Patent Application
20120083966
The present invention relates to the field of internal combustion engines, and, more particularly, to internal combustion engines having exhaust aftertreatment devices.
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.
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.
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:
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.
Referring now to the drawings, and more particularly to
The engine system additionally includes a diesel particulate filter (DPF) 20 (labeled DPF in
Now, additionally referring to
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 ψAVG 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 ψAVG being set equal to (ψAVG+ψ)/2. Then, an end-of-service Life ratio Λ is set equal to the running average of time between regenerations ψAVG 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 ΛL. 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 ΛL, 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, ψAVG, ρ, τ, Λ.
Now, additionally referring to
Now, considering the first variation of method 200 in
If the end-of-service-life ratio Λ is less than or equal to the end-of-service-life ratio ΛL, 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 ΛL, 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 ρL is calculated by setting it equal to the maximum ash loading value μL depicted in step 212, which is a predetermined value, divided by the ash accumulation rate υ.
At step 214, the DPF service age ρ is compared to the maximum DPF service age ρL. If the DPF service age ρ is greater than or equal to the maximum DPF service age ρL, 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 ρL, 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 ψAVG, ρ, α, Λ, τ, μ, υ.
Now, discussing a second variation of method 200, and, more particularly, referring to
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
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.
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.
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.
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 ψAVG. 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.
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
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.
