [0022]    Such being the case, according to the present invention, the exhaust gas temperature increasing unit is provided on the upstream side of the exhaust gas purifying device in the exhaust passageway. Then, in the exhaust gas temperature increasing unit, the exhaust gas temperature increasing catalyst is provided in the single exhaust pipe configuring the exhaust passageway so as to occupy part of the section of the exhaust pipe, and a remaining area of the section of the exhaust pipe is set as the exhaust gas flow-through area through which the exhaust gas passes. Then, the exhaust gas flow rate control device can control, in the exhaust gas flowing through the exhaust pipe, the allocation of the quantity of the exhaust gas passing through the exhaust gas flow-through area and the quantity of the exhaust gas passing through the exhaust gas temperature increasing catalyst. 
         [0023]    With this contrivance, the exhaust gas temperature increasing catalyst and the exhaust gas flow-through area can be formed in parallel with each other in an interior of the single exhaust pipe configuring the exhaust passageway, and hence a contact area between the exhaust gas temperature increasing catalyst and the external portion of the exhaust passageway can be decreased to the greatest possible degree. Further, when the exhaust gas passes through the exhaust gas flow-through area, the heat of the exhaust gas can be efficiently transferred to the exhaust gas temperature increasing catalyst. As a result thereof, the heat retaining property of the exhaust gas temperature increasing catalyst can be improved. 
         [0024]    Moreover, both of the exhaust gas temperature increasing catalyst and the exhaust gas flow-through area through which the exhaust gas passes can be provided in the single exhaust pipe, and the structure can be thus simplified, whereby the mountability of the exhaust gas purifying system on the vehicle can be improved, and the cost reduction can be also attained. 
         [0025]    Furthermore, according to the present invention, the exhaust gas flow-through area may be disposed in a central portion in section perpendicular to an exhaust gas pass-through direction in the exhaust pipe, and the exhaust gas temperature increasing catalyst may be disposed outwardly of the exhaust gas flow-through area within the section. 
         [0026]    Herein, if the exhaust gas warmed up by the exhaust gas temperature increasing catalyst uniformly flows to an upstream-sided edge surface of the exhaust gas purifying device, the temperature of the exhaust gas purifying device tends to be high at its central portion and becomes lower as it gets closer to a peripheral portion thereof. This is attributed to an escape of the heat into the outside air from the outer peripheral portion of the exhaust gas purifying device. 
         [0027]    By contrast, according to the present invention, the exhaust gas flow-through area through which the exhaust gas passes is disposed at the central portion in the section perpendicular to an exhaust gas pass-through direction in the exhaust pipe, and the exhaust gas temperature increasing catalyst is disposed outside of the exhaust gas flow-through area within the section. With this arrangement, the exhaust gas temperature increasing catalyst can be distributed over the outer peripheral portion in the section perpendicular to the exhaust gas pass-through direction in the exhaust pipe. This contrivance being thus made, the exhaust gas heated up by the exhaust gas temperature increasing catalyst can be supplied concentratedly to the outer peripheral portion of the exhaust gas purifying device, and, even when the heat escapes into the outside air from the outer peripheral portion of the exhaust gas purifying device, the temperature of the exhaust gas purifying device can be increased uniformly. 
         [0028]    Further, according to the present invention, the exhaust gas flow rate control device may be set capable of selecting, by controlling the allocation, a state where substantially an entire quantity of the exhaust gas flowing through the exhaust pipe passes through the exhaust gas flow-through area, a state where substantially the entire quantity of the exhaust gas flowing through the exhaust pipe passes through the exhaust gas temperature increasing catalyst, and a state where substantially the entire quantity of the exhaust gas flowing through the exhaust pipe passes through both of the exhaust gas flow-through area and the exhaust gas temperature increasing catalyst. 
         [0029]    This contrivance being thus made, the exhaust gas flow rate control device selects the state where substantially the entire quantity of the exhaust gas flowing through the exhaust pipe passes through the exhaust gas temperature increasing catalyst, and the reducing agent adding unit adds the reducing agent to the exhaust gas, whereby the exhaust gas temperature increasing catalyst is supplied with the entire quantity of the exhaust gas and can get the reducing reaction caused by the reducing agent. This enables an inflow of only the high-temperature exhaust gas into the exhaust gas purifying device. 
         [0030]    Further, the exhaust gas flow rate control device selects the state where substantially the entire quantity of the exhaust gas flowing through the exhaust pipe passes through the exhaust gas flow-through area, whereby the exhaust gas can be flowed directly into the exhaust gas purifying device without passing through the exhaust gas temperature increasing catalyst. With this contrivance, if the exhaust temperature of the exhaust gas discharged from the internal combustion engine is high such as when in a high-load operation, the exhaust gas purifying device can be heated up by a thermal energy of the exhaust gas. Further, when the temperature of the exhaust gas purifying device is high and in a low-load operation, the exhaust gas temperature increasing catalyst can be restrained from becoming an excessively high temperature by flowing a comparatively low-temperature exhaust gas directly into the exhaust gas purifying device. 
         [0031]    Moreover, if the temperature of the exhaust gas discharged from the internal combustion engine is high such as when in the high-load operation and if the temperature of the exhaust gas temperature increasing catalyst has already been high, the high-temperature exhaust gas can be restrained from further flowing into the exhaust gas temperature increasing catalyst. This makes it possible to restrain the exhaust gas temperature increasing catalyst from becoming the excessively high temperature. In addition, if the temperature of the exhaust gas discharged from the internal combustion engine is low such as when in the low-load operation, the low-temperature exhaust gas can be restrained from flowing into the exhaust gas temperature increasing catalyst. This makes it feasible to restrain the decrease in temperature of the exhaust gas temperature increasing catalyst. 
         [0032]    Moreover, the exhaust gas flow rate control device selects the state where the exhaust gas flowing through the exhaust pipe passes through both of the exhaust gas flow-through area and the exhaust gas temperature increasing catalyst, whereby the exhaust gas heated up as it passes through the exhaust gas temperature increasing catalyst and the exhaust gas not passing through the exhaust gas temperature increasing catalyst can be flowed in a properly mixed state thereof into the exhaust gas purifying device. This enables improvement of controllability of the temperature of the exhaust gas purifying device. 
         [0033]    Furthermore, according to the present invention, when heating up the exhaust gas purifying device, 
         [0034]    the reducing agent adding unit may add the reducing agent to the exhaust gas passing through the exhaust passageway, and the exhaust gas flow rate control device may control the allocation in order to make substantially the entire quantity of the exhaust gas flowing through the exhaust pipe pass through the exhaust gas temperature increasing catalyst, and 
         [0035]    the exhaust gas flow rate control device may, after the reducing agent added from the reducing agent adding unit has reached the exhaust gas temperature increasing catalyst, control the allocation in order to decrease, in the exhaust gas flowing through the exhaust pipe, the quantity of the exhaust gas passing through the exhaust gas temperature increasing catalyst. 
         [0036]    Namely, in the case of heating up the exhaust gas purifying device as described above, it is desirable that the high-temperature exhaust gas be flowed into the exhaust gas purifying device. For attaining this, the reducing agent adding unit adds the reducing agent to the exhaust gas flowing through the exhaust passageway, and the exhaust gas flow rate control device controls the allocation in order for the exhaust gas temperature increasing catalyst to admit the passage of substantially the entire quantity of the exhaust gas flowing trough the exhaust pipe. Under this control, the reducing agent added from the reducing agent adding unit can be efficiently led to the exhaust gas temperature increasing catalyst. 
         [0037]    Then, after the reducing agent added from the reducing agent adding unit has reached the exhaust gas temperature increasing catalyst, the exhaust gas flow rate control device controls, in the exhaust gas flowing through the exhaust pipe, the allocation in order to decrease the quantity of the exhaust gas passing through the exhaust gas temperature increasing catalyst. The allocation being thus controlled, after the reducing agent has reached the exhaust gas temperature increasing catalyst, the flow rate of the exhaust gas passing though the exhaust gas temperature increasing catalyst decreases, and therefore the reducing agent can be restrained from passing intact through the exhaust gas temperature increasing catalyst. Then, the reducing agent can be stayed for a sufficiently long period of time in the exhaust gas temperature increasing catalyst. As a result, the sufficient reducing reaction can be caused in the exhaust gas temperature increasing catalyst, and the temperature of the exhaust gas discharged from the exhaust gas temperature increasing catalyst can be increased more surely. 
         [0038]    Further, according to the present invention, the exhaust gas flow rate control device may, during a decelerating operation of a vehicle mounted with the internal combustion engine, control the allocation in order to decrease, in the exhaust gas flowing through the exhaust pipe, the quantity of the exhaust gas passing through the exhaust gas temperature increasing catalyst. 
         [0039]    Herein, during a decelerating operation of the internal combustion engine, there is a case where the temperature of the exhaust gas discharged from the internal combustion engine decreases. Then, in such a case, when the low-temperature exhaust gas passes through the exhaust gas temperature increasing catalyst, the temperature of the exhaust gas temperature increasing catalyst decreases, and there is a possibility that the temperature of the exhaust gas becomes hard to increase efficiently. Herein, the exhaust gas temperature increasing catalyst often has a smaller thermal capacity than the exhaust gas purifying device has, and hence there are many cases in which the temperature thereof especially tends to decrease due to the passage of the low-temperature exhaust gas. 
         [0040]    By contrast, during the decelerating operation of the vehicle mounted with the internal combustion engine, the exhaust gas flow rate control device may, in the exhaust gas flowing through the exhaust pipe, decrease the quantity of the exhaust gas passing through the exhaust gas temperature increasing catalyst. With this operation, if the temperature of the exhaust gas discharged from the internal combustion engine is low, it is possible to decrease the quantity of the exhaust gas passing through the exhaust gas temperature increasing catalyst and to restrain the drop in temperature of the exhaust gas temperature increasing catalyst. 
         [0041]    It should be noted that the means for solving the problems in the invention can be used by combining these means as much as possible. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0042]      FIG. 1  is a view showing an internal combustion engine according to a first embodiment of the present invention and showing outlines of configurations of an exhaust system and a control system thereof; 
           [0043]      FIG. 2  is a flowchart showing an exhaust gas purifying device temperature increasing routine in the first embodiment of the present invention; 
           [0044]      FIG. 3  is a flowchart showing another example of the exhaust gas purifying device temperature increasing routine in the first embodiment of the present invention; 
           [0045]      FIG. 4  is a view showing an exhaust gas temperature increasing device according to a second embodiment of the present invention and showing an outline of configuration of an exhaust gas purifying device; 
           [0046]      FIG. 5  is a view showing the exhaust gas temperature increasing device according to the second embodiment of the present invention and showing another mode of the outline of configuration of the exhaust gas purifying device; and 
           [0047]      FIG. 6  is a view showing the exhaust gas temperature increasing device according to the second embodiment of the present invention and showing still another mode of the outline of configuration of the exhaust gas purifying device. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]    An in-depth description of a best mode for carrying out the present invention will hereinafter be given in an exemplifying manner with reference to the drawings. 
       First Embodiment 
       [0049]      FIG. 1  is a view showing an internal combustion engine according to a first embodiment and showing outlines of configurations of an exhaust system and a control system thereof. An internal combustion engine  1  shown in  FIG. 1  is classified as a diesel engine. Note that an interior of the internal combustion engine  1  and an intake system thereof are omitted in  FIG. 1 . 
         [0050]    In  FIG. 1 , an exhaust pipe  5 , through which an exhaust gas discharged from the internal combustion engine  1  flows, is connected to the internal combustion engine  1  and is further connected downstream to an unillustrated silencer. Moreover, an exhaust gas purifying device  10 , which purifies the exhaust gas from NOx and particulate matters (e.g., soot), is disposed downstream in the exhaust pipe  5 . Then, an exhaust gas temperature increasing device  11 , which increases the temperature of the exhaust gas purifying device  10  by increasing a temperature of the exhaust gas flowing into the exhaust gas purifying device  10 , is disposed upstream of the exhaust gas purifying device  10  in the exhaust pipe  5 . 
         [0051]    This exhaust gas temperature increasing device  11  is partitioned by a partition pipe  11   a  having approximately the same diameter as a diameter of the exhaust pipe  5  off into an internal pipe portion  11   b  and an external pipe portion  11   c . Then, the internal pipe portion  11   b  is provided with a flow rate control valve  11   d  that determines how a flow rate of the exhaust gas flowing through the internal pipe portion  11   b  and a flow rate of the exhaust gas flowing through the external pipe portion  11   c  are allocated by changing a flow rate of the exhaust gas passable through the internal pipe portion  11   b . Further, the external pipe portion  11   c  is provided with an oxidation catalyst  11   e  having oxidation capability so that the external pipe portion  11   c  is filled with the oxidation catalyst  11   e . Moreover, a fuel adding valve  12  for adding a fuel as a reducing agent to the exhaust gas flowing through the exhaust pipe  5  is disposed on the upstream side of the exhaust gas temperature increasing device  11  in the exhaust pipe  5 . 
         [0052]    Herein, the exhaust gas temperature increasing device  11  corresponds to exhaust gas temperature increasing unit. Further, the oxidation catalyst  11   e  corresponds to an exhaust gas temperature increasing catalyst. Moreover, the internal pipe portion  11   b  corresponds to an exhaust gas flow-through area. The fuel adding valve  12  corresponds to reducing agent adding unit. Still further, the flow rate control valve  11   d  configures an exhaust gas flow rate control device. 
         [0053]    The exhaust gas purifying device  10  in the first embodiment is a device constructed so that a wall-flow type filter composed of a porous base material supports an oxidation catalyst typified by platinum (Pt) and NOx occlusion agent typified by potassium (K) and cesium (Cs). The exhaust gas purifying device  10  does not necessarily have to, however, be a device that support the NOx occlusion agent, wherein, for example, the NOx catalyst may be separately independently provided in the exhaust pipe  5 . 
         [0054]    In the thus-constructed internal combustion engine  1  and the exhaust system thereof, an electronic control unit (ECU)  35  for controlling the internal combustion engine  1  and the exhaust system, is provided. This ECU  35  is a unit for performing, in addition to controlling an operating state etc of the internal combustion engine  1  in accordance with operating conditions of the internal combustion engine  1  and in response to a request of a driver, the control of an exhaust gas purifying system including the exhaust gas purifying device  10 , the exhaust gas temperature increasing device  11  and the fuel adding valve  12 . 
         [0055]    Unillustrated sensors related to the control of the operating state of the internal combustion engine  1 , such as an airflow meter, a crank position sensor and an accelerator position sensor, are connected via electric wirings to the ECU  35 , wherein output signals of these sensors are inputted to the ECU  35 . On the other hand, an unillustrated fuel injection valve etc for combustion in the internal combustion engine  1  is connected via the electric wiring to the ECU  35 , and, in addition, the flow rate control valve  11   d , the fuel adding valve  12  etc in the first embodiment are connected via the electric wirings to the ECU  35 , whereby these connected components are controlled. 
         [0056]    Further, the ECU  35  is equipped with a CPU (Central Processing Unit), a ROM (Read-Only Memory), a RAM (Random Access Memory) etc, wherein the ROM is preinstalled with programs for executing various categories of control of the internal combustion engine  1  and is stored with a map registered with data. The programs preinstalled in the ROM of the ECU  35  include, as one category of the program, a PM regenerating process routine (of which an explanation is omitted) for regenerating PM trapping (scavenging) capability of the exhaust gas purifying device  10 , a NOx reduction process routine for reducing and thus purifying the NOx occluded in the NOx catalyst in the exhaust gas purifying device  10 , similarly a SOx regenerating process routine (of which an explanation is omitted) for reducing and thus purifying SOx occluded in the NOx catalyst in the exhaust gas purifying device  10 , and, in addition, an exhaust gas purifying device temperature increasing routine in the first embodiment, which will be described later on. 
         [0057]    By the way, when starting up the internal combustion engine  1  according to the first embodiment, if a temperature of the exhaust gas purifying device  10  is low, there might be a case in which the NOx catalyst in the exhaust gas purifying device  10  does not yet reach an activation temperature and is therefore incapable of sufficiently purifying the NOx in the exhaust gas that is discharged from the internal combustion engine  1 . Then, the exhaust gas discharged from the internal combustion engine  1  is released without purifying the exhaust gas of the NOx, and such a possibility might arise that the emission is deteriorated. 
         [0058]    Such being the case, the first embodiment shall take such a contrivance that when starting up the internal combustion engine  1 , if the temperature of the exhaust gas purifying device  10  is low, a quantity of the exhaust gas passing though the internal pipe portion  11   b  is decreased or zeroed by driving the flow rate control valve  11   d  on a valve-closing side, and the fuel is added as a reducing agent from the fuel adding valve  12 . 
         [0059]    With this contrivance, the fuel added from the fuel adding valve  12  is efficiently supplied to the oxidation catalyst  11   e , and reducing reaction is efficiently caused in the oxidation catalyst  11   e , thereby increasing the temperature of the exhaust gas discharged from the oxidation catalyst  11   e . This operation enables the high-temperature exhaust gas to flow into the exhaust gas purifying device  10 , whereby the exhaust gas purifying device  10  can be immediately warmed up. 
         [0060]    On this occasion, in the first embodiment, the exhaust gas temperature increasing device  11  is disposed within the exhaust pipe  5  without branching the exhaust pipe  5  configuring an exhaust passageway. To be specific, the internal pipe portion  11   b  and the external pipe portion  11   c  are provided within the exhaust pipe  5 , and the oxidation catalyst  11   e  is disposed so that the external pipe portion  11   c  is filled with the oxidation catalyst  11   e . With this contrivance, as compared with a configuration of branching off into the exhaust passageway containing the oxidation catalyst and a bypath, the exhaust gas temperature increasing device  11  can be downsized on the whole, and mountability onto a vehicle can be improved. Further, cost reduction can be attained. Still further, the exhaust gas temperature increasing device  11  takes a configuration that makes it harder for the heat of reaction that is generated in the oxidation catalyst  11   e  to effuse outside than in the configuration of branching off into the exhaust passageway containing the oxidation catalyst and the bypath, and hence a heat retaining property of the oxidation catalyst  11   e  can be improved. 
         [0061]    Yet further, in the first embodiment, the oxidation catalyst  11   e  is disposed in the external pipe portion  11   c  within the exhaust pipe  5 , and therefore the high-temperature exhaust gas can be supplied concentratedly to an outer peripheral portion of a front edge surface of the exhaust gas purifying device  10 . As a result, a central portion of the front edge surface of the exhaust gas purifying device  10  can be restrained from having a excessively higher temperature than at the outer peripheral portion, whereby the exhaust gas purifying device  10  can be uniformly warmed up on the whole. 
         [0062]    Next, the detailed control on the occasion of warming up the exhaust gas purifying device  10  in the first embodiment will be explained.  FIG. 2  shows the exhaust gas purifying device temperature increasing routine in the first embodiment, and this is a routine for increasing a temperature of the NOx catalyst up to the activation temperature if the NOx catalyst of the exhaust gas purifying device  10  does not yet reach the activation temperature. This routine is executed by the ECU  35  at an interval of predetermined time during the operation of the internal combustion engine  1 . 
         [0063]    Upon executing this routine, to start with, in S 101 , a catalyst temperature T defined as the temperature of the NOx catalyst of the exhaust gas purifying device  10  is acquired. This catalyst temperature T may be deduced in a way that detects a temperature of cooling water of the internal combustion engine  1  by use of an unillustrated cooling water temperature sensor, and the temperature of the exhaust gas discharged from the exhaust gas purifying device  10  may also be detected directly by an unillustrated exhaust gas temperature sensor. Alternatively, a relationship between elapsed time since the startup of the internal combustion engine  1  has begun and the catalyst temperature T, is previously obtained, and the catalyst temperature T may also be deduced from the elapsed time since the startup of the internal combustion engine  1  has begun. When finishing the process in S 101 , the operation proceeds to S 102 . 
         [0064]    In S 102 , it is judged whether the catalyst temperature T is equal to or higher than the activation temperature of the NOx catalyst in the exhaust gas purifying device  10 . Then, when judging that the catalyst temperature T is equal to or higher than the activation temperature of the NOx catalyst in the exhaust gas purifying device  10 , the exhaust gas purifying device  10  is judged to be in a state capable of purifying the exhaust gas of the NOx that is discharged from the internal combustion engine  1 , and hence the operation proceeds to S 107 . 
         [0065]    In S 107 , the flow rate control valve  11   d  is fully opened. Through this valve opening, the exhaust gas discharged from the internal combustion engine  1  flows directly into the exhaust gas purifying device  10  and is purified of the NOx therein. 
         [0066]    While on the other hand, when judging in S 102  that the catalyst temperature T is lower than the activation temperature, the catalyst temperature T must be raised up to the activation temperature or higher as soon as possible, and therefore the operation proceeds to S 103 . In S 103 , the flow rate control valve  11   d  is fully closed. Through this operation, it follows that substantially an entire quantity of the exhaust gas from the internal combustion engine  1  flows into the oxidation catalyst  11   e . When terminating the process in S 103 , the operation proceeds to S 104 . 
         [0067]    In S 104 , the fuel serving as the reducing agent is added from the fuel adding valve  12  to the exhaust gas flowing through the exhaust pipe  5 . The fuel being thus added, it follows that the fuel added from the fuel adding valve  12  is carried together with substantially the entire quantity of exhaust gas getting to flow to the oxidation catalyst  11   e  and is thus supplied to the oxidation catalyst  11   e . When finishing the process in S 104 , the operation proceeds to S 105 . 
         [0068]    In S 105 , it is judged whether or not the fuel added from the fuel adding valve  12  reaches the oxidation catalyst  11   e . Herein, the judgment that the fuel added from the fuel adding valve  12  reaches the oxidation catalyst  11   e  may be made by reading, into the ECU  35 , an output of an unillustrated air-fuel ratio sensor provided upstream immediately of the oxidation catalyst  11   e , and may also be made by knowing that the temperature of the oxidation catalyst  11   e  starts abruptly increasing. Moreover, a relationship between the operating state of the internal combustion engine  1  and a period of time till the fuel added from the fuel adding valve  12  reaches the oxidation catalyst  11   e , is mapped beforehand, and the above judgment may be made based on whether or not there is an elapse of the time read from the map in accordance with the operating state of the internal combustion engine  1  when executing the exhaust gas purifying device temperature increasing routine since the fuel has been added from the fuel adding valve  12 . 
         [0069]    If it is judged in S 105  that the fuel does not yet reach the oxidation catalyst  11   e , the operation returns to a status before the process in S 105 , wherein it is again judged in S 105  whether the fuel added from the fuel adding valve  12  reaches the oxidation catalyst  11   e  or not. Then, the process in S 105  is repeatedly executed till judging that the fuel reaches the oxidation catalyst  11   e . Subsequently, when judging in S 105  that the fuel reaches the oxidation catalyst  11   e , the operation proceeds to S 106 . 
         [0070]    In S 106 , the full-close of the flow rate control valve  11   d  is cancelled, and the flow rate control valve  11   d  is opened to a predetermined opening degree. With this valve opening, the flow rate of the exhaust gas flowing to the oxidation catalyst  11   e  decreases. The operation being thus done, the fuel reaching the oxidation catalyst  11   e  can be restrained from passing intact through the oxidation catalyst  11   e  within a short period of time and can be made to stay within the oxidation catalyst  11   e  over a sufficient period of time. As a result, the temperature of the exhaust gas after passing through the oxidation catalyst  11   e  can be sufficiently increased, and the exhaust gas purifying device  10  can be heated up quickly. Further, a fuel consumption for heating up the exhaust gas purifying device  10  can be decreased. 
         [0071]    Herein, the predetermined opening degree is an opening degree capable of sufficiently restraining the fuel reaching the oxidation catalyst  11   e  from passing intact through the oxidation catalyst  11   e  and amply supplying the exhaust gas having its temperature increased in the oxidation catalyst  11   e  to the exhaust gas purifying device  10  in order to increase the temperature of the exhaust gas purifying device  10 . This predetermined opening degree may be previously mapped in relation with the operating state of the internal combustion engine land may be, when executing S 106 , derived by reading from the map the opening degree corresponding to the operating state of the internal combustion engine  1  on this occasion. When terminating the process in S 106 , the present routine is finished for the meantime. 
         [0072]    As discussed so far, the catalyst temperature increasing routine in the first embodiment is that if the temperature of the NOx catalyst in the exhaust gas purifying device  10  is lower than the activation temperature, the flow rate control valve  11   d  is fully closed, and the fuel is added into the exhaust gas from the fuel adding valve  12 , thereby making it possible to ensure transportability enough for having the added fuel reached the oxidation catalyst  11   e.    
         [0073]    Further, after the fuel has reached the oxidation catalyst  11   e , the flowrate control valve  11   d  is opened, and the exhaust gas from the internal combustion engine  1  flows to both of the external pipe portion  11   c  and the internal pipe portion  11   b , whereby the fuel reaching the oxidation catalyst  11   e  can be refrained from passing intact through the oxidation catalyst  11   e  within the short period of time, and the exhaust gas the temperature of which has been increased by the reducing reaction in the oxidation catalyst  11   e  can be supplied more surely to the exhaust gas purifying device  10 . 
         [0074]    Note that in the exhaust gas purifying system described above, if the operating state of the internal combustion engine  1  is a decelerating state, after the fuel added from the fuel adding valve  12  has reached the oxidation catalyst  11   e , the flowrate control valve  11   d  may be opened to a much larger opening degree, and an inflow quantity of the exhaust gas discharged from the internal combustion engine  1  into the oxidation catalyst  11   e  may thus be decreased to a greater degree. The operation being done so, the low-temperature exhaust gas in the decelerating state of the internal combustion engine  1  can be refrained from flowing into the oxidation catalyst  11   e , and the oxidation catalyst  11   e  can be also restrained from being cooled down. 
         [0075]      FIG. 3  shows an example of the exhaust gas purifying device temperature increasing routine in that case. A different point between the control in the present routine and the control in  FIG. 2  is that in the present routine, after judging in S 105  that the fuel reaches the oxidation catalyst  11   e , the operation proceeds to not S 106  but S 201 . It is judged in S 201  whether the internal combustion engine  1  is in the decelerating state or not. To be specific, an output of an unillustrated accelerator position sensor is read into the ECU  35 , and it may be judged whether an accelerator tread-on quantity obtained from this value is zero or not. A state where the accelerator is not trodden on may be defined as the decelerating state. 
         [0076]    When judging in S 201  that the internal combustion engine  1  is in the decelerating state, it is judged that if the flow rate control valve  11   d  is opened to the predetermined opening degree, and the exhaust gas from the internal combustion engine  1  is supplied to both of the internal pipe portion  11   b  and the external pipe portion  11   c  containing the oxidation catalyst  11   e  as explained in  FIG. 2 , the oxidation catalyst  11   e  is cooled down conversely. Hence, the operation proceeds to S 107 , wherein the flow rate control valve  11   d  is fully opened. Whereas if it is judged in S 201  that the internal combustion engine  1  is not in the deceleration state, as described in  FIG. 2 , the operation proceeds to S 106 . 
         [0077]    If done so, even in the case the internal combustion engine  1  is in the decelerating state and the reducing reaction occurs in the oxidation catalyst  11   e  due to the fuel added from the fuel adding valve  12 , it is feasible to restrain an occurrence of the situation that the oxidation catalyst  11   e  is cooled down by the low-temperature exhaust gas. As a result, the exhaust gas purifying device  10  can be warmed up more surely. 
         [0078]    It should be noted that in the first embodiment, when the internal combustion engine  1  is judged to be in the decelerating state in S 201 , if the flowrate control valve  11   d  is fully opened in S 107 , it follows that the low-temperature exhaust gas flows directly into the exhaust gas purifying device  10 . In this case also, however, the exhaust gas purifying device  10  has a larger thermal capacity than the oxidation catalyst  11   e  has, and hence such a problem, it is considered, is hard to occur that the exhaust gas purifying device  10  itself is cooled quickly down to the low temperature. 
         [0079]    Moreover, other than what has been discussed above, after finishing the warm-up of the internal combustion engine  1  in the first embodiment and when the exhaust gas purifying device temperature increasing routine is not executed, if the internal combustion engine  1  gets into the decelerating state, such control may also be conducted that the flow rate control valve  11   d  be fully opened. This control being thus conducted, after finishing the warm-up of the internal combustion engine  1 , it is possible to restrain the low-temperature exhaust gas from flowing into the oxidation catalyst  11   e  reaching the activation temperature or higher and also to restrain the oxidation catalyst  11   e  reaching at last the activation temperature or higher from being cooled down. 
       Second Embodiment 
       [0080]    Next, a second embodiment of the present invention will be described. The second embodiment will exemplify another configuration of the exhaust gas temperature increasing device  11  explained in  FIG. 1 . 
         [0081]      FIG. 4  is a view showing an outline of the configuration of the exhaust gas temperature increasing device  11  in the second embodiment. A first mode of the second embodiment is that as illustrated in  FIG. 4  (A), an exhaust gas purifying device  20  and an exhaust gas temperature increasing device  21  are substantially equalized in their diameters and are provided within a pipe having the same diameter. According to the first mode, the exhaust gas can be more smoothly flowed into the exhaust gas purifying device  20  without disturbing the flow of the exhaust gas discharged from the exhaust gas temperature increasing device  21 . Further, especially when an oxidation catalyst  21   e  is provided in an external pipe portion  21   c , the high-temperature exhaust gas discharged from the oxidation catalyst  21   e  can be more surely flowed into the outer peripheral portion of the exhaust gas purifying device  20 , with the result that the temperature of the exhaust gas purifying device  20  can be more certainly uniformly increased. Moreover, according to the first mode, a stepped portion  21   f  in  FIG. 4(A)  is not positioned between the exhaust gas temperature increasing device  21  and the exhaust gas purifying device  20 . It is therefore possible to restrain a large amount of heat from escaping outwardly of the exhaust pipe  5  because the exhaust gas discharged from the oxidation catalyst  21   e  flows against the stepped portion  21   f.    
         [0082]    Furthermore,  FIG. 4  (B) illustrates another mode of the second embodiment. In  FIG. 4  (B), the oxidation catalyst  21   e  is provided not in the external pipe portion  21   c  but in an internal pipe portion  21   b . With this arrangement, the oxidation catalyst  21   e  does not abut on the external portion of the exhaust pipe  5 , whereby the heat retaining property of the oxidation catalyst  21   e  can be more enhanced. 
         [0083]    Moreover, as shown in  FIG. 5 , such a mode may be taken that the exhaust gas purifying device  20  is partially inserted into the internal pipe portion  21   b .  FIG. 5(A)  shows a state where the flow rate control valve  21   d  is opened, while  FIG. 5(B)  shows a state where the flow rate control valve  21   d  is fully closed. According to the present mode, even when the exhaust gas purifying device  20  has a large capacity, the whole configuration including the exhaust gas temperature increasing device  21  and the exhaust gas purifying device  20  can be downsized, and the mountability on the vehicle can be improved. 
         [0084]    Further,  FIG. 6  illustrates still another mode of the second embodiment. In  FIG. 6(A) , an electro-thermic heater  21   g  is provided in the oxidation catalyst  21   e . Then, when heating up the exhaust gas purifying device  20 , to begin with, the electro-thermic heater  21   g  is electrified to emit the heat, thereby increasing the temperature of the oxidation catalyst  21   e  itself. When done so, it is feasible to increase the temperature of the oxidation catalyst  21   e  itself over the activation temperature more surely and to raise the temperature of the exhaust gas flowing into the exhaust gas purifying device  20  more certainly. 
         [0085]    Further, in  FIG. 6(B) , a glow plug  21   h  is provided upstream immediately of the oxidation catalyst  21   e . Then, when heating up the exhaust gas purifying device  20 , at first, the glow plug  21   h  is electrified to emit the heat, the temperature of the oxidation catalyst  21   e  itself is increased, and the temperature of the exhaust gas passing through the external pipe portion  21   c  is raised. Then, the fuel is added from the fuel adding valve  12 . With this operation, the temperature of the oxidation catalyst  21   e  itself can be increased over the activation temperature with more of the certainty, and the temperature of the exhaust gas discharged from the oxidation catalyst  21   e  can be further increased. Accordingly, the temperature of the exhaust gas flowing into the exhaust gas purifying device  20  can be raised more certainly. 
         [0086]    It is to be noted that the embodiments discussed above have exemplified the case of warming up the exhaust gas purifying device  10  or  20  when starting up the internal combustion engine  1 . In addition, the configurations and the control in the embodiments discussed above may be applied to a case of increasing the temperature of the NOx catalyst or of the filter in a SOx poisoning recovery process and in the PM regenerating process of the filter in the exhaust gas purifying device  10  or  20 . 
         [0087]    Further, the embodiments discussed above have exemplified the example of adding the fuel as the reducing agent from the fuel adding valve  12 , however, these embodiments may be applied to the exhaust gas purifying system that involves using urea water as the reducing agent. Moreover, these embodiments may also be applied to the exhaust gas purifying system of the internal combustion engine other than the diesel engine. In addition, these embodiments may also be applied to the exhaust gas purifying system adding the fuel as the reducing agent by executing the sub-injection such as VIGOM injection, POST injection, etc., from a fuel injection valve of the internal combustion engine. 
         [0088]    Moreover, the configuration of the exhaust gas purifying system according to the present invention is not limited to the configurations in the embodiments discussed above and can be modified as far as these modifications are within the range of the technical idea of the present invention. For example, full-close state of the flow rate control valve  11   d  in the embodiments discussed above does not necessarily mean completely closed state of valve. It can include the state that the flow rate control valve  11   d  is closed to a sufficiently small opening degree with which substantially an entire quantity of the exhaust gas from the internal combustion engine  1  can flow into the oxidation catalyst  11   e.    
       INDUSTRIAL APPLICABILITY 
       [0089]    According to the present invention, the temperature of the exhaust gas purifying device in the exhaust system of the internal combustion engine can be increased more efficiently or more surely with the much simpler configuration.