DE112015000334T5 - Strategy for detecting the permeability of a diesel exhaust fluid filter and machine using it - Google Patents

Abstract

A reductant dosing system (20) for an exhaust aftertreatment system (16) of a diesel engine (15) includes a reductant tank (21) having an intake volume (25) separated by a sump filter from an exhaust volume (26). A filter permeability state is detected by the electronic controller (23) using a filter state algorithm (55) that compares fluid level sensor data to expected data. A filter permeability condition could be indicated when the reductant dosage rate exceeds the rate at which fluid can move through the stocking filter from the inlet volume (25) to the outlet volume (26). A filter transmittance condition may eventually lead to system failure.

Description

Technical area

The present disclosure generally relates to detecting the decrease in filter permeability in a reductant dosing system for exhaust aftertreatment of a diesel engine, and more particularly to a strategy for detecting impaired permeability of a sock filter in a reductant tank.

background

Many machines that use a diesel engine for propulsion today include exhaust aftertreatment systems. One purpose of these aftertreatment systems is to reduce the presence of NOx on the exhaust gas exhaust. Typically, this is accomplished by injecting a reductant, such as urea, into the exhaust pipe upstream of a selective catalytic reduction (SCR) catalyst where the NOx is converted to nitrogen and other, more acceptable compounds. The reducing agent, or urea, used for this process is supplied by a tank carried by the machine. If the tank needs to be filled, dirt and impurities can enter the tank together with the reducing agent. The risk of dirt and debris entering the reductant tank can be much more problematic in off-highway machines operating in heavily polluted or polluted environments.

Soon after the introduction of reductant dosing systems, diagnostic strategies have been developed to detect errors that would prevent the system from working properly. For example, reducing agent metering injectors require minimal fluid pressure to operate properly. In addition, the nozzle outlets of the reductant injector must remain open and free of blockages. Published US Patent Application 2012/0286063 teaches a urea injector diagnostic strategy that detects system errors in part by monitoring the supply line pressure for the reductant meter injector.

The regulations and other concerns often require a faulty reductant dosing system to be maintained as quickly as possible to keep the aftertreatment system compliant. Thus, when detecting a defect in the reductant system, the machine often has to be taken out of service for immediate maintenance, resulting in unexpected loss of working time and expensive repairs, along with a temporary loss of productivity leading to cascade effects in a larger multi-machine project can lead. These costly idle times could be avoided if symptoms that suggest an impending error can be detected early so that maintenance can be scheduled at an appropriate time rather than waiting and responding only after an error has occurred.

The present disclosure addresses one or more of the problems set forth above.

Summary

In one aspect, an engine is mounted on a chassis and includes an exhaust aftertreatment system. The exhaust aftertreatment system includes a reductant dosing system having a reductant tank with a fluid level sensor in communication with an electronic control unit. The reducing agent tank includes a filter that separates an intake volume from an exhaust volume. The fluid level sensor is positioned in the outlet volume. The tank includes an inlet that opens toward the inlet volume and an outlet that opens to the outlet volume. The electronic control unit includes a filter state algorithm configured to detect a filter permeability state based at least in part on data from the fluid level sensor.

In another aspect, a method of operating a machine includes operating an engine that is supported on a chassis of the machine. Exhaust gas is moved away from the engine through an exhaust pipe. Reducing agent is circulated in a fluid circuit from an outlet volume of a reducing agent tank, through a pump and into a return line which opens back into the outlet volume. The reducing agent is metered into the exhaust pipe of the engine. The reducing agent is moved from the inlet volume to the outlet volume of the reducing agent tank through a filter. Tank level data is communicated to an electronic controller by a fluid level sensor positioned in the outlet volume. The tank level data is compared with the expected data. A filter transmittance state is recorded in response to the tank level data differing from the expected data by more than a predetermined threshold.

Brief description of the drawings

1 FIG. 10 is a side view of a machine according to an aspect of the present disclosure; FIG.

2 FIG. 10 is a schematic view of an engine and exhaust aftertreatment system according to the present disclosure; FIG.

3 FIG. 10 is an exploded view of a reducing agent tank collector and a stocking filter according to the present disclosure; FIG.

4 FIG. 12 is a schematic view of a reducing agent tank showing a filter permeability state according to the present disclosure; FIG. and

5 FIG. 3 is a logic flow diagram of a reductant dosing algorithm that includes a filter state algorithm according to the present disclosure.

Detailed description

First, referring to 1 and 2 , includes a machine 10 an engine 15 who is on a landing gear 11 is mounted. The engine includes an exhaust aftertreatment system 16 , In the illustrated embodiment, the machine is 10 presented as a mobile, all-terrain backhoe loader in which the landing gear 11 from a drive 12 will be carried. However, those skilled in the art will recognize that a machine according to the present disclosure may also be stationary, such that the engine could be mounted on a fixed frame, or the frame could be the fuselage of a deep-sea vessel without departing from the present disclosure. The machine 10 includes an operator station 13 , which includes various system state indicators of a type well known in the art. However, those skilled in the art will recognize that in other versions of the invention, the system state information may be transmitted to a remote location, such as in the case of a stationary generator, for example.

The exhaust aftertreatment system 16 includes a reductant dosing system 20 that has a reducing agent tank 21 with a fluid level sensor 22 in communication with an electronic control unit 23 having. As used in this disclosure, the term "electronic controller" means one or more electronic controllers that may or may not communicate with one another in a manner known in the art. If the engine 15 runs, injects the reductant dosing system 20 Reducing agent, such as urea, in an exhaust pipe 17 for a NOx reduction reaction on the SCR catalyst 38 to promote. The electronic control unit 23 may be configured to reduce the reductant dosage rate of the injector 34 to adjust the NOx content in the exhaust stream to avoid ammonia slip or NOx slip at the exhaust, where the exhaust aftertreatment system bleeds off the treated engine exhaust gases to the atmosphere.

The reducing agent tank 21 includes a filter 24 that has an intake volume 25 from an outlet volume 26 separates. The fluid level sensor 22 which may be a float sensor is in the outlet volume 26 positioned. The Tank 21 also includes an inlet 27 that is related to the intake volume 25 opens, and an outlet 28 that is related to the outlet volume 26 opens. For purposes of illustration, the inlet is 27 to the reducing agent tank 21 on the outer surface of the machine 10 represented and serves as the means by which the tank 21 can be periodically filled with reducing agent as needed. If the inlet 27 For filling, dirt and debris have the opportunity to enter the intake volume 25 penetrate, especially in the case of all-terrain machines where both the machine 10 As well as the reducing agent filling position (not shown) are often exposed to dirt and impurities or covered by these. The filter 24 is included to prevent dirt and debris from entering the intake volume 25 enter, also in the outlet volume 26 reach. In the illustrated embodiment, the filter is 24 shown as a sock filter, but could have other configurations depending on the structure of the respective reductant tank. For example, the reductant tank could also be configured to simply separate the inlet volume from the outlet volume by a vertical wall that includes a wall filter without departing from the intended scope of the present disclosure.

During typical operation, the electronic control unit activates 23 a reducing agent pump 31 to the circulation of reducing agent in a fluid circuit 30 to start after the engine 15 was started. The fluid circuit 30 includes an outlet 28 , a pump 31 and a return line 32 that are in the outlet volume 26 opens. A second filter 33 is in the fluid circuit 30 positioned. The pump 31 Reductant fluid may initially pass through a sieve filter 39 that in an outlet volume 26 is placed behind the outlet 28 and then through the filter 33 pull it off before it either at the injector 34 arrives or via the return line 32 to the outlet volume 26 is returned. Thus, if no reductant from the injector 34 is injected, the total reducing agent is that of the outlet volume 26 through the pump 31 is pumped, for circulation via the return line 32 recycled. However, if the reductant dosing is active, and reductant will pass through the injector 34 in the exhaust pipe 17 dosed, will not that total reducing agent, which is the outlet volume 26 leaves, via the return line 32 recycled. When this happens, the reducing agent flows in the intake volume 25 through the stocking filter 24 in the outlet volume 26 to the fluid level of the reducing agent 37 in the intake volume 25 equal to that in the outlet volume 26 to keep. As known in the art, the filter can 33 be provided to prevent any substance particles passing through both the stocking filter 24 as well as the sieve filter 39 have arrived, possibly the nozzle outlets of the injector 34 clog. A pressure regulator 40 , which is shown here as a flow restriction, serves to control the pressure in the fluid circuit 30 to keep at injection level. The electronic control unit 23 can the pressure in the fluid circuit 30 via a pressure sensor 35 monitor. Although this is not necessary, the pump can 31 have the possibility of variable output (eg variable speed).

This allows the electronic control unit 23 which is in control communication with the pump 31 is the pumping rate in response to the system pressure supplied by the pressure sensor 35 is communicated, increase or decrease. The electronic control unit 23 also includes a filter state algorithm configured to set a filter transmittance state for the filter 24 based at least in part on data from the fluid level sensor 22 connected to the electronic control unit 23 be communicated to capture.

In addition, referring to 3 can the reducing agent tank 21 a collector 29 comprising an annular surface which is the open end of the sock filter 24 receives. Although other strategies could fall within the scope of the present disclosure, in the illustrated embodiment, the sock filter is 24 at the collector 29 with a suitable clamp 36 appropriate. As a reductant dosing system 20 over many cycles of emptying and filling with reducing agent 37 operated, carry dirt and contaminants into the intake volume 25 penetrate, eventually causing the permeability of the stocking filter 24 subsides. If the permeability has dropped too far, the dosing rate at the injection nozzle can be reduced 34 exceed the rate with the reductant from the intake volume 25 through the filter 24 and in the outlet volume 26 can flow. An exemplary filter permeability state is, for example, in 4 shown. If a filter permeability condition prevails, the reductant dosing system may 20 continue to be fully operational without reduced performance. In prior art systems, this system transmittance condition would go undetected or unnoticed. The present disclosure is based on the insight that, if the filter permeability condition can be detected while the reductant system is fully operational, maintenance of the reductant system 20 can be scheduled for a suitable time to the filter 24 before the filter permeability state becomes so serious that an actual system failure occurs.

Are the electronic control unit 23 and the pump 31 being unable to maintain the system pressure above a minimum injection pressure, a system error is generated and the reductant dosing system may be deactivated. Other modes of failure (eg, clogged injector) are known to those skilled in the art. A sudden system error may require that the machine 10 for immediate and costly maintenance at an unplanned time, disrupting site organization and hindering productivity. While reductant dosing systems may be subject to a regular maintenance schedule, the environment in which the machine 10 The detection of a filter permeability state according to the present disclosure may provide an early warning of impending system failure while the reductant system is being considered, or not considered 20 fully operational. Thus, the electronic control unit 23 comprise a reductant system fault algorithm configured to capture a reductant system fault in response to the pressure in the fluid circuit 30 of the reducing agent system 20 falls below a Dosierdruckschwelle, which for the correct operation of the injector 34 necessary is. The reductant system error algorithm may be configured for the reductant system 20 Disable in response to the reductant system error. In contrast, the electronic control unit 23 be adapted to the reducing agent system 20 in operation in response to a filter permeability condition.

The filter state algorithm according to the present disclosure may be configured to determine a time rate of change in the tank level data provided by the float sensor 22 be communicated. The filter state algorithm may be configured to record a filter transmittance state in response to the time rate of change in the tank level data being greater than an expected rate of time change while reducing agent 37 from the injector 34 in the exhaust pipe 17 of the motor 15 is dosed. In general, the electronic control unit should 23 know the reductant dosing rate, and therefore can estimate the rate at which the tank level should fall in response to the dosing rate. However, if a filter permeability condition prevails, the fluid level in the outlet volume 26 fall faster than the tank level should fall in response to this dosing rate. This condition is for example in 4 illustrated. When this happens, a filter permeability condition is detected and the operator can be alerted in an appropriate manner to allow replacement of the stocking filter 24 the task list of the next regular maintenance of the machine 10 can be added to prevent unplanned downtime and proactively prevent future system failure.

The present disclosure also contemplates another opportunity to detect a filter permeability condition. For example, when the engine is placed in a different state, such as a shutdown routine, when the reductant dosing is suspended, the filter state algorithm may also be configured to record a filter transmittance condition in response to an increase in tank level data being greater than an expected threshold After exposure to the reducing agent metering and the inlet 27 has been closed. Such a condition is indicated when the reducing agent in the fluid circuit 30 from the reducing agent system 20 is drained during an engine shutdown, resulting in excess reductant in the exhaust volume 26 returns, but the filter permeability state prevents the momentarily higher fluid level in the outlet volume 26 in a reverse direction through the filter 24 flows to the fluid level in the intake volume 25 compensate. When a filter permeability condition is detected in this manner, the operator may again be notified or alerted in a conventional manner, and the replacement of the stocking filter may be subject to the next maintenance schedule for the machine 10 from the operator, or optionally automatically by the electronic control unit 23 in a known way, to be added.

Industrial Applicability

The present disclosure finds potential applications in any engine comprising an engine with a reductant dosing system. The present disclosure finds particular application for machines operating in heavily polluted or contaminated environments that increase the likelihood of contaminants finding a way into a reductant tank. Finally, the present disclosure finds application in any reductant dosing system in which an inlet volume of the tank is separated from an outlet volume by a filter element to be serviced.

Now additionally referring to 5 FIG. 10 includes an exemplary logic flow diagram of a reductant dosing algorithm 50 both a system error algorithm 56 as well as a filter state algorithm 55 according to the present disclosure. It will be apparent to those skilled in the art that the reductant dosing algorithm 50 in connection with the regular operation of the machine 10 can be executed. At the oval 60 becomes the engine 15 started and continues in a conventional manner, leaving exhaust from the engine 15 through the exhaust pipe 17 is moved. At the block 61 activates the electronic control unit 23 the reducing agent pump 31 , This leads to reducing agents 37 through the fluid circuit 30 from the outlet volume 26 of the reducing agent tank 21 through the pump 31 and in the return line 32 circulates back into the outlet volume 26 opens. While the engine 15 continues to run, is the aftertreatment system 16 at block 62 warmed up to the correct treatment temperatures. In the query 63 answers the electronic control unit 23 the question of whether the aftertreatment system 16 warmed up to the correct operating temperatures. If not, the logic loops back and leaves the aftertreatment system at block 62 continue to warm up. If so, the logic can go to the block 64 go on where the electronic control unit 23 determine a desired dosage rate using other logic elements not within the scope of this disclosure. For example, these logic elements may attempt to set a dosage rate such that the NOx production rate of the engine 15 corresponds, as previously explained. Next is at block 65 the pressure of the reductant dosing system through the pressure sensor 35 measured. At block 66 become the reductant tank level data from the fluid level sensor 22 to the electronic control unit 23 communicated. When asked 67 determines the logic, if the system pressure too low for the correct operation of the injector 34 is. Since the system pressure could drop incrementally during normal operation, the electronic control unit may 23 by incrementally increasing the speed of the pump 31 react. Finally, however, the rate of the pump 31 reach their maximum allowable rate. When the pump 31 can no longer maintain the correct system pressure, results in the query 67 a yes, and the logic stops at block 81 a system error. Next, the operator at block 82 be alerted, and the reductant dosing system at block 83 be deactivated. The skilled person will recognize that the system error algorithm 56 can be much more complicated for an actual system and an incremental tuning of the engine 15 as an incentive for an operator to engage in maintenance before the reductant dosing system completes disabled and the engine 15 is completely stalled to force the operator to service the machine 10 appeal. If a system error occurs, the logic stops at the oval 84 ,

Returns the query 67 a negative answer back, the logic goes by block 68 continues, and reducing agent is in the exhaust pipe 17 of the motor 15 dosed. This should cause reducing agent from the inlet volume 25 in the outlet volume 26 through the filter 24 is moved to replenish the metered reducing agent. At block 69 the logic determines a rate of change of time in the tank level data collected by the float sensor 22 come. When asked 70 The logic asks if the tank level in the exhaust volume 26 Faster than expected. For example, if the dosage rate exceeds the rate with the fluid through the filter medium 24 can happen, the level falls in the outlet volume 26 faster than the level in the intake volume 25 , leading to the schematic in 4 illustrated filter permeability state leads. If so, the logic moves to block 71 where the filter permeability condition is noted. Next is at block 72 the operator is alerted about the condition. At block 73 may be an exchange of the stocking filter 24 to the task list for the next maintenance of the machine 10 to be added. Thus, the filter state algorithm draws 55 a filter transmittance state in response to the tank level data deviating from the expected data by more than a predetermined threshold, which avoids false detections that might otherwise occur due to causes such as abrupt engine movement and the like. The filter state algorithm 55 can compare the tank level data with the expected data. Although the present disclosure teaches the detection of filter transmittance conditions by examining the time rate of change in the tank level data, those skilled in the art will appreciate that properly timed torque data could be used without even determining a time rate of change without departing from the present disclosure.

After the query 70 Whether or not a filter transmittance condition is detected may be used by the logic to query 74 go on to determine if the engine has been stopped. Those skilled in the art will recognize that in many modern engines, engine shutdown may be a process that takes several seconds to several minutes to properly shut off all subsystems of the engine before the engine is shut down. If the query 74 returns a negative response, the logic loops back to block 64 determine the dosage rate, and repeat the determinations, measurements and queries as in 5 shown. Returns the query 74 returns a positive response, as part of engine shutdown, the reductant dosing is blocked 75 suspended, such as when the engine is placed in an idle state, before it is completely turned off. When asked 76 The filter state algorithm queries if the tank level in the exhaust volume 26 increases too much, because too much reducing agent from the fluid circuit 30 is deducted. This aspect of the logic assumes that the filter state algorithm 23 during a normal engine shutdown, the fluid volume of the fluid circuit 30 and the rate at which fluid enters the tank 21 returns when the reductant dosing is exposed knows. When the fluid level in the outlet volume 26 increases too much, the query goes to block 77 and maintains a filter permeability condition as the circumstances indicate that the fluid is due to the decreasing permeability in the filter 24 only with difficulty from the outlet volume 26 into the intake volume 25 emotional. At block 78 the operator can be alerted, and at block 79 may require a replacement of the stocking filter to the task list for the next machine maintenance 10 to be added. If the query 76 returns a negative answer, the logic moves to the oval 80 continues to end, indicating a correct engine shutdown.

The abbreviated version of a reductant system error algorithm 56 is in the reductant dosing algorithm 50 included to isolate a system error from a system state. In other words, a system failure, if ignored, will eventually deactivate the reductant dosing system 20 to lead. However, detection of a filter permeability condition is handled differently by the electronic controller being able to operate the reductant dosing system in response to a filter permeability condition. In the illustrated embodiment, the screen filter 39 and the fine particle filter 33 in order to contrast these known system filters with the additional hosiery and filter state algorithm of the present disclosure. Thus, the pump pumps 31 Reducing agent through the filter 33 but gravity may allow for the movement of reducing fluid between the intake volume 25 and the outlet volume 26 through the stocking filter 24 to be responsible. Those skilled in the art will recognize that the expected time rate of change in the tank level data is based on the known metering rate commanded during normal system operation and an understanding of the fluid surface in the tank 21 can be based.

By detecting a filter transmittance condition, an operator can be alerted of an impending error, while still allowing the system to remain fully operational and keeping the machine productive. This early alarm allows maintenance of the reductant system to be added to a previously scheduled maintenance schedule to avoid any unexpected failure and the associated costs and project interruptions. Thus, the teachings of the present disclosure may be useful to proactively ensure proper maintenance of the reductant dosing system 20 before an otherwise unavoidable error, the possible shutdown of the reducing agent system and the shutdown of the associated machine 10 requires planning. Replacement of a stocking filter according to the present disclosure can be accomplished by removing the head 29 from the tank 21 , Loosen the clamp 36 and then pushing down the sock filter 24 from the head 29 be achieved. A new stocking filter 24 can then be used in the opposite way. As this happens, the technician may take the opportunity to discuss other aspects of the reductant dosing system 20 to inspect and / or wait for the productivity of the machine 10 maintain and prevent premature failure of the reductant system.

The present description is for the purpose of illustration only and should not be construed as limiting the scope of the present disclosure in any way. It will be apparent to those skilled in the art that various modifications of the embodiments disclosed herein may be made without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features, and advantages will become apparent upon review of the attached drawings and the following claims.

Claims (10)

Machine ( 10 ), comprising: an engine ( 15 ) mounted on a chassis ( 11 ) and an exhaust aftertreatment system ( 16 ); wherein the exhaust aftertreatment system ( 16 ) a reductant dosing system ( 20 ) comprising a reducing agent tank ( 21 ) with a fluid level sensor ( 22 ) in communication with an electronic control unit ( 23 ) having; wherein the reducing agent tank ( 21 ) a filter ( 24 ) having an intake volume ( 25 ) of an outlet volume ( 26 ) and the fluid level sensor ( 22 ) in the outlet volume ( 26 ), and the reducing agent tank ( 21 ) an inlet ( 27 ), which corresponds to the intake volume ( 25 ) and an outlet ( 28 ), which corresponds to the outlet volume ( 26 ) opens; and wherein the electronic control unit ( 23 ) a filter state algorithm ( 55 ) configured to determine a filter permeability state based at least in part on data from the fluid level sensor (11). 22 ) capture. Machine ( 10 ) according to claim 1, wherein the fluid level sensor ( 22 ) is a float sensor; and the filter ( 24 ) is a sock filter; and a collector ( 29 ) of the reducing agent tank ( 21 ) and the stocking filter the outlet volume ( 26 ) define. Machine ( 10 ) according to claim 2, wherein the electronic control unit ( 23 ) a reductant system error algorithm ( 56 ) configured to generate a reductant system error in response to a pressure in a fluid circuit ( 30 ) of the reducing agent system ( 20 ), which is lower than a Dosierdruckschwelle; and wherein the system error algorithm ( 56 ) is adapted to the reducing agent system ( 20 ) in response to a reductant system failure; and the electronic control unit ( 23 ) is adapted to the reducing agent system ( 20 ) to maintain operable in response to the filter permeability condition. Machine ( 10 ) according to claim 3, wherein the fluid circuit ( 30 ) the outlet ( 28 ), a pump and a return line extending to the outlet volume ( 26 ) opens; a second filter ( 24 ) located in the fluid circuit ( 30 ) is positioned; the filter state algorithm ( 55 ) is adapted to determine a time change rate in the tank level data; and wherein the filter state algorithm ( 55 ) is configured to record a filter permeability state in response to the time rate of change in the tank level data being greater than an expected time rate of change, while reducing agent is used by the reductant system ( 20 ) in an exhaust pipe ( 17 ) of the motor ( 15 ) is metered. Machine ( 10 ) according to claim 4, wherein the filter state algorithm ( 55 ) is configured to hold a filter permeability state in response to an increase in the tank level data that is greater than an expected elevation threshold after exposing the reductant doser and the inlet ( 27 ) has been closed. Method for operating a machine ( 10 ), comprising the steps of: operating an engine ( 15 ) mounted on a chassis ( 11 ) the machine ( 10 ) will be carried; Moving away exhaust gas from the engine ( 15 ) through an exhaust pipe ( 17 ); Circulating reducing agent in a fluid circuit ( 30 ) of an outlet volume ( 26 ) of a reducing agent tank ( 21 ), by a pump ( 31 ) and in a return line ( 32 ), which fall back into the outlet volume ( 26 ) opens; Dosing of reducing agent in an exhaust pipe ( 17 ) of the motor ( 15 ); Moving reductant from the intake volume ( 25 ) to the outlet volume ( 26 ) through a filter ( 24 ); Communicating tank level data from a fluid level sensor ( 22 ) contained in the outlet volume ( 26 ) to an electronic control unit ( 23 ); Comparing the tank level data with expected data; and maintaining a filter transmittance condition in response to the tank level data differing from the expected data by more than a predetermined threshold. The method of claim 6, wherein the recirculating step comprises pumping the reductant through a second filter (10). 24 ) fluidly in the fluid circuit ( 30 ) is positioned. Method according to claim 7, comprising the step of measuring a system pressure of the reducing agent in the fluid circuit ( 30 ); Detecting a reductant system failure in response to the system pressure being below a dosing pressure threshold; Commissioning the reducing agent system ( 20 ) in response to the filter permeability state; and deactivating the reductant dosage system ( 20 ) in response to the reducing agent system error.  The method of claim 8, wherein the comparing step comprises comparing a time rate of change in the tank level data with an expected time rate of change; determining a dosage rate; and determining the expected time rate of change based at least in part on the dosage rate. Method according to claim 9, comprising subjecting the metering of reducing agent into the exhaust pipe ( 17 ); wherein the comparing step comprises detecting an increase in the tank level data that is greater than an expected increase threshold after the dosage has been suspended; Exposing the metering of reducing agent in the exhaust pipe ( 17 ); wherein the recording step comprises detecting an increase in the tank level data that is greater than an expected increase threshold after the dosage has been suspended; Replacing the stocking filter in response to the filter permeability condition; and adding a stocking filter exchange to a previous maintenance schedule for the machine ( 10 ) in response to the filter permeability state.

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