FIELD OF THE INVENTION 
       [0001]    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 
       [0002]    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. 
         [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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 
       [0008]    In one form, the invention includes a particulate filter ash loading prediction method including the steps of determining a maximum average lifetime for the particulate filter; performing a calculation of a running average of time between regenerations of the particulate filter; calculating an end-of-service-life ratio of the particulate filter dependent upon the maximum average lifetime and the running average; and comparing the end-of-service-life ratio to a predetermined minimum end-of-service-life ratio. If the end-of-service-life ratio is equal to or less than the minimum end-of-service-life ratio then indicating that at least one of service and replacement of the particulate filter is needed due to ash loading. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    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: 
           [0010]      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; 
           [0011]      FIG. 2  depicts a schematical representation of a method utilized in the vehicle of  FIG. 1 ; and 
           [0012]      FIGS. 3A ,  3 B and  3 C are schematical representations of two variations of another embodiment of the method utilized in the vehicle of  FIG. 1 . 
       
    
    
       [0013]    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 
       [0014]    Referring now to the drawings, and more particularly to  FIG. 1 , there is shown a vehicle  10 , which may be an agricultural work vehicle, a forestry work vehicle or a construction type vehicle utilizing an engine system that includes an air intake  12 , an engine  14 , a fuel supply system  16  (labeled FUEL in  FIG. 1 ), and an exhaust system  18  (labeled EXHAUST in  FIG. 1 ). 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 combustion chamber that receives air for combustion from air intake  12  and fuel from fuel supply system  16 . The products of combustion pass through exhaust system  18 . 
         [0015]    The engine system additionally includes a diesel particulate filter (DPF)  20  (labeled DPF in  FIG. 1 ) and a catalyst  22  (labeled CAT in  FIG. 1 ). 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 catalyst  22  and is exhausted in the form of gas flow  30  to the environment. DPF  20  and catalyst  22  may be combined into one unit or catalyst  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 . 
         [0016]    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. Method  100  includes a step  102  in which the DPF service age ρ, as well as the time between regenerations ψ are separately integrated by a process of integration or summing. This summing of the DPF service age ρ and this step also keeps track of the time between regenerations ψ. At step  104 , a decision is made as to whether DPF  20  requires a regeneration. This may be decided upon the delta pressure across DPF  20  as sensed by sensors  34  and  36  under the control of controller  32  and upon other portions of method  100 , such as the compensation for the ash loading that is occurring in DPF  20 . With the ash loading prediction being made by the present invention, then the contribution of backpressure in DPF  20  that is attributed to the particulate matter that is to be cleaned from DPF  20  can be accurately assessed to determine if it is time for a regeneration of DPF  20  to take place. If no regeneration is needed, step  104  proceeds back to step  102  but the time continues to be tracked for the DPF service age ρ and the time between regenerations ψ. If a DPF regeneration needs to take place as decided at step  104 , method  100  proceeds to step  106  in which a DPF regeneration cycle is initiated and takes place. 
         [0017]    A predetermined minimum DPF age τ, schematically shown as step  108  is used in step  110  to compare to the DPF service age ρ to see if ρ is greater than or equal to τ. If the integrated DPF service age ρ is not greater than or equal to the minimum DPF age τ, then method  100  resets the time between regenerations ψ to be equal to zero, at step  112  so that it will then start re-accumulating time at step  102 . This portion of method of  100  ensures that at least a minimum age for DPF  20  is realized before establishing a service life for DPF  20 . In the event that the DPF service age ρ exceeds or is equal to the minimum DPF age τ, method  100  proceeds to step  114  to determine if a maximum average time α has been set. If the answer is no, then the maximum average time is set to the most recent time between regenerations ψ and ψ AVG  is also set equal to ψ, at step  116 . If the maximum average time α has been previously set, then method  100  proceeds from step  114  to step  118  in which the running average of the time between regeneration is calculated by the equation of ψ AVG  being set equal to (ψ AVG +ψ)/2. Then, an end-of-service Life ratio Λ is set equal to the running average of time between regenerations ψ AVG  divided by the maximum average time α and the time between regenerations ψ is set to zero, at step  120 . Method  100  then proceeds to step  122 , in which it is determined whether the end-of-service life ratio Λ is less than or equal to the end-of-service life ratio maximum Λ L . If the answer is no, then method  100  proceeds to step  102 . If the end-of-service life ratio Λ is less than or equal to end-of-service life ratio maximum Λ L , then method  100  proceeds to step  124  in which an indication is made that service or the replacement of the DPF  20  is necessary. The indication may be in the form of an illuminated warning light on a console supervised by an operator or some other form of communication of the information to the operator of vehicle  10  or to maintenance personnel. Additionally, at step  124 , when the service or replacement of DPF  20  takes place, variables are set to zero such as ψ, ψ AVG , ρ, τ, Λ. 
         [0018]    Now, additionally referring to  FIGS. 3A ,  3 B, and  3 C, there is shown another embodiment of the ash loading prediction method described above. Method  200  has two variations, which are further explained in  FIGS. 3B and 3C . The variations of method  200  are to be understood to be illustrated in the differences in  FIGS. 3B and 3C . The first variation of method  200  utilizes  FIGS. 3A and 3B  and the second variation of method  200  utilizes  FIGS. 3A and 3C . Steps that are similar between method  100  and  200  retain the same numbers from method  100  and perform the functions as discussed above. 
         [0019]    Now, considering the first variation of method  200  in  FIG. 3A , if DPF  20  regeneration takes place at step  106 , then, at step  202 , it is determined whether the ash accumulation rate υ is greater than zero. If the ash accumulation rate υ is not greater than zero, then method  200  proceeds to step  110 . If the ash accumulation rate υ is greater than zero at step  202 , then method  200  proceeds to step  214  and bypasses several steps, since the ash accumulation rate υ has been established. 
         [0020]    If the end-of-service-life ratio Λ is less than or equal to the end-of-service-life ratio Λ L , then method  200  proceeds to step  206 . In the event that end-of-service-life ratio Λ is not equal to or less than the end-of-service-life ratio maximum Λ L , then method  200  proceeds to step  102 . At step  206 , DPF  20  ash loading value μ is set by utilizing the service life ratio versus DPF ash loading table depicted in step  204  to thereby determine the ash loading value μ. Once the ash loading value μ is established, method  200  proceeds to step  208  in which the ash accumulation rate υ is calculated by setting it equal to the ash loading value μ divided by the service age ρ value. At step  210 , the maximum DPF service age ρ L  is calculated by setting it equal to the maximum ash loading value μ L  depicted in step  212 , which is a predetermined value, divided by the ash accumulation rate υ. 
         [0021]    At step  214 , the DPF service age ρ is compared to the maximum DPF service age ρ L . If the DPF service age ρ is greater than or equal to the maximum DPF service age ρ L , then method  200  proceeds to step  216 . If the DPF service age ρ is not greater than or equal to the maximum DPF service age ρ L , then method  200  proceeds to step  102 . At step  214 , an indication is provided to the operator of vehicle  10  or maintenance personnel of vehicle  10  that servicing and/or replacement of DPF  20  is necessary. The indication may be in the form of an illuminated warning light on a console supervised by the operator or some other form of communication of the information to the operator of vehicle  10  or to the maintenance personnel. Additionally, at step  216 , when the service or replacement of DPF  20  takes place, variables are set to zero, such as ψ AVG , ρ, α, Λ, τ, μ, υ. 
         [0022]    Now, discussing a second variation of method  200 , and, more particularly, referring to  FIGS. 3A and 3C , steps  218  and  220  have been incorporated and steps  210  and  214  are eliminated. Step  218  is undertaken upon the completion of step  208  or upon the affirmative answer of the test at step  202 . At step  218 , the DPF  20  ash loading value μ is calculated by setting it equal to the DPF service age ρ times the ash accumulation rate υ. Then, at step  220 , the comparison is undertaken to see if the ash loading value μ is greater than or equal to maximum ash loading value μ L  obtained as a predetermined value, as illustrated in step  212 . If the ash loading value μ is greater than or equal to the maximum ash loading value μ L , then method  200  proceeds to step  216  in which the DPF  20  is serviced and/or replaced. If the DPF ash loading value μ is not greater than or equal to the maximum ash loading value μ L , then method  200  proceeds back to step  102 . 
         [0023]    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 DPF  20  soot loading. 
         [0024]    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. 
         [0025]    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. 
         [0026]    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. 
         [0027]    Methods  100  and  200  deal with ash that is accumulated in DPF  20  with time, and recognizes the normalized delta pressure readings will tend to increase, leading to more frequent regenerations. The increase in the number of regenerations can be tied in direct proportion to the overall average time between regenerations. The maximum average time α is calculated early on in engine and aftertreatment service life. Although it can be calculated from the first several samples of time between regenerations, waiting for DPF age ρ to pass a minimum DPF age τ allows there to be ample time for the maximum average time α to be established and thereby avoid a possible over calculation of the maximum average time between regenerations. 
         [0028]    After the maximum average time α is calculated, it will be continuously referenced to calculate the end-of-service life ratio Λ using the ongoing calculation of the running average of time between regenerations ψ AVG . As DPF  20  loads with ash and the regeneration frequency increases, Λ decreases from 1.0. However, as ash accumulates in DPF  20 , the normalized and non-normalized delta pressure will trend at higher levels for the same soot loading than if there was no ash present in DPF  20 . 
         [0029]    From experimental testing, it has been found that the end-of-service life ratio Λ can be used as an input to an ash loading table to determine the ash loading value μ. The ash loading value μ is then used to calculate the ash accumulation rate υ. Either the DPF service age ρ is used as the test, as in  FIG. 3B , or the ash loading value μ is used as the test, as in  FIG. 3C  to determine if it is time to service and/or replace DPF  20 , at step  216 . 
         [0030]    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. 
         [0031]    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.
A particulate filter ash loading prediction method including the steps of determining a maximum average lifetime for the particulate filter; performing a calculation of a running average of time between regenerations of the particulate filter; calculating an end-of-service-life ratio of the particulate filter dependent upon the maximum average lifetime and the running average; and comparing the end-of-service-life ratio to a predetermined minimum end-of-service-life ratio. If the end-of-service-life ratio is equal to or less than the minimum end-of-service-life ratio then indicating that at least one of service and replacement of the particulate filter is needed due to ash loading.