Soot loading estimation during idle or low load

Abstract

System which features the following: an engine; a post-treatment system (100) which includes a particle filter (102); and a controller (120) that is trained: To receive engine operating conditions for the engine; to compare the engine operating conditions with one or more engine operating threshold values; to compare a time value since a last differential pressure soot loading estimation procedure with a predetermined time threshold; to lower a throughput threshold in response to the fact that the time value is greater than or equal to the predetermined time threshold; to compare a flow rate with the lower throughput threshold; and In response to the finding that the flow rate is greater than or equal to the lower flow threshold, to activate a differential pressure soot loading estimation procedure and to calculate a combined soot loading estimate using a differential pressure soot loading estimation procedure.

Description

TECHNICAL FIELD

[0001] The present application generally relates to the field of aftertreatment systems for internal combustion engines. BACKGROUND

[0002] In combustion engines, such as diesel engines, nitrogen oxide compounds (NO x compounds) and solid particles are released into the exhaust gas. To prevent NO x To reduce emissions, an SCR process can be used to reduce the NO x-compounds into more neutral compounds such as diatomic nitrogen, water, or carbon dioxide using a catalyst and a reducing agent. The catalyst may be contained within a catalyst chamber of an exhaust system, for example that of a vehicle or a power generation unit. A reducing agent, such as anhydrous ammonia, aqueous ammonia solution, or urea, is typically introduced into the exhaust stream upstream of the catalyst chamber. A diesel particulate filter (DPF) may be included in the internal combustion engine, either alone or within an SCR system, to remove particulate matter from the exhaust stream. In some cases, the DPF may be located upstream of the selective catalytic reduction system, downstream of the selective catalytic reduction system, or within the selective catalytic reduction system.To introduce the reducing agent for the SCR process into the exhaust gas stream, an SCR system can dose or otherwise introduce the reducing agent through a dosing module that vaporizes or sprays the reducing agent into an exhaust pipe of the exhaust system upstream of the catalyst chamber. The SCR system can have one or more sensors to monitor conditions within the exhaust system. EP 1 854 971 B1 discloses a method and apparatus for estimating the soot loading of a diesel particulate. DE 103 25 183 A1 describes a method and apparatus for performing a method for determining the loading state with an exhaust component of a component arranged in an exhaust region of an internal combustion engine. US 7 168 304 B2 discloses a method in which a fluid pressure in the vicinity of a filter is measured and compared with a predetermined value based on one or more operating parameters of an engine. SUMMARY

[0003] Implementations described herein relate to soot loading estimation during idle or low-load operating conditions. During idle or low-load operating conditions, pressure measurements for a delta pressure soot load estimation (DPSLE) method may be at low values, so small errors caused by pressure sensor devices and / or other system failures may affect the measurements. Accordingly, at such idle or low-load speeds, a controller for detecting soot enrichment on the aftertreatment components may ignore or not use such measurements for detecting soot enrichment due to reliability concerns.However, if an engine is running at low speed for an extended period of time, such as longer than 5 hours, 10 hours, 50 hours, or 100 hours, the ignored soot load estimate from the DPSLE method may result in an inaccurate estimate, missing soot buildup, such as in an aftertreatment system DPF, if only a mass-based soot load rate (MBSLR) estimation method is used. Accordingly, a control subroutine may regularly or periodically (e.g., every 8 hours, 10 hours, 20 hours, etc.) lower the flow threshold for using a DPSLE measurement and / or increase the engine speed and / or modify the exhaust gas recirculation (EGR) valve to increase exhaust flow through the aftertreatment system to a sufficiently high level to obtain a DPSLE measurement.In some implementations, the controller subroutine may modify fuel pressure, injection timing, variable turbine geometry, and / or intake or exhaust throttle to increase exhaust flow through the aftertreatment system. The DPSLE measurement may then be used as a known data point to update the combined soot load estimate (CSLE). In some implementations, the controller may also lower the flow threshold for the CSLE to utilize the DPSLE measurement.

[0004] One implementation relates to a system comprising an engine, an aftertreatment system having a particulate filter, and a controller. The controller is configured to receive engine operating conditions to the engine and compare the engine operating conditions to one or more engine operating thresholds. The controller is further configured to compare a time value since a last differential pressure soot loading estimation method to a predetermined time threshold. The controller is further configured to lower a flow rate threshold to a lower flow rate threshold in response to the time value being greater than or equal to the predetermined time threshold, compare a flow rate to the lower flow rate threshold, and activate a differential pressure soot loading estimation method in response to determining that the flow rate is greater than or equal to the lower flow rate threshold.The controller is further configured to calculate a combined soot loading estimate using a differential pressure soot loading estimate of the differential pressure soot loading estimation method in response to the lower flow threshold.

[0005] In some implementations, the engine operating conditions include an engine operating time, and the one or more engine operating thresholds include a predetermined engine operating time threshold. The predetermined engine operating time threshold may be at least 5 hours. In some implementations, the engine operating conditions include an engine speed per minute, and the one or more engine operating thresholds include a predetermined engine speed threshold (revolutions per minute). In some implementations, the controller may be further configured to increase a flow rate in the aftertreatment system in response to the time value being greater than or equal to the predetermined time threshold. In some implementations, increasing the flow rate in the aftertreatment system includes closing an exhaust gas recirculation valve and / or increasing an engine speed per minute.Increasing the engine speed per minute may occur during a power take-off regeneration process, which may include modifying the engine speed per minute to a first value for a first period of time and modifying the engine speed per minute to a second value for a second period of time after the first period of time. In still further implementations, the controller may be further configured to decrease the lower flow threshold over time. In still further implementations, the controller may be further configured to activate a particulate filter regeneration process based on the soot loading estimate of the differential pressure soot loading estimation process.

[0006] Another implementation relates to a method for interveningly increasing exhaust flow to update a differential pressure soot loading estimation method. The method includes comparing a time value since a last differential pressure soot loading estimation method with a predetermined time threshold and lowering a flow rate threshold to a lower flow rate threshold in response to the time value being greater than or equal to the predetermined time threshold.The method further includes increasing a flow rate in an aftertreatment system of the engine in response to the time value being greater than or equal to the predetermined time threshold, comparing the increased flow rate to the lower flow rate threshold, and activating a differential pressure soot loading estimation method in response to determining that the increased flow rate is greater than or equal to the flow rate threshold. The method further includes calculating a combined soot loading estimate using a differential pressure soot loading estimate of the differential pressure soot loading estimation method in response to the lower flow rate threshold.

[0007] In some implementations, decreasing the flow rate threshold is based on an engine operating time and / or an engine speed per minute. In some implementations, increasing the flow rate in the aftertreatment system comprises closing an exhaust gas recirculation valve and / or increasing an engine speed per minute. Increasing the engine speed per minute may occur during a power take-off regeneration process. In still other implementations, the method may further comprise activating a particulate filter regeneration process based on the combined soot loading estimate.

[0008] Yet another implementation relates to a device having a controller including a mass-based soot loading rate circuit, a differential pressure soot loading estimation circuit, a combined soot loading estimation circuit, and a low-flow soot treatment circuit. The mass-based soot loading rate circuit is configured to determine a mass-based soot loading estimate for a particulate filter of an aftertreatment system, and the differential pressure soot loading estimation circuit is configured to determine a differential pressure soot loading estimate for the particulate filter of the aftertreatment system. The combined soot loading estimation circuit is configured to determine a combined soot loading estimate for the particulate filter of the aftertreatment system based on the mass-based soot loading estimate and the differential pressure soot loading estimate.The low-flow soot treatment circuit is configured to compare a time value since a last differential pressure soot loading estimate to a predetermined time threshold. The low-flow soot treatment circuit is further configured to decrease a flow threshold to a lower flow threshold in response to the time value being greater than or equal to the predetermined time threshold, increase a flow rate in the engine aftertreatment system in response to the time value being greater than or equal to the predetermined time threshold, compare the increased flow rate to the lower flow threshold, and activate a differential pressure soot loading estimation method of the differential pressure soot loading estimation circuit in response to determining that the increased flow rate is greater than or equal to the lower flow threshold.The low flow soot treatment circuit is further configured to calculate a combined soot loading estimate using a differential pressure soot loading estimate of the differential pressure soot loading estimation method in response to the lower flow threshold.

[0009] In some implementations, lowering the flow threshold is based on an engine operating time and / or an engine speed per minute. In some implementations, increasing the flow rate in the aftertreatment system comprises closing an exhaust gas recirculation valve and / or increasing an engine speed per minute. Increasing the engine speed per minute may occur during a power take-off regeneration process. In still other implementations, the low-flow soot treatment circuit is further configured to regularly or periodically decrease the lower flow threshold. In some implementations, the predetermined time threshold is at least 5 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The details of one or more embodiments or implementations are set forth in the accompanying drawings and the description below. Further features, aspects, and advantages of the disclosure will become apparent from the description, drawings, and claims. In the drawings: Fig. 1 is a schematic block diagram of an exemplary aftertreatment system with a diesel particulate filter for an exhaust system; Fig. 2 is a block diagram of an exemplary controller including a mass-based soot loading rate circuit, a differential pressure soot loading estimation circuit, a combined soot loading estimation circuit, and a low-flow soot treatment circuit; Fig. 3 is a block diagram of an implementation of a method for activating an idle power or low-load soot treatment process; and Fig. 4 is a flow diagram of an implementation of an idle power or low load soot treatment method to activate a differential pressure soot loading estimation method.

[0011] It should be noted that some or all of the figures are schematic representations for illustrative purposes. The figures are provided for the purpose of illustrating one or more implementations with the explicit understanding that they will not be used to limit the scope or meaning of the claims. DETAILED DESCRIPTION

[0012] Below are more detailed descriptions of various concepts related to, and implementations of, methods, apparatus, and systems for estimating soot loading at idle or low engine speeds. The various concepts presented above and described in detail below can be implemented in one of numerous ways, as the described concepts are not limited to any particular implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes. I. Overview

[0013] In some engines, detecting the amount of soot enrichment at downstream aftertreatment components uses a differential pressure measurement of the pressure change across an aftertreatment component, such as by using an upstream and downstream pressure sensor. Such estimation of soot loading at the downstream aftertreatment components may be referred to as differential pressure soot loading estimation (DPS-LE). In some other implementations and / or in combination with DPSLE, detecting the amount of soot enrichment at downstream aftertreatment components uses a mass-based soot loading rate (MBSLR), which uses a model to estimate the amount of soot mass expelled downstream from the engine based on engine operating conditions.In some cases, the DPSLE and MB SLR can be combined in a CSLE, which is used during engine operation to estimate the soot loading on aftertreatment components, such as a particulate filter and in particular a diesel particulate filter (DPF).

[0014] In some implementations that use diesel engines, such as engines used as energy or other power sources and / or in vehicles with low loads or fluctuating duty cycles, the engine may operate at idle power or at low speeds with power take off (PTO) for extended periods. For example, in a diesel engine used as a power generator and / or for other purposes in a field application, such as oil and gas field operations, the engine may idle and / or operate at low load for extended periods. During such extended periods, soot and other particulate matter are continually generated and accumulate downstream of the engine in an aftertreatment system. In vehicles with low loads or fluctuating duty cycles, such as fire engines, garbage trucks, school buses, etc.The engine may also be operated at idle and / or low load for extended periods in such a way that soot and other particulate matter are continually generated and accumulate downstream of the engine in an aftertreatment system.

[0015] While DPSLE can be useful during higher-speed operation to estimate soot loading, pressure measurements during idle or low-speed operation can be so low that even small errors due to the pressure sensing device and / or other system faults can affect the measurements. Accordingly, for reliability reasons, a controller designed to detect soot buildup on the aftertreatment components at such idle or low speeds may ignore or not use such measurements to detect soot buildup. If an engine runs at low speed for an extended period of time, such as more than 10 hours, more than 50 hours, or more than 100 hours, ignoring DPSLE over that period can result in significant soot buildup, such as in a DPF of the aftertreatment system.

[0016] In implementations that also utilize the MB SLR soot loading estimate, the MB SLR may be sufficient to estimate soot loading when the DPSLE is inaccurate. However, because the MB SLR is a model-based estimated rate of soot enrichment based on engine operating conditions, even small errors in the estimate and / or changing engine operating conditions can affect the actual soot enrichment relative to the model-based estimate. Accordingly, over extended time, the MB SLR soot loading estimate may deviate from the actual soot loading to such an extent that significant soot enrichment may occur even if the MB SLR estimates a lower soot loading.

[0017] In some cases, when the engine is operated above idle speed and / or above low-speed power takeoff for such an extended period, the DPSLE may be read due to the increased flow through the aftertreatment system, resulting in more accurate pressure measurements. However, after such extended periods of operation at idle or low speeds, the soot accumulation may be sufficiently significant to result in a fault or error code being issued due to excessive soot accumulation. Accordingly, it may be advantageous to include a control subroutine and / or mechanism to update the CSLE and / or a sufficiently accurate DPSLE measurement during the extended period such that the soot loading can be more accurately estimated over the extended periods and / or a regeneration / desorption process can be triggered to reduce the soot loading.For example, a control subroutine may periodically (e.g., every 8 hours, 10 hours, 20 hours, etc.) lower a flow threshold for using the DPSLE soot loading estimate and / or increase exhaust flow through the aftertreatment system to a sufficiently high level to obtain a sufficiently accurate DPSLE measurement, such as by increasing engine speed and / or modifying the EGR valve. The DPSLE measurement may then be used for the combined soot loading estimate. Thus, the combined soot loading estimate may be more accurately estimated even during extended periods of idle operation and / or low-speed power takeoff by periodically obtaining DPSLE measurements.By increasing the accuracy of the soot loading estimation, the amount of soot loading can be controlled more effectively to reduce the likelihood of excessive soot accumulation and the triggering of trouble codes or faults when the engine is operated at higher than idle speed and / or low speed power takeoff. II. Overview of the aftertreatment system

[0018] Fig. 1 illustrates an aftertreatment system 100 with an exemplary reductant delivery system 110 for an exhaust system 190. The aftertreatment system 100 includes a particulate filter (specifically, a diesel particulate filter (DPF) 102), the reductant delivery system 110, a decomposition chamber or reactor 104, an SCR catalyst 106, and a sensor 150. The DPF 102 is configured to remove particulate matter, such as soot, from exhaust gas flowing in the exhaust system 190. The DPF 102 has an inlet through which the exhaust gas enters and an outlet through which the exhaust gas exits after particulate matter has been substantially filtered from the exhaust gas and / or particulate matter has been converted to carbon dioxide. The decomposition chamber 104 is designed to convert a reducing agent, such as urea, aqueous ammonia solution or AdBlue or diesel exhaust fluid (DEF) into ammonia.The decomposition chamber 104 includes a reductant delivery system 110 with a dosing module 112 configured to dose the reductant into the decomposition chamber 104. In some implementations, the reductant is injected upstream of the SCR catalyst 106. The reductant droplets then undergo the processes of evaporation, thermolysis, and hydrolysis to form gaseous ammonia within the exhaust system 190. The decomposition chamber 104 includes an inlet in fluid communication with the DPF 102 to receive the exhaust gas containing NO. x -emissions, as well as an outlet for the exhaust gas, NO x emissions, ammonia and / or remaining reductant to flow to the SCR catalyst 106.

[0019] The decomposition chamber 104 includes the dosing module 112 attached to the decomposition chamber 104 such that the dosing module 112 can dose the reductant into the exhaust gases flowing in the exhaust system 190. The dosing module 112 can include an isolator 114 placed between a portion of the dosing module 112 and the portion of the decomposition chamber 104 where the dosing module 112 is mounted. The dosing module 112 is fluidly coupled to one or more reductant sources 116. In some implementations, a pump 118 can be used to pressurize the reductant source 116 for supply to the dosing module 112.

[0020] The dosing module 112 and the pump 118 are also electrically or communicatively coupled to a controller 120. The controller 120 is configured to control the dosing module 112 to dose reducing agent into the decomposition chamber 104. The controller 120 may also be configured to control the pump 118. The controller 120 may include a microprocessor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), etc., or combinations thereof. The controller 120 may include a memory, including, but not limited to, an electronic, optical, magnetic, or other storage or transmission device capable of providing program instructions to a processor, ASIC, FPGA, etc.The memory may comprise a memory chip, an electrically erasable programmable read-only memory (EEPROM), an erasable programmable read-only memory (EPROM), flash memory, or other suitable memory from which the controller 120 may read instructions. The instructions may comprise code from any suitable programming language. In certain implementations, the controller 120 is structured to perform certain operations, such as those described herein with respect to the . Fig. 3 through 5. In certain implementations, controller 120 represents part of a processing subsystem that includes one or more computing devices with storage, processing, and communication hardware. Controller 120 may be a single device or a distributed device, and the functions of controller 120 may be performed by hardware and / or as computer instructions on a non-transitory computer-readable storage medium.

[0021] In certain implementations, the controller 120 includes one or more circuits structured to functionally perform the operations of the controller 120. In certain implementations, the controller 120 may be configured to perform the operations related to the Fig. 3-5 may include an MBSLR circuit, a DPSLE circuit, a combined soot load estimation circuit, and a low-throughput soot treatment circuit. The description herein, including the circuits, emphasizes the structural independence of the aspects of the controller 120 and illustrates a possible grouping of operations and responsibilities of the controller 120. Other groupings that perform similar overall operations are to be considered within the scope of the present application. Circuits may be implemented in hardware and / or as computer instructions on a non-transitory computer-readable data storage medium, and circuits may be distributed across various hardware or computer-based components. More detailed descriptions of specific embodiments of the controller operations are included in the section related to Fig. 3 to 5.

[0022] Example and non-limiting circuit implementation elements include sensors that provide any value specified herein, sensors that provide any value that is a precursor to a value specified herein, datalink and / or network hardware including communication chips, oscillating crystals, communication links, cables, twisted pair wiring, coaxial wiring, shielded wiring, transmitters, receivers and / or transceivers, logic circuits, hard-wired logic circuits, reconfigurable logic circuits in a specific, non-volatile state configured according to the circuit specification, actuators including at least one electrical, hydraulic or pneumatic actuator, a solenoid, an operational amplifier, analog control elements (springs, filters, integrators, adders, dividers,amplification elements) and / or digital controls.,

[0023] The SCR catalyst 106 is designed to reduce NO x emissions by initiating a NO x reduction process between the ammonia and the NO x of the exhaust gas into diatomic nitrogen, water, and / or carbon dioxide. The SCR catalyst 106 has an inlet in fluid communication with the decomposition chamber 104, from which exhaust gas and reductant are received, and an outlet in fluid communication with one end of the exhaust system 190.

[0024] The exhaust system 190 may further include a diesel oxidation catalyst (DOC) in fluid communication with the exhaust system 190 (e.g., downstream of the SCR catalyst 106 or upstream of the DPF 102) to oxidize hydrocarbons and carbon monoxide in the exhaust gas.

[0025] In some implementations, the DPF 102 may be positioned downstream of the decomposition chamber or reactor tube 104. For example, the DPF 102 and the SCR catalyst 106 may be combined into a single unit, such as an SDPF. In some implementations, the dosing module 112 may instead be positioned downstream of a turbocharger or upstream of a turbocharger.

[0026] The sensor 150 may be coupled to the exhaust system 190 to detect a condition of the exhaust flow through the exhaust system 190. In some implementations, the sensor 150 may have a region disposed within the exhaust system 190, e.g., a tip of the sensor 150 may extend into a region of the exhaust system 190.

[0027] In other implementations, the sensor 150 may receive exhaust gas through another conduit, such as a sample tube extending from the exhaust system 190. While the sensor 150 is illustrated as being positioned downstream of the SCR catalyst 106, it should be understood that the sensor 150 may be positioned at other locations in the exhaust system 190, including upstream of the DPF 102, within the DPF 102, between the DPF 102 and the decomposition chamber 104, within the decomposition chamber 104, between the decomposition chamber 104 and the SCR catalyst 106, within the SCR catalyst 106, or downstream of the SCR catalyst 106. Additionally, two or more sensors 150 may be used to detect a condition of the exhaust gas, such as, for example, exhaust gas decomposition. B. two, three, four, five or six sensors 150, each sensor 150 being arranged at one of the aforementioned positions of the exhaust system 190. III. Implementation of soot loading estimation at idle or low load

[0028] Fig. Figure 2 illustrates an implementation of a controller 200 such that the controller 120 of Fig. 1 includes an MBSLR circuit 210, a DPSLE circuit 220, a CSLE circuit 230, and a low flow soot treatment circuit 240. In some implementations, the controller 200 may be configured to perform the tasks of the circuits 210, 220, 230, and 240 described herein. The MBSLR circuit 210 is configured to evaluate one or more engine operating condition parameters that indicate characteristic values ​​of engine operating conditions, such as mass fuel flow, engine speed, mass air intake flow, an engine operating time value, etc. The MBSLR circuit 210 may also evaluate a parameter that indicates one or more engine operating condition parameters that indicate characteristic values ​​of engine operating conditions from a lookup table, such as one or more lookup tables stored in a data memory.The MBSLR circuit 210 generates a soot loading estimate based on the one or more parameters for the engine operating conditions. For example, the MBSLR circuit 210 may receive the one or more parameters for the engine operating conditions and determine an estimated soot loading using an equation or a lookup table, such as a mass transport equation for calculating a mass of soot emitted by the engine into the exhaust system based on the operating conditions, and / or retrieving a value from a lookup table using the one or more parameters as index values.

[0029] The DPSLE circuit 220 is configured to evaluate a parameter that indicates a characteristic value of a pressure change along a component of the aftertreatment system, such as the DPF 102 of Fig. 1. This means that pressure sensors can be located upstream and downstream of the aftertreatment system component. A measurement of the pressure upstream and downstream of the aftertreatment system component can be taken, and the difference between the two values ​​(e.g., P strömungsaufwärts -P strömungsabwärts ) can be calculated as the differential pressure, ΔP, across the aftertreatment system components. The DPSLE circuit 220 calculates a soot loading estimate based on the differential pressure value and, in some implementations, additional parameters (e.g., exhaust temperature, exhaust mass flow rate, DPF flow rate, etc.).

[0030] The soot loading estimate from the MBSLR circuit 210 and the DFPSLE circuit 220 is received by the CSLE circuit 230 and used to calculate a CSLE value. In some implementations, the CSLE circuit 230 receives a parameter indicating a characteristic value of a DPF flow rate, such as an ACMS rate, which indicates the volume of exhaust gases flowing through the DPF per second. The CSLE circuit 230 may be configured to compare the DPF flow rate to a predetermined threshold, such as 0.38 ACMS. If the DPF flow rate is below the predetermined threshold, the soot loading estimate from the DPSLE circuit 220 may be less accurate due to the low flow rate. Accordingly, in some implementations, the DPSLE circuit 220 may be disabled while the DPF throughput is below the threshold.In further implementations, the soot loading estimate from the DPSLE circuit 220 may be ignored by the CSLE circuit 230.

[0031] During extended periods of idle or low-speed power takeoff, the CSLE circuit 230 may ignore the soot loading estimate from the DPSLE circuit 220 for extended periods or not utilize this value. This results in the combined soot loading estimate being calculated solely from the soot loading estimate from the MB SLR circuit 210, the accuracy of which may progressively deteriorate over time. However, as time progresses and the accuracy of the soot loading estimate from the MB SLR circuit 210 also deteriorates, it may be preferable to use a less accurate soot loading estimate from the DPSLE circuit 220 rather than solely the soot loading estimate from the MB SLR circuit 210.In some cases, if after sustained idle or low-speed power take-off, the engine is running such that the DPF flow rate increases above the threshold so that the soot loading estimate from the DPSLE circuit 220 can be used, the actual soot loading may be high due to accumulated errors from the soot loading estimate of the MBSLR circuit 210, which may result in the need for maintenance or other intervention to correct the high soot loading.

[0032] The low-flow soot treatment circuit 240 is configured to evaluate a parameter indicating a time at which the DPF flow rate last exceeded the predetermined threshold and compare the time to a time threshold, such as 8 hours, 10 hours, 20 hours, 100 hours, or any other time threshold. The low-flow soot treatment circuit 240 may start a timer when the DPF flow rate last exceeded the predetermined DPF flow rate threshold and periodically compare the timer value to the time threshold. If the DPF flow rate increases above the predetermined DPF flow rate threshold before the timer value exceeds the time threshold, the low-flow soot treatment circuit resets the timer.In some implementations, if the timer value exceeds the time threshold, the low flow soot treatment circuit 240 outputs a new, lower predetermined DPF flow threshold.

[0033] For example, if the predetermined DPF flow rate threshold is 0.38 ACMS, and if the time at which the DPF flow rate last exceeded the predetermined threshold is 11 hours compared to a time threshold of 10 hours, the low flow soot treatment circuit 240 outputs a new, lower predetermined DPF flow rate threshold, such as 0.25 ACMS, 0.2 ACMS, etc., to the CSLE circuit 230. Thus, if the DPF flow rate is below 0.38 ACMS but above 0.25 ACMS or 0.2 ACMS, the CSLE circuit 230 may use the soot loading estimate from the DPSLE circuit 220 to generate the combined soot loading estimate by the CSLE circuit 230, which may correct any accumulated errors that are a result of the soot loading estimate of the MBSLR circuit 210 over the extended period.The extension allows the soot loading estimate from DPSLE circuitry 220 to be "trusted" at lower ACMS after extended periods, where the soot loading estimate from MBSLR circuitry 210 alone may have lower accuracy for the combined soot loading estimate. If the DPF flow rate is still below the lower predetermined threshold, DPSLE circuitry 220 remains in a standby mode and is not utilized by CSLE circuitry 230. In some cases, if DPSLE circuitry 220 is "reliable," then the value output by DPSLE circuitry 220 to CSLE circuitry 230 may be assigned a higher weight than normal. In some other cases, if the DPF flow rate is measured for a total calibratable time, such as 3 minutes, 5 minutes, 10 minutes, 15 minutes, 30 minutes, etc., is above the lower predetermined threshold and the DPSLE circuit 220 provides values ​​to the CSLE circuit 230 for the calibratable time, the lower predetermined threshold may be increased back to the predetermined threshold, and the process may be repeated. During the calibratable time, the lower predetermined threshold is used even if the DPF flow rate exceeds the higher predetermined threshold. In some implementations, the total calibratable time may comprise the accumulation of shorter individual periods when the DPF flow rate is above the lower predetermined threshold.

[0034] In some implementations, the low-flow soot treatment circuit 240 may decrease the predetermined DPF flow rate threshold over time. For example, the low-flow soot treatment circuit 240 may decrease the predetermined DPF flow rate threshold in periodic increments, such as 0.01 ACMS per hour, 0.015 ACMS per hour, etc. Accordingly, the low-flow soot treatment circuit 240 may slowly decrease the predetermined DPF flow rate threshold over time until the DPF flow rate exceeds the threshold to use the soot loading estimate of the DPSLE circuit 220.

[0035] In some cases, desorption events occur periodically, such as every 10 hours. However, in some cases, desorption events may not generate enough flow for the DPF flow rate to exceed the predetermined threshold. In some implementations, the low-flow soot treatment circuit 240 may modify one or more engine parameters to increase the DPF flow rate. For example, during desorption events, such as hydrocarbon desorption events, the low-flow soot treatment circuit 240 may modify one or more engine parameters and / or apply different engine parameters during the desorption event such that the DPF flow rate exceeds the predetermined threshold. The one or more engine parameters may include engine speed, EGR amount, etc.

[0036] In some implementations, the modified one or more engine parameters may be applied for the duration of the desorption event. In other implementations, the modified one or more engine parameters may be applied for an initial period, with the previous engine parameters then being applied for the remainder of the desorption event, such as a dual-speed event.During a dual-speed event, the engine parameters may initially be set to the modified engine parameters to operate the engine at a higher speed for a short period of time, and then the previous engine speed may be used to release the hydrocarbons for the remainder of the desorption event duration, limiting the impact on fuel economy and avoiding the risk of releasing hydrocarbons too quickly, while also increasing the DPF flow rate above the lowered predetermined threshold. The additional flow rate generated by the modified one or more engine parameters may not be sufficient to exceed the predetermined DPF flow rate threshold, but it may be adjusted to be sufficient to exceed the lowered DPF flow rate.For some implementations that utilize hydrocarbon desorption events, the engine parameters can be retrieved from a table of values, such as Table 1 below:.

[0037] Thus, during the desorption event, the low flow soot treatment circuit 240 may use the engine speed parameters of Table 1 to increase the engine speed to increase the DPF flow sufficiently to exceed the threshold of the CSLE circuit 230.

[0038] In some further implementations, the CSLE circuit 230 may assign a weighting factor to the soot loading estimate of the DPSLE circuit 220 based on the difference between the threshold value and the measured DPF flow rate (e.g., the weighting factor may be assigned: 0.1 ACMS with a weight of 0 and 0.38 ACMS with a weight of 1.0, and the values ​​between 0.1 ACMS and 0.38 ACMS may be weighted proportionally). This means that when the DPF flow rate decreases below the weight of the predetermined threshold value of 0.38 ACMS toward the lower limit of 0.1 ACMS, the weight of the soot loading estimate may be used by the CSLE circuit 230. The weighting factor may be used as a reliability factor value that indicates the reliability of the estimate of the DPSLE circuit 220.For example, the CSLE circuit 230 may use only a percentage of the estimate from the DPSLE circuit 220, proportional to the reliability indicated by the reliability factor value. If the reliability factor indicates that the reliability of the estimate from the DPSLE circuit 220 is very low, the CSLE circuit 230 may proportionally use much more or all of the estimate from the MBSLR circuit 210 relative to the estimate from the DPSLE-SLR circuit 210 to determine the combined soot loading estimate. If the reliability factor indicates that the reliability of the estimate from the DPSLE circuit 220 is very high, the CSLE circuit 230 may proportionally use much more or all of the estimate from the DPSLE circuit 220 with the estimate from the MBSLR circuit 210 to determine the combined soot loading estimate.

[0039] Fig. Figure 3 shows a block diagram of an implementation of a method 300 for activating an idle power or low-load soot treatment method. The method 300 includes the steps of receiving engine operating conditions (block 310), comparing the engine operating conditions to one or more thresholds (320), and activating an idle power or low-load soot treatment method (block 330).

[0040] At block 310, a controller, such as controller 120, 200, receives the engine operating conditions (block 310). The engine operating conditions may be one or more parameters evaluated by the controller and / or a circuit of the controller. For example, the engine operating conditions may include a flow rate, such as a DPF flow rate, an engine speed, an air intake mass flow, an engine operating time, and / or other parameters indicative of the engine operating conditions.

[0041] Method 300 includes comparing the engine operating conditions to one or more thresholds (block 320), such as engine operating thresholds. In some implementations, a parameter indicative of a characteristic value of a DPF flow rate, such as an actual cubic meter per second (ACMS) rate, which indicates the volume of exhaust gases flowing through the DPF per second, is compared to a predetermined threshold, such as 0.38 ACMS. In some implementations, a parameter indicative of a characteristic value of an engine speed is compared to a predetermined engine speed threshold, such as 800 rpm, 750 rpm, 700 rpm, etc. In some implementations, a parameter indicative of a characteristic value of an air intake mass flow is compared to a predetermined threshold.In some implementations, a parameter indicating a characteristic value of an engine operating time is compared to a predetermined engine operating time threshold, such as 5 hours, 10 hours, 20 hours, 50 hours, 100 hours, etc. Still other engine operating conditions may be compared to one or more thresholds.

[0042] In some implementations, if the DPF flow rate is below the corresponding predetermined threshold, the engine will then run in idle or low load mode such that the DPSLE soot loading estimate is not updated. In further implementations, the determination that the DPSLE soot loading estimate is not updated may be based on additional engine operating parameters, either in addition to or instead of the DPF flow rate. For example, in some implementations, the determination may also be based on one or more of the conditions that the engine operating time exceeds a threshold, that the engine speed is below a threshold, and / or that the air intake mass flow is below a threshold.In still further implementations, the determination may be based on the engine operating conditions used meeting the threshold criteria for a predetermined period of time, such as one minute, 15 minutes, 30 minutes, one hour, two hours, etc. The predetermined period of time may be set such that the determination of the idle or low-load condition does not occur during temporary or minimal periods of operation at idle power or low load.

[0043] If the DPSLE soot loading estimate is not updated, method 300 then includes activating an idle or low-load soot treatment method (block 330). The idle or low-load soot treatment method may include activating the low-flow soot treatment circuit 240 of Fig. 2 to output a new, lower predetermined DPF flow rate threshold to the CSLE circuit 230 and / or to modify one or more engine parameters.

[0044] Fig. 4 illustrates a flowchart of an implementation of an idle or low-load soot treatment method 400 for decreasing a flow threshold and / or increasing an exhaust flow in an aftertreatment system to activate a differential pressure soot loading estimation method. The method 400 begins with activation (block 410). In some implementations, the idle or low-load soot treatment method 400 is responsive to activating an idle or low-load soot treatment method (block 330) of Fig. 3.

[0045] Method 400 includes comparing the time elapsed since the last execution of the DPSLE method to a predetermined time threshold (block 412). In some implementations, a time for the last used soot loading estimate from the DPSLE circuit 220 may be stored in a memory of the controller. The stored time may be compared to a current engine operating time to determine the amount of time since the last execution of the DPSLE method. The amount of time since the last execution of the DPSLE method is compared to the time threshold, such as 5 hours, 8 hours, 10 hours, 20 hours, 50 hours, 100 hours, etc. If the amount of time since the last execution of the DPSLE method is not greater than the time threshold, the method returns to block 412 to again compare the amount of time to the time threshold.In some implementations, a delay time may be included to avoid a continuous comparison of the duration with the time threshold and delay the subsequent comparison. The delay time may be, for example, 30 minutes, 45 minutes, one hour, two hours, five hours, etc.

[0046] In some implementations, when the idle power or low-load soot treatment process is started or activated (block 410), a timer may be started as an approximate value for the amount of time since the last DPSLE process and compared to the time threshold. Thus, the time for the last DPSLE process does not need to be stored, but may be approximated by the timer value. In some implementations, if a DPF flow rate increases above a predetermined DPF flow rate threshold before the timer value exceeds the time threshold, the timer and / or the timer value may be reset.

[0047] If the time since the last DPSLE procedure was executed is greater than the threshold, method 400 may include modifying a flow threshold for the DPSLE procedure (block 414). Modifying the flow threshold includes modifying the predetermined DPF flow threshold, such as 0.38 ACMS, to a new, lower predetermined DPF flow threshold, such as 0.25 ACMS, 0.2 ACMS, etc.

[0048] In some implementations, method 400 may include increasing a flow rate in an aftertreatment system (block 416). Increasing the flow rate in the aftertreatment system may include closing an EGR valve (either partially or fully), increasing the engine speed, etc. Increasing the flow rate or increasing the engine speed may occur when the engine is idling and not during power takeoff. In some implementations, increasing a flow rate in the aftertreatment system may occur during a triggering or desorption event. Increasing the flow rate in the aftertreatment system may include operating the engine at a first speed for a first period of time during a desorption event and a second speed for a second period of time during a desorption event. Table 1 provides some example values ​​for operating the engine at the first speed (e.g.,850 rpm) for the first period (0 seconds to 120 seconds) and the second speed (e.g., 760 rpm, 800 rpm, 850 rpm) for the second period (130 seconds to 6000 seconds, or any other final value for the desorption event). In some implementations, the first speed may be lower than the second speed.

[0049] In some implementations, method 400 may include waiting for a dwell time (block 418) to allow the increased flow rate to propagate through the aftertreatment system and stabilize. The dwell time may be, for example, one minute, two minutes, five minutes, etc.

[0050] A flow rate indicative parameter is evaluated (block 420) and compared to the lower flow rate threshold (block 422). The flow rate indicative parameter may be evaluated from a flow sensor in the aftertreatment system and / or by a feedforward estimate of the flow rate. If the value of the flow rate parameter is below the lowered predetermined threshold, the method may return to evaluate a new value of the flow rate parameter (block 420), e.g., remain in standby mode, and / or return to change the flow rate threshold to a new, lower threshold (block 418). In implementations that change the flow rate threshold to a new, lower threshold (block 418), method 400 may decrease the predetermined threshold, such as 0.01 ACMS per hour, 0.015 ACMS per hour, etc., after method 400 is activated.

[0051] If the value of the flow parameter is above the lowered predetermined threshold, such as 0.25 ACMS or 0.2 ACMS, the DPSLE may be considered reliable. Method 400 includes evaluating a value of a differential pressure parameter (block 424). Evaluating the differential pressure parameter includes evaluating a parameter that indicates a characteristic value of a pressure change in a component of the aftertreatment system, such as the DPF 102 of Fig. 1. This means that pressure sensors can be located upstream and downstream of the aftertreatment system component. A measurement of the pressure upstream and downstream of the aftertreatment system component can be taken and the difference between the two values ​​(e.g., P strömungsaufwärts -P strömungsabwärts ) can be calculated as the differential pressure, ΔP, along the aftertreatment system component.

[0052] A DPSLE process is activated (block 426) to calculate a soot loading estimate. The DPSLE circuit 220 of Fig. 2, for example, calculates a soot loading estimate based on the differential pressure value and, in some implementations, other parameters (e.g. exhaust gas temperature, exhaust gas mass flow rate, etc.).

[0053] The soot loading estimate from the DPSLE method can then be combined with the soot loading estimate from the MB SLR method (such as that implemented by the MBSLR circuit 210) to calculate a combined soot loading estimate (CSLE). In some implementations, a weighting factor can be applied to the soot loading estimate of the DPSLE method based on the difference between the threshold and the measured DPF flow rate (e.g., the weighting factor can be assigned: 0.1 ACMS with a weight of 0 and 0.38 ACMS with a weight of 1.0, and the values ​​between 0.1 ACMS and 0.38 ACMS can be weighted proportionally). This means that as the DPF flow rate decreases below the weighting of the predetermined threshold of 0.38 ACMS towards the lower limit of 0.1 ACMS, the weighting of the soot loading estimate from the DPSLE method can be lowered when used for the CSLE value.The weighting factor can be used as a reliability factor value that indicates the reliability of the DPSLE estimate. For example, the combined soot loading estimate may use only a percentage of the DPSLE estimate, proportional to the reliability indicated by the reliability factor value. If the reliability factor indicates that the reliability of the DPSLE estimate is very low, the combined soot loading estimate may use proportionally much more or the entire MBSLR estimate relative to the DPSLE estimate to determine the combined soot loading estimate. If the reliability factor indicates that the reliability of the DPSLE estimate is very high, the combined soot loading estimate may use proportionally much more or the entire DPSLE estimate relative to the MBSLR estimate to determine the combined soot loading estimate.

[0054] In some implementations, if the throughput parameter is above the lower predetermined threshold for an entire calibratable time, such as 3 minutes, 5 minutes, 10 minutes, 15 minutes, 30 minutes, etc., and the DPSLE method continues to return values ​​for the CSLE value for the calibratable time, the lower throughput threshold may be increased back to the higher predetermined threshold, and method 400 may be repeated. During the calibratable time, the lower throughput threshold is used even if the throughput parameter exceeds the higher predetermined threshold.In some implementations, the total calibratable time may comprise the accumulation of shorter individual time periods when the throughput parameter is above the lower predetermined threshold, even if there is an intermediate period during which the throughput parameter is below the lower throughput threshold.

[0055] In some implementations, method 400 includes activating a power take-off regeneration procedure (428). Based on the CSLE value calculated using the soot loading estimate of the DPSLE procedure, a determination is made that the soot loading may be too high for the DPF, and a power take-off regeneration procedure may be initiated to regenerate the DPF.

[0056] In further implementations, method 400 may set a flag for a regeneration process (block 430). For example, if further conditional parameters are not currently met, the flag may be set such that a regeneration process occurs when the conditional parameters are met. In some implementations, the regeneration process may be initiated without the further conditional parameters being met.

[0057] In some implementations, method 400 may not increase the flow rate in the aftertreatment system (block 416), but may only modify the flow rate threshold for the DPSLE process (block 414). In other implementations, method 400 may not modify the flow rate threshold for the DPSLE process (block 414), but may only increase the flow rate in the aftertreatment system (block 416).

[0058] The term "controller" includes all types of devices, apparatus, and machines for processing data, including, for example, a programmable processor, a computer, a system on a chip (SOC), or multiple thereof, a portion of a programmed processor, or combinations of the foregoing. The device may include dedicated logic circuitry, such as an FPGA or ASIC. The device may also include, in addition to hardware, code that creates an execution environment for the computer program in question, such as code representing processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more thereof.The device and the execution environment can implement various different computing model infrastructures, such as distributed computing and grid computing infrastructures.

[0059] A computer program (also known as a program, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and it can be deployed in any form, for example, as a stand-alone program or as a circuit, component, subroutine, object, or other unit suitable for use in a computing environment. A computer program may, but does not have to, correspond to a file in a file system. A program may be stored in a section of a file containing other programs or data (for example, one or more scripts stored in a markup language document), in a single dedicated file for the program in question, or in multiple coordinated files (for example, files storing one or more circuits, subroutines, or pieces of code).

[0060] Although this document contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular implementations. Certain features described in this specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination.In addition, although the above features may be described as functioning in certain combinations and may initially be claimed as such, in some cases one or more features from a claimed combination may be singled out from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0061] Similarly, while operations are illustrated in the drawings in a particular order, this should not be understood to require that these operations be performed in that particular order or in sequential order, or that all of the illustrated operations be performed to achieve desirable results. Under certain circumstances, the separation of various system components in the implementations described above may not be understood to require such separation in all implementations, and it should be understood that the described components and systems may generally be integrated into a single product or may be packaged in multiple products embodied on tangible media.

[0062] As used herein, the terms "approximately," "substantially," and similar terms are intended to have a broad meaning consistent with conventional and accepted usage by those skilled in the art to which this disclosure belongs. It will be apparent to those skilled in the art reading this disclosure that these terms are intended to permit description of certain described and claimed features without limiting the scope of those features to the precise numerical ranges provided. Accordingly, these terms are to be construed to indicate that insignificant or insignificant modifications or variations to the described and claimed subject matter are considered within the scope of the invention as recited in the appended claims.In addition, it is stated that limitations of the claims, in the event that the term "means" is not used therein, are not to be interpreted as constituting "means plus function" limitations under the United States patent laws.

[0063] The terms "coupled," "connected," and the like, as used herein, mean the direct or indirect connection of two components to one another. This connection may be stationary (e.g., permanent) or movable (e.g., removable or detachable). This connection may be achieved by the two components, or the two components and any other intermediate components, being integrally formed with one another as a single unitary body, or by the two components, or the two components and any other intermediate components, being attached to one another.

[0064] The terms "fluidly coupled" or "in fluid communication," and the like, as used herein, mean that the two components or objects have a path formed between the two components or objects in which a fluid, such as water, air, gaseous reductant, gaseous ammonia, etc., can flow, either with or without intervening components or objects. Examples of fluid couplings or configurations for enabling fluid communication may include tubes, channels, or any other suitable components for enabling the flow of a fluid from one component to another.

[0065] It is important to note that the construction and arrangement of the system shown in the various example implementations are merely illustrative and not restrictive. It is intended that all changes and modifications that fall within the spirit and / or scope of the described implementations are protected. It is understood that some features are not necessary, and implementations lacking the various features are considered within the scope of the application, which scope is defined by the following claims. In reading the claims, it is intended that the use of words such as "a," "an," "at least one," or "at least one region / portion / part," as well as their declinations, is not intended to limit the claim to only one subject matter, unless expressly stated otherwise in the claim.Where the terms “at least one area” / “at least one area / portion / part” and / or “one area” / “one area / portion / part” are used, the subject matter may include one area / portion / part and / or the entire subject matter, unless expressly stated otherwise.

Claims

[1] System which has the following: an engine; an aftertreatment system (100) comprising a particulate filter (102); and a controller (120) which is designed: to receive engine operating conditions to the engine; to compare the engine operating conditions with one or more engine operating thresholds; compare a time value since a last differential pressure soot loading estimation procedure with a predetermined time threshold; lower a throughput threshold to a lower throughput threshold in response to the time value being greater than or equal to the predetermined time threshold; compare a flow rate with the lower flow threshold; and in response to determining that the flow rate is greater than or equal to the lower flow rate threshold, activate a differential pressure soot loading estimation method and calculate a combined soot loading estimate using a differential pressure soot loading estimate of the differential pressure soot loading estimation method. [2] The system of claim 1, wherein the engine operating conditions comprise an engine operating time, and wherein the one or more engine operating thresholds comprise a predetermined engine operating time threshold. [3] The system of claim 2, wherein the predetermined engine operating time threshold is at least 5 hours. [4] The system of claim 1, wherein the engine operating conditions comprise an engine speed per minute, and wherein the one or more engine operating thresholds comprise a predetermined engine speed per minute threshold. [5] The system of claim 1, wherein the controller (120) is further configured to: increase a flow rate in the aftertreatment system (100) in response to the time value being greater than or equal to the predetermined time threshold. [6] The system of claim 5, wherein increasing the flow rate in the aftertreatment system (100) comprises closing an exhaust gas recirculation valve. [7] The system of claim 5, wherein increasing the flow rate in the aftertreatment system (100) comprises increasing an engine speed per minute. [8] The system of claim 7, wherein increasing the engine speed per minute occurs during a power take-off regeneration process. [9] The system of claim 8, wherein the power take-off regeneration method comprises modifying the engine speed per minute to a first value for a first period of time and modifying the engine speed per minute to a second value for a second period of time after the first period of time. [10] The system of claim 1, wherein the controller (120) is further configured to decrease the lower throughput threshold over time. [11] The system of claim 1, wherein the controller (120) is further configured to: to activate a regeneration process for the particulate filter (102) based on a soot loading estimate of the differential pressure soot loading estimation process. [12] A method for interveningly increasing exhaust flow to update a differential pressure soot loading estimation method, comprising the following steps: Comparing a time value since a last differential pressure soot loading estimation procedure with a predetermined time threshold; lowering a throughput threshold to a lower throughput threshold in response to the time value being greater than or equal to the predetermined time threshold; Increasing a flow rate in an aftertreatment system (100) of the engine in response to the time value being greater than or equal to the predetermined time threshold; Comparing the increased flow rate with the lower flow threshold; and Activating a differential pressure soot loading estimation method and calculating a combined soot loading estimate using a differential pressure soot loading estimate of the differential pressure soot loading estimation method in response to determining that the increased flow rate is greater than or equal to the flow rate threshold. [13] The method of claim 12, wherein lowering the flow threshold is based on an engine operating time. [14] The method of claim 12, wherein lowering the flow threshold is based on an engine speed per minute. [15] The method of claim 12, wherein increasing the flow rate in the aftertreatment system (100) comprises closing an exhaust gas recirculation valve. [16] The method of claim 12, wherein increasing the flow rate in the aftertreatment system (100) comprises increasing an engine speed per minute. [17] The method of claim 16, wherein increasing the engine speed per minute occurs during a power take-off regeneration process. [18] The method of claim 12, further comprising the step of: Activating a regeneration process for a particulate filter (102) based on the combined soot loading estimate. [19] Device comprising a controller (120; 200) comprising: a mass-based soot loading rate circuit (210) configured to determine a mass-based soot loading estimate for a particulate filter (102) of an aftertreatment system (100); a differential pressure soot loading estimation circuit (220) configured to determine a differential pressure soot loading estimate for the particulate filter (102) of the aftertreatment system (100); a combined soot loading estimation circuit (230) configured to determine a combined soot loading estimate for the particulate filter (102) of the aftertreatment system (100) based on the mass-based soot loading estimate and the differential pressure soot loading estimate; and a low-flow soot treatment circuit (240) configured to: compare a time value since a last differential pressure soot loading estimate with a predetermined time threshold; lower a throughput threshold to a lower throughput threshold in response to the time value being greater than or equal to the predetermined time threshold; increasing a flow rate in the engine aftertreatment system (100) in response to the time value being greater than or equal to the predetermined time threshold; compare the increased flow rate with the lower flow threshold; and in response to determining that the increased flow rate is greater than or equal to the lower flow rate threshold, activate a differential pressure soot loading estimation method of the differential pressure soot loading estimation circuit (220) and calculate a combined soot loading estimate using a differential pressure soot loading estimate of the differential pressure soot loading estimation method. [20] The apparatus of claim 19, wherein lowering the flow threshold is based on an engine operating time. [21] The apparatus of claim 19, wherein lowering the flow threshold is based on an engine speed per minute. [22] The apparatus of claim 19, wherein increasing the flow rate in the aftertreatment system (100) comprises closing an exhaust gas recirculation valve. [23] The apparatus of claim 19, wherein increasing the flow rate in the aftertreatment system (100) comprises increasing an engine speed per minute during a power take-off regeneration process. [24] The apparatus of claim 19, wherein the low flow soot treatment circuit (240) is further configured to periodically decrease the lower flow threshold. [25] The apparatus of claim 19, wherein the predetermined time threshold is at least 5 hours.

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