Abstract:
Particulate material collected in a filter (PM) is burnt through a selected one of partial and perfect regenerating processes. The partial regenerating process starts, when an amount of PM is predicted to exceed a value between 2 to 10 g/l, and terminates, when the amount of PM is predicted to fall below a value between 1 to 4 g/l, whereby a part of PM is burned to an extent that incombustible ash contained in the filter (ASH) can not easily pass through the filter. The perfect regenerating process starts, when an amount of ASH is predicted to exceed a value between 0.05 to 0.25 g/l, and terminates, when the amount of PM is predicted to fall below 1 g/l, whereby a substantially entire part of PM is burnt to an extent that ASH can easily pass through the filter.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-5039 filed on Jan. 11, 2002. 
   FIELD OF THE INVENTION 
   The present invention relates to an exhaust gas filter regenerating apparatus for a filter that collects particulate material in an exhaust gas of an internal combustion engine and method of the same, in which burning of the particulate material is effectively controlled by selecting partial and perfect regenerating processes. 
   BACKGROUND OF THE INVENTION 
   A diesel particulate filter (DPF) is known as a filter that collects particulate material (PM) of an exhaust gas. Regenerating methods of burning the PM for continuous use of the DPF utilize heating with a burner or electric heater, fuel supply to the DPF having an oxidation catalyst by injection control, or the like. In a conventional method, the PM is fully burned every time the PM is deposited by a preset amount. The PM deposited in the DPF includes an impurity mainly composed of CaSO 4  that is a combination of Ca in engine oil and S contained in diesel oil. The impurity, so-called ash, is generated in a combustion chamber of an internal combustion engine or within the filter by reaction between Ca and SOx through burning of the PM during the filter regenerating. A particulate diameter of the ash is between 0.1 μm to several μm and less than an average diameter 30 μm of filter pores. As the burnable parts of the PM is burned during the filter regeneration process, the filter pores stuffed with the PM as shown  FIGS. 2A and 2B  are opened as shown in FIG.  2 C. The ash, which is incombustible, is thereby removed by passing through the filter pores with exhaust gas. 
   The regenerating method involves fuel consumption of the internal combustion engine through fuel supply to the filter, fuel supply to the burner, or fuel supply for generating electric power of the electric heater. Combustion speed of the PM has a tendency of decreasing with decrease of PM deposit amount. Combustion efficiency of the PM relative to the fuel consumption of the engine therefore decreases with the decrease of PM deposit amount during the regenerating process. In a conventional method, since the substantially entire amount of the PM deposited in the filter is burned every time once the PM deposit amount exceeds the preset amount, combustion efficiency on regenerating the filter is relatively low. This causes undesired increase of the fuel consumption in the regenerating method. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an exhaust gas filter regenerating apparatus that enables continuous use of a filter with less fuel consumption of an internal combustion engine. 
   To achieve the above object, regenerating a filter in a regenerating apparatus is executed as follows. Two parameters are detected. The first parameter has a value that is correlative with and predicts an amount of the collected particulate material. The second parameter has a value that is correlative with and predicts an amount of the incombustible impurity contained in the collected particulate material. Regenerating is executed by burning the collected particulate material and controlled by selectively performing either a partial or perfect process. In the partial regenerating process, a part of the collected particulate material is burnt to an extent that the impurity can not easily pass through the filter. In the perfect regenerating process, a substantially entire part of the collected particulate material is burnt to an extent that the impurity can easily pass through the filter. Here, the partial regenerating process starts when the value of the first parameter exceeds a first threshold and terminates when the value of the first parameter falls below a second threshold that is smaller than the first threshold. By contrast, the perfect regenerating process starts when the value of the second parameter meets a predetermined condition and terminates when the value of the first parameter falls below a third threshold that is smaller than the second threshold. 
   It is preferable that a value of the second threshold predicts that the collected particulate material remaining in the filter is an amount not less than 1 gram per liter of the filter and not more than 4 grams per liter of the filter. 
   It is preferable that a value of the third threshold predicts that the particulate material remaining in the filter is an amount not less than 0.05 gram per liter of the filter and not more than 0.25 grams per liter of the filter. 
   It is preferable that the second parameter is a cumulative driving mileage, a cumulative fuel injection amount, or a cumulative number of times of the partial regenerating processes. The cumulative driving mileage is reset at a time when the immediately previous perfect regenerating process terminates. The cumulative fuel injection amount is reset at a time when the immediately previous perfect regenerating process terminates. The cumulative number of times of the partial regenerating processes is reset at a time when the immediately previous perfect regenerating process terminates. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
       FIG. 1  is a graph showing partial and perfect regenerating process timing of diesel particulate filter (DPF) according to a first embodiment of the present invention; 
       FIGS. 2A  to  2 C are schematic sectional views of particulate material (PM) deposited in the DPF according to the first embodiment; 
       FIG. 3  is a schematic structural diagram of an exhaust gas filter regenerating apparatus according to the first embodiment; 
       FIG. 4  is a graph showing relationship between a PM deposit amount and PM combustion speed according to the first embodiment; 
       FIG. 5  is a flow diagram showing processing of exhaust gas filter regenerating process according to the first embodiment; 
       FIG. 6  is a flow diagram showing processing of exhaust gas filter regenerating process according to a second embodiment; 
       FIG. 7  is a flow diagram showing processing of exhaust gas filter regenerating process according to a third embodiment; and 
       FIG. 8  is a flow diagram showing processing of exhaust gas filter regenerating process according to a fourth embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   First Embodiment 
   A first embodiment is directed to a regenerating apparatus, shown in  FIG. 3 , for a diesel particulate filter (DPF)  26 . Structure of the regenerating apparatus will be explained hereunder. The regenerating apparatus is mounted on a vehicle that is driven by a diesel engine  38 . A suction pipe  44  is connected with a suction port (not shown) of the diesel engine  38 . An airflow meter  10  for detecting a suction flow amount is installed within the suction pipe  44 . A throttle valve  42  is installed on the downstream side of the airflow meter  10 , while driven by an electric motor  12  through a rotation axis  40  for adjusting the suction flow amount. 
   An exhaust pipe  30  is connected with an exhaust port (not shown) of the diesel engine  38 . The DPF  26 , formed of porous ceramics and coated with oxidation catalytic agent, is installed within the exhaust pipe  30 . 
   Detectors  24 ,  32  installed in the exhaust pipe  30  on both upstream and downstream sides of the DPF  26  are connected with a differential pressure sensor  34  for detecting differential pressure. A temperature sensor  22  is installed on the upstream side of the DPF  36  within the exhaust pipe  30 . 
   The suction pipe  44  and exhaust pipe  30  communicate with each other through an exhaust gas recirculation (ERG) pipe  20 . A part of the exhaust gas is thereby recirculated to the suction pipe  44 . An ERG valve  18  is installed within the ERG pipe  20  while driven by an electric motor  14  through a rotating axis  16  for adjusting an ERG flow amount. 
   An electronic control unit (ECU)  50  is equipped with ROM  58  for storing a program for regenerating an exhaust gas filter, CPU  60  for executing the program, RAM  56  and back-up RAM (B-RAM)  54  for storing data while executing the program, an input circuit  46 , and an output circuit  48 . These components are connected with each other through a bus  52 . The input circuit  46  is connected with the airflow meter  10 , the temperature sensor  22 , the differential pressure sensor  34  and other sensors while inputting respective signals to the CPU  60 . The output circuit  48  is connected with the electric motor  12  for the throttle valve  42 , the electric motor  14  for the ERG valve  18 , the injector  36  and others while supplying driving electric current to these devices based on control signals outputted by the CPU  60 . 
   The regenerating process of the regenerating apparatus will be explained hereunder. In the regenerating process, as main injection timing of the injector  36  is retarded in a combustion cycle, the fuel is injected to a cylinder from the injector  36  at a preset angular phase of a crank shaft (not shown) after the main injection. A part or all of the injected fuel after the main injection is exhausted, without being burned in the cylinder, into the exhaust pipe  30  to reach the DPF  26 . The unburned fuel that reaches the DPF  26  reacts with the oxidation catalyst to burn together with the PM deposited in the DPF  26 . The burned PM is exhausted downstream through the pore of the DPF  26  with the exhaust gas. 
   In the regenerating process, the unburned fuel that reaches the DPF  26  is also increased by decreasing the suction flow amount into the diesel engine  38 . Specifically, the suction flow amount is decreased by controlling to lessen an opening degree of the throttle valve  42  while the exhaust gas recirculation amount is decreased by controlling to lessen an opening degree of the ERG valve  18 . 
   Furthermore, in the regenerating process, heating with a burner or electric heater may be also adopted instead of the above fuel supply to the filter holding the oxidation catalyst. The temperature sensor  22  may be installed on the downstream side of the DPF  26  or a pair of the temperature sensors  22  may be installed on both upstream and downstream sides of the DPF  26  to accurately predict the temperature of the DPF  26 . 
   Referring to  FIG. 1 , partial and perfect regenerating processes will be explained below. The regenerating process is started when a PM deposit amount M per liter of the filter is assumed to exceed a threshold M 1  or when an ash deposit amount A per liter of the filter is assumed to exceed a threshold A 1 . 
   The threshold M 1  is desirably set to a value between 2 and 10 (2≦M 1 ≦10) grams per liter of the filter in consideration of combustion speed of the PM during the regenerating process as well as influence of fluid friction resistance on engine output due to the PM deposited in the DPF  26 . 
   If the threshold M 1  is set to a higher value, the engine output is reduced due to the excessive fluid friction resistance. On the other hand, if the threshold M 1  is set to a lower value, the combustion speed of the PM is decreased with decrease of PM deposit amount as shown in  FIG. 4  so that the combustion efficiency of the PM is lowered. 
   The threshold A 1  is desirably set to a value between 0.05 and 0.25 (0.05≦A 1 ≦0.25) gram per liter of the filter in consideration of fuel consumption for removing the PM almost perfectly from the DPF  26  as well as a contact area where a burnable part of the PM contacts the oxidation catalyst on the surface of the DPF  26 . 
   If the threshold A 1  is set to a lower value, the fuel consumption is excessively increased. On the other hand, if the threshold A 1  is set to a higher value, the contact area is excessively decreased so that the combustion efficiency is worsened. 
   Even in adopting the heating of the burner or electric heater for the regenerating process instead of the above method utilizing the oxidation catalyst, the threshold A 1  should not be set to an excessively higher value. When the threshold A 1  is set to the higher value, the burnable ratio of the PM deposited in the DPF  26  is excessively decreased. Decrease of the burnable ratio results in increase of the fuel consumption. 
   The regenerating process that is started when a PM deposit amount M per liter of the filter is assumed to exceed a threshold M 1  is terminated when the PM deposit amount M per liter of the filter is assumed to fall below a threshold M 2 . This regenerating process is defined as partial regenerating process. The threshold M 2  is desirably set to a value between 1 and 4 grams per liter of the filter (1≦M 2 ≦4) to terminate the process before the burnable part of the PM is not entirely burned. If the threshold M 2  is set to a lower value, the combustion efficiency of the PM is worsened due to the fuel consumption to be excessively increased as explained above. If the threshold M 2  is set to a higher value, frequency of the regenerating process is increased. This also results in increase of frequency of heating the exhaust pipe and others in addition to the DPF  26 . The fuel consumption thereby increases. 
   The regenerating process that is started when an ash deposit amount A per liter of the filter is assumed to exceed a threshold A 1  is terminated when the PM deposit amount M per liter of the filter is assumed to decrease to a threshold M 3  in which the ash can pass through the filter pores of the DPF  26 . This regenerating process is defined as perfect regenerating process. The threshold M 3  is desirably set to less than 1 (M 3 &lt;1) gram per liter of the filter. Through the perfect regenerating process, the filter pores stuffed with the PM are opened so that the ash is almost entirely removed by passing through the filter pore with the exhaust gas. 
   Referring to  FIG. 5 , processing routine of the regenerating process will be explained below. The routine is repeatedly executed every predetermined period. At step  100 , cumulative driving mileage L after the previous perfect regenerating process is detected. The mileage L is detected by reading a counter, stored in the RAM  56 , which is incremented according to the mileage and reset at the termination of the perfect regenerating process. The mileage L is used, as the second parameter (the first parameter is described later at step  105 ), for predicting the ash deposit amount A since the ash increases with mileage L. For instance, a threshold mileage L 1  of 1000 km is assumed to correspond to the threshold A 1 , e.g., 0.085 g/l, of the ash deposit where the perfect regenerating process should be started. 
   At step  105 , the PM deposit amount M is predicted by detecting, as the first parameter, exhaust temperature and pressure difference between the upstream and downstream sides of the DPF  26  through reading an exhaust temperature signal from the temperature sensor  22  and a pressure signal from the differential pressure sensor  34 . The PM deposit amount M may be predicted based on cumulative mileage, a cumulative fuel injection amount, or a cumulative suction flow amount of the airflow meter  10 . 
   At step  110 , whether the PM deposit amount M exceeds the threshold M 1  (2≦M 1 ≦10) is determined. Regardless of the determination at step  110 , whether the mileage L exceeds the threshold L 1  is determined at step  115  or step  140 . When the PM deposit amount M exceeds the threshold M 1  and the mileage L does not exceed the threshold L 1 , partial regenerating process starts at step  120 . When the mileage L exceeds the threshold L 1 , the ash deposit amount A is assumed to exceed the threshold A 1  so that perfect regenerating process starts at step  145  regardless of the determination whether the PM deposit amount M exceeds the threshold M 1 . When the PM deposit amount M and mileage L do not exceed the threshold M 1  and L 1  respectively, the processing returns to step  100  without any regenerating process. However, it may be differently programmed so that the perfect regenerating process can start, only when the PM deposit amount M exceeds the threshold M 1  and the mileage L exceeds the threshold L 1 . This means that step  140  is eliminated. Here, the threshold L 1  is set to, e.g., 1000 km corresponding to the threshold A 1  of the ash deposit amount. 
   In each of the partial and perfect regenerating processes at steps  120  and  145 , the regenerating process as already explained above is performed. 
   At each of steps  125  and  150 , the PM deposit amount M during the regenerating process is predicted by the same processing explained at step  105  based on the detection of the exhaust temperature and differential pressure between upstream and downstream sides of the DPF  26 . Each of the subsequent steps  130  and  155  is provided to determine the termination timing of the regenerating processes based on the PM deposit amount M predicted at step  125  or step  150 . At step  130  or step  155 , whether the PM deposit amount M exceeds the threshold M 2  (1≦M 2 ≦4) or M 3  (M 3 &lt;1) is determined. When the PM deposit amount M does not exceed the threshold M 2  or M 3 , the processing returns to step  125  or step  150 . When the PM deposit amount M exceeds the threshold M 2  or M 3 , the processing goes to step  135  or step  160  where the partial or perfect regenerating process is terminated. 
   Second Embodiment 
   A second embodiment utilizes a fuel injection amount as the second parameter for predicting the ash deposit amount A, while the first embodiment utilizes the driving mileage L. Referring to  FIG. 6 , the processing of the regenerating process is the same as that of  FIG. 5  of the first embodiment except for steps  200 ,  215  and  240 . 
   At step  200 , a cumulative fuel injection amount Q after the previous perfect regenerating process is detected. The fuel injection amount Q is detected by reading a counter, stored in the RAM  56 , which is incremented according to the fuel injection amount and reset at the termination of the perfect regenerating process. The fuel injection amount Q is used, as the second parameter, for predicting the ash deposit amount A since the ash increases with fuel injection amount Q. For instance, a threshold amount Q 1  of 60 liters is assumed to correspond to the threshold A 1 , e.g., 0.085 g/l, of the ash deposit where the perfect regenerating process should be started. 
   At steps  215  and  240 , whether the fuel injection amount Q exceeds the threshold Q 1  is determined. The other processing is the same as that of  FIG. 5  of the first embodiment as explained above. 
   Third Embodiment 
   A third embodiment utilizes the number C of partial regenerating process times after the previous perfect regenerating process as the second parameter for predicting the ash deposit amount A, while the first embodiment utilizes the driving mileage L. The other processing of the regenerating process is the substantially same as that of the first embodiment. 
   Referring to  FIG. 7 , at step  105 , a PM deposit amount M is predicted. At step  310 , whether the PM deposit amount M predicted at step  105  exceeds the threshold M 1  is determined. When the PM deposit amount M does not exceed the threshold M 1 , the processing returns to step  105 . When the PM deposit amount M exceeds the threshold M 1 , the processing proceeds to step  315  where whether the number C is equal to a threshold number C 1  is determined. 
   When the number C is less than the threshold number C 1 , the partial regeneration process is started at step  120 . After the partial regenerating process at steps  120 ,  125 ,  130 , and  135 , the number C is incremented by one at step  340 . 
   When the number C is equal to the threshold number C 1 , the perfect regeneration process is started at step  145 . After the perfect regenerating process at steps  145 ,  150 ,  155 , and  160 , the number C is reset to zero at step  365 . 
   The number C of the partial regenerating process times is used, as the second parameter, for predicting the ash deposit amount A since the ash increases with number C. For instance, a threshold number C 1  of 23 is assumed to correspond to the threshold A 1 , e.g., 0.085 g/l, of the ash deposit where the perfect regenerating process should be started. 
   Fourth Embodiment 
   A fourth embodiment simultaneously utilizes, as the second parameter for predicting the ash deposit amount A, the driving mileage L, the fuel injection amount Q, and the number C of partial regenerating process times after the previous perfect regenerating process. Referring to  FIG. 8 , the perfect regenerating process is started based on determination at step  415 . Namely, whether the parameter L exceeds its threshold value L 1  whether the parameter Q exceeds its threshold value Q 1 , or whether the parameter C is equal to the threshold value C 1  is determined. If at least one of the three determinations is affirmative, the processing proceeds to step  145  where the perfect regenerating process is started. By contrast, all of the three determinations are negative, the processing proceeds to step  120  where the partial regenerating process is started. Utilizing of the plurality of the second parameters enhances accuracy of predicting the ash deposit amount A and optimizes the timing of starting the perfect regenerating process. 
   Other Modification 
   After the iterative regenerating processes, an amount of the ash, the unburned part of the PM, remaining in the DPF  26  after the perfect regenerating process is gradually accumulated, while the burnable part of the PM is not accumulated. The differential pressure DP, after the perfect regenerating process, between the upstream and downstream sides of the DPF  26  is thereby correspondingly accumulated in comparison with the initial differential pressure DP 0  through a new filter. The differential pressure variation ΔP (DP−DP 0 ) can be used as the third parameter for predicting the ash deposit amount Ar remaining in the DPF  26  after the perfect regenerating process. Using the ash deposit amount Ar, unburned or burnable parts of the PM deposit amount M can be more accurately predicted, so that the threshold values such as M 1 , M 2  and M 3  are more properly adjusted.