Abstract:
A particulate filter (PF) ash loading prediction method includes the steps of: regenerating the PF using a first soot loading prediction model or a second soot loading prediction model; determining whether the regeneration of the PF was initiated by the first soot loading prediction model or the second soot loading prediction model; incrementing a first counter associated with the first soot loading prediction model or a second counter associated with the second soot loading prediction model, dependent on the determining step; comparing a ratio of the first counter and the second counter; and establishing whether the PF requires servicing, dependent on the ratio.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of internal combustion engines, and, more particularly, to internal combustion engines having exhaust aftertreatment devices. 
     BACKGROUND OF THE INVENTION 
     Internal combustion engines come in a number of forms, the most common of which are spark-ignited gasoline fueled engines and compression-ignition, diesel-fueled engines. The compression-ignition, or diesel-type engine is used in many commercial and industrial power applications because its durability and fuel economy are superior to the spark-ignited gasoline-fueled engines. A diesel engine utilizes the heat of the compression of the intake air, into which a timed and metered quantity of fuel is injected, to produce combustion. The nature of the diesel engine cycle is that it has a variable air-fuel ratio that can, under partial power conditions, rise to levels significantly above stoichiometric. This results in enhanced fuel economy since only the quantity of fuel needed for a particular power level is supplied to the engine. 
     One of the issues with a diesel-type engine is the impact on emissions. In addition to the generation of carbon monoxide and nitrous oxide, there is a generation of particulates in the form of soot. A number of approaches are employed to reduce particulates while, at the same time, reducing oxides of nitrogen to ever more stringent levels as mandated by government regulations. Stoichiometric engines have been proposed to achieve this balance since they enable the use of an automotive type catalyst to reduce oxides of nitrogen. By operating the engine at or near stoichiometric conditions, a three-way catalyst may be utilized. However, operation in this manner causes a substantial increase in diesel particulates. Accordingly, a particulate filter (PF) in the form of a diesel particulate filter (DPF) must be employed to filter out the particulates, but the generation of particulates in a significant amount require that frequent regeneration of the filters, through temporary heating or other means, is necessary to remove the collected particulate matter. A wall-flow DPF will often remove 85% or more of the soot during operation. Cleaning the DPF includes utilizing a method to burn off the accumulated particulate either through the use of a catalyst or through an active technology, such as a fuel-burner, which heats the DPF to a level in which the soot will combust. This may be accomplished by an engine modification which causes the exhaust gasses to rise to the appropriate temperature. This, or other methods, known as filter regeneration, is utilized repeatedly over the life of the filter. One item that limits the life of the DPF is an accumulation of ash therein that will cause the filter to require replacement or some other servicing, such as a cleaning method, to remove the accumulated ash. The accumulated ash causes a reduction in the efficiency of the DPF and causes increased back pressure in the exhaust system of the diesel engine system. 
     U.S. Patent Application Pub. No. US 2007/0251214 discloses an apparatus for detecting a state of a DPF with a differential pressure sensor. An electronic control unit estimates an amount of ash remaining in the DPF based on the output of the differential pressure sensor immediately after the regeneration process. Alternatively, the residue ash amount may be calculated based on the difference between a ratio of the variation rate of the input manifold pressure with the variation rate of the differential pressure immediately after the regeneration process and an equivalent ratio regarding a thoroughly new or almost new diesel particulate filter. The residue ash amount is calculated every time a regeneration process is carried out and stored in memory. This method is problematic since the backpressure assessment after regeneration can be misleading if the soot has not been entirely removed and since the backpressure due to the ash accumulation measured after each regeneration can vary leading to misleading assumptions about the ash content. 
     U.S. Pat. No. 6,622,480 discloses a DPF unit and regeneration control method that adjusts the start timing of a regeneration operation. The method includes an estimate of the ash accumulated quantity that is in the exhaust gas and accumulated in the filter and the correction of the exhaust pressure judgment value for judging the regeneration operation start based on the ash accumulated estimation value. The ash quantity is determined from the quantity of lubricant oil consumed according to the engine operation state. The effective accumulation in the filter with ash is reflected in the judgment of regeneration start timing because the exhaust pressure judgment value to be used for judging the regeneration operation start is corrected with the ash accumulation estimation value. The use of oil consumption is problematic since the lubricant oil may be consumed in ways other than being combusted. Further, even if the oil is not combusted, it is not necessarily passed through the DPF. 
     It is also possible that direct-injected gasoline engines may require the use of a PF in the future, as a result of ever increasing governmental emissions standards. 
     What is needed in the art is a system that maximizes the life of a PF, such as a DPF, while ensuring that the regeneration process is done in an efficient, economical manner. 
     SUMMARY 
     The invention in one form is directed to a PF ash loading prediction method, including the steps of: regenerating the PF using a first soot loading prediction model or a second soot loading prediction model; determining whether the regeneration of the PF was initiated by the first soot loading prediction model or the second soot loading prediction model; incrementing a first counter associated with the first soot loading prediction model or a second counter associated with the second soot loading prediction model, dependent on the determining step; comparing a ratio of the first counter and the second counter; and establishing whether the PF requires servicing, dependent on the ratio. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a schematic drawing of a vehicle with an internal combustion engine employing an embodiment of an ash loading prediction method of the present invention; and 
         FIG. 2  depicts a schematical representation of the method utilized in the vehicle of  FIG. 1 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one embodiment of the invention and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION 
     Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a vehicle  10 , which may be a work vehicle such as an agricultural work vehicle, construction type vehicle or forestry type vehicle, utilizing an engine system that includes an air intake  12 , an engine  14 , a fuel supply system  16  (labeled FUEL), and an exhaust system  18  (labeled EXHAUST). Engine  14  has at least one piston reciprocating within an engine block that is connected to a crankshaft for producing a rotary output (not shown). Each piston is movable within a variable volume cylinder (not shown). The products of combustion pass through exhaust system  18 . 
     The engine system additionally includes a PF in the form of DPF  20  and a catalyst (CAT)  22 . Although the embodiment of the invention illustrated in the drawings and described herein is with reference to a diesel engine having a DPF, it is understood that the present invention can likewise apply to other types of engines using a PF, such as a direct-injected gasoline engine, etc. An air intake flow  24  passes into engine  14  for the purposes of combustion, having an exhaust flow  26  that passes through DPF  20  and a gas flow  28  that continues through CAT  22  and is exhausted in the form of gas flow  30  to the environment. DPF  20  and CAT  22  may be combined into one unit, or CAT  22  may be positioned at a different location or omitted from the engine system. A controller  32  interacts with sensors  34  and  36  as well as fuel supply system  16  to control the flow of fuel and to sense the pressure drop across DPF  20 . DPF  20  may be regenerated as directed by controller  32  with input of the sensors  34  and  36 , each of which provide pressure readings so that the pressure drop across DPF  20  can be calculated by controller  32  based on the difference in pressure measurements between sensors  34  and  36 . Controller  32  provides input to fuel supply system  16 , which may cause engine  14  to change the exhaust temperature flowing through exhaust system  18  to DPF  20 , causing a regeneration of DPF  20 . 
     DPF  20  may be in the form of a wall-flow filter that traps soot with a very high efficiency, even above 90%. When the soot cake layer has been established within DPF  20 , filling the inlet channel walls, the pressure increases across DPF  20  and a soot trapping efficiency of higher than 99% may be achieved. It is common to measure a pressure drop across 
     DPF  20  through the use of a delta pressure sensor, which may include two sensors, such as those illustrated in  FIG. 1  as sensors  34  and  36 . The readings from sensors  34  and  36  are used to predict soot loading of DPF  20 . These predictions can be made with models, such as those developed by Konstandopoulos, et al., described in SAE standard 2002-01-1015. A high filtration efficiency DPF  20  also traps ash, which can come from high ash lube oil, excessive oil consumption, and high ash fuels, such as biodiesel. As ash gradually accumulates in DPF  20 , the DPF  20  delta pressure signal received by controller  32  at a given soot level will be higher. This behavior is due to ash occupying space in the inlet channels of DPF  20 , leaving less surface/volume for soot distribution. 
     Now, additionally referring to  FIG. 2 , there is shown an ash loading prediction method  100  utilized within controller  32 , which may be interconnected to other sensors and control systems. Controller  32  may have other functions unrelated or indirectly related to the functions of method  100  of the present invention. 
     During operation, a loop state occurs in which it is determined if DPF  20  requires regeneration as a result of soot buildup (decision block  102  and line  104 ). With the present invention, the regeneration of DPF  20  may be initiated by one of two different soot loading prediction models. Using two different soot loading prediction models, any discrepancies between the models can be attributed to an ash loading increase within DPF  20 . The first soot loading prediction model “A” utilizes a pressure differential across DPF  20 , as measured by sensors  34  and  36 . The pressure signals are used to determine soot loading with the Konstandopoulos, et al. derived equations as described above, and further described in SAE standard 2002-01-1015. 
     The second soot loading prediction model “B” may be any one of a number of soot loading prediction models, not based on a measured pressure differential across DPF  20 . For example, the second soot loading prediction model “B” may be a time based counter which triggers a regeneration of DPF  20  based upon hours of engine operation; an open loop soot loading prediction model using lookup tables based on engine parameters such as engine speed, engine load, etc; a soot loading prediction model using multiple input linear regression equations with a physics and/or chemistry based model; or a linearly regressed multiple input soot loading model using six sigma practices. Other soot loading models which are not based on a measured pressure differential across DPF  20  may also be possible. 
     When a regeneration of DPF  20  occurs (line  106 ), then a determination is made as to whether first soot loading prediction model “A” or second soot loading prediction model “B” initiated the regeneration of DPF  20  (block  108 ). If the first soot loading prediction model “A” initiated the regeneration, then a counter α associated with the first soot loading prediction model “A” is incremented by a value of one ( 1 ). Likewise, if the second soot loading prediction model “B” initiated the regeneration, then a counter β associated with the second soot loading prediction model “B” is incremented by a value of one (1). 
     At block  110 , the ratio β/α is calculated using the values of the counters β and α. As ash loading within DPF  20  increases over time, more regenerations of DPF  20  occur based on the delta pressure based soot loading, causing the delta pressure regeneration counter α to increase in the denominator, and the β/α ratio to further decrease below one (1). 
     At decision block  112 , the value of the ratio β/α is compared with the value of a predefined β/α ratio limit (i.e., threshold value). If the actual ratio β/α is greater than or equal to the value of the β/α ratio limit, then servicing of the DPF  20  is not required and the method logic returns via lines  114  and  116  to the input of decision block  102 . On the other hand, if the actual ratio β/α is less than the value of the β/α ratio limit, then servicing of the DPF  20  is required (block  118 ). After servicing, which may include cleaning or replacement of DPF  20 , then the counters β and α are reset to zero (0), and the ratio β/α is reset to zero (0) (block  120 ). The method logic then returns via line  116  to the input of decision block  102 . 
     An optional method of using the ratio β/α to determine whether servicing of DPF  20  is required is illustrated along line  122  from block  110 . More particularly, the ratio β/α may be used as an input value to a lookup table, for example a two-dimensional lookup table, to determine an end of service life for DPF  20  (block  124 ). The ratio β/α lies along the horizontal or ordinate axis of the lookup table, and the percent of service life (or end of service life) lies along the vertical or abscissa axis of the lookup table. If the ratio β/α does not correspond to an end of service life condition (decision block  126 ), then the method logic returns via line  128  to the input of decision block  102 . On the other hand, if the ratio β/α does correspond to and end of service life condition, then the method logic proceeds via line  130  to blocks  118  and  120 , as described above. 
     Overall, ash accumulation is generally a slow process. Total exhaust system back pressure due to ash starts to become noticeable above 2,500 hours of engine operation for greater than 130 kilowatt applications, and above 1,500 hours of operation for less than 130 kilowatt applications. However, in addition to the effect on engine performance due to higher back pressure, the delta pressure sensor readings increase as a result of the ash loading. Without any compensation for ash loading, the time interval between regenerations starts to decrease since the aftertreatment control system will determine that a DPF  20  regeneration needs to occur based on delta pressure readings. 
     It is known that ash loading of DPF  20  will cause higher delta pressure readings across DPF  20  to become progressively higher with soot loading and that such effects cannot be remedied by merely averaging. Also, ash accumulation can take a significant amount of engine operation time to show substantial effects on DPF delta pressure signals and exhaust back pressures. 
     Advantageously, the present invention provides a statistically based ash model to monitor and verify the ash prediction that is not based on operation hours or fuel consumption history, as utilized in prior art systems. Further, the method is also capable of flagging excessive oil consumption or poor fuel quality that results in excessive loading of DPF  20 . Additionally, the present invention reduces the number of DPF regenerations when the DPF  20  is approaching the end-of-service life. The method can also generate an input for a monitor after determining that an ash service warning or engine degradation is occurring or may occur. Yet further, the present invention can compensate for the use of biodiesel, which has a tendency to create additional ash over petroleum based diesel. 
     While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.