US20150218990A1

US20150218990A1 - Diesel exhaust fluid filter permeability detection strategy and machine using same

Info

Publication number: US20150218990A1
Application number: US14/170,857
Authority: US
Inventors: Jason Wesley Hudgens
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2014-02-03
Filing date: 2014-02-03
Publication date: 2015-08-06
Also published as: CN105940197A; DE112015000334T5; WO2015117114A1; CN105940197B

Abstract

A reductant dosing system for an exhaust aftertreatment system of a diesel engine includes a reductant tank with an inlet volume separated from an outlet volume by a sock filter. A filter permeability condition is detected by the electronic controller using a filter status algorithm that compares fluid level sensor data to expected data. A filter permeability condition might be indicated when the reductant dosing rate exceeds the rate at which fluid can move through the sock filter from the inlet volume to the outlet volume. A filter permeability condition may eventually lead to a system fault.

Description

TECHNICAL FIELD

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

BACKGROUND

Many machines that utilize a diesel engine for power now include exhaust aftertreatment systems. One purpose of these aftertreatment systems is to reduce the presence of NOx at the exhaust tailpipe. Typically, this is accomplished by injecting a reductant, such as urea, into the exhaust pipe upstream from a selective catalytic reduction (SCR) catalyst, where the NOx is converted to nitrogen and other more acceptable compounds. The reductant, or urea, utilized for this process is supplied from a tank carried by the machine. When the tank is in need of being refilled, dirt and debris can enter the tank along with the reductant. The risk of dirt and debris entering the reductant tank can be many times more problematic in the case of off road machines that must operate in dirt and debris filled environments.
Soon after the adoption of reductant dosing systems there were diagnostic strategies to detect faults that would prevent the system from operating properly. For instance, reductant dosing injectors require some minimum fluid pressure in order to operate properly. Furthermore, the nozzle outlets of the reductant injector must remain open and free of clogs. U.S. Patent Application Publication 2012/0286063 teaches a urea injector diagnostic strategy that detects system faults in part by monitoring delivery line pressure for the reductant dosing injector.
Regulations and other concerns often require that a faulted reductant dosing system be serviced as soon as possible in order to maintain the aftertreatment system in compliance. Thus, when a reductant system fault is detected, the machine must often be brought offline for immediate servicing, with the result being an unexpected loss of work time and expensive repairs, along with a temporary loss in productivity that can have cascading effects elsewhere in a larger project involving many machines. These costly downtimes might be avoided if symptoms that suggest a forthcoming fault can be detected early so that servicing can be scheduled at a convenient time, rather than waiting and responding after a fault occurs.
The present disclosure is directed toward 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 that has a reductant tank with a fluid level sensor in communication with an electronic controller. The reductant tank includes a filter separating an inlet volume from an outlet volume. The fluid level sensor is positioned in the outlet volume. The tank includes an inlet that opens to the inlet volume, and an outlet that opens to the outlet volume. The electronic controller includes a filter status algorithm configured to detect a filter permeability condition based at least in part on data from the fluid level sensor.
In another aspect, a method of operating a machine includes running an engine supported on a chassis of the machine. Exhaust is moved through an exhaust pipe from the engine. Reductant is circulated around a fluid circuit from an outlet volume of a reductant tank, through a pump and into a return line that opens back into the outlet volume. Reductant is dosed into the exhaust pipe of the engine. Reductant is moved from the inlet volume to the outlet volume of the reductant tank through a filter. Tank level data is communicated from a fluid level sensor, which is positioned in the outlet volume, to an electronic controller. Tank level data is compared to expected data. A filter permeability condition is logged responsive to the tank level data differing from the expected data by greater than a predetermined threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

FIG. 3 is an exploded view of a reductant tank header and a sock filter according to the present disclosure;

FIG. 4 is a schematic view of a reductant tank showing a filter permeability condition according to the present disclosure; and

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

DETAILED DESCRIPTION

Referring initially to FIGS. 1 and 2, a machine 10 includes an engine 15 mounted on a chassis 11. The engine includes an exhaust aftertreatment system 16. In the illustrated embodiment, machine 10 is shown as a mobile backhoe loader off-road machine in which chassis 11 is supported by a conveyance 12. Nevertheless, those skilled in the art will appreciate that a machine according to the present disclosure could also be stationary, such that the engine were supported on a stationary chassis, or the chassis could be the hull framework of a seagoing vessel without departing from the present disclosure. Machine 10 includes an operator station 13 that includes various system status displays of a type well known in the art. Nevertheless, those skilled in the art will appreciate that in other versions of the invention system status information may be transmitted to a remote location, such as for instance in the case of a stationary generator.
The exhaust aftertreatment system 16 includes a reductant dosing system 20 that includes a reductant tank 21 with a fluid level sensor 22 in communication with an electronic controller 23. As used in this disclosure, “electronic controller” means one or more electronic controllers that may or may not communicate with each other in a manner known in the art. When engine 15 is operating, reductant dosing system 20 injects reductant, such as urea, into an exhaust pipe 17 to facilitate a NOx reduction reaction at SCR catalyst 38. Electronic controller 23 may be configured to control the reductant dosing rate from injector 34 in order to match the NOx content in the exhaust stream so as to avoid either ammonia slip or NOx slip at the tailpipe where the exhaust aftertreatment system vents the treated engine exhaust to atmosphere.
The reductant tank 21 includes a filter 24 separating an inlet volume 25 from an outlet volume 26. The fluid level sensor 22, which may be a float sensor, is positioned in the outlet volume 26. Tank 21 also includes an inlet 27 that opens to the inlet volume 25 and an outlet 28 that opens to the outlet volume 26. For illustrative purposes, the inlet 27 to reductant tank 21 is shown on the outer surface of machine 10 and serves as the means by which tank 21 may be periodically refilled with reductant as needed. When inlet 27 is opened for refilling, debris and dirt have an opportunity to enter inlet volume 25, especially in the case of off-road machines where both the machine 10 and the reductant refill location (not shown) are exposed to, and often covered, with debris and dirt. Filter 24 is included to prevent the dirt and debris that enters into inlet volume 25 from entering into the outlet volume 26. In the illustrated embodiment, filter 24 is shown as a sock filter, but could take other configurations depending upon the structure of the particular reductant tank. For instance, the reductant tank could be configured to simply separate the inlet volume from the outlet volume by a vertical wall which would include a wall filter without departing from the intended scope of the present disclosure.
During typical operation, electronic controller 23 will activate a reductant pump 31 to begin circulating reductant in a fluid circuit 30 after engine 15 is started. Fluid circuit 30 includes outlet 28, pump 31 and return line 32 that opens into outlet volume 26. A second filter 33 is positioned in fluid circuit 30. Pump 31 may draw reductant fluid initially through a screen filter 39 located in outlet volume 26, past outlet 28 and then through filter 33 prior to either arriving at injector 34 or being returned to outlet volume 26 via return line 32. Thus, when no reductant is being injected from injector 34, all of the reductant pumped from outlet volume 26 by pump 31 is returned for recirculation via return line 32. However, when reductant dosing is active and reductant is being dosed through injector 34 into exhaust pipe 17, less than all of the reductant leaving outlet volume 26 is returned via return line 32. When this occurs, reductant in inlet volume 25 flows through sock filter 24 into outlet volume 26 in order to maintain the fluid level of reductant 37 in inlet volume 25 equal to that in outlet volume 26. As is known in the art, filter 33 may be provided to prevent any tiny particulate matter that passed through both sock filter 24 and screen filter 39 from potentially plugging the nozzle outlets of injector 34. A pressure regulator 40, which is shown as a flow restriction, serves to help maintain injection level pressure in fluid circuit 30. Electronic controller 23 may monitor pressure and fluid circuit 30 via a pressure sensor 35. Although not necessary, pump 31 may have a variable output capability (e.g. variable speed). This permits electronic controller 23 is in control communication with pump 31 to increase or decrease the pump rate responsive to system pressure as communicated by pressure sensor 35. Electronic controller 23 also includes a filter status algorithm configured to detect a filter permeability condition for filter 24 based at least in part on data from fluid level sensor 22 communicated to electronic controller 23.
Referring now in addition to FIG. 3, reductant tank 21 may include a header 29 with an annular surface that receives the open end of sock filter 24. Although other strategies could fall within the scope of the present disclosure, in the illustrated embodiment, sock filter 24 is attached to header 29 with a suitable clamp 36. As a reductant dosing system 20 operates over many cycles of being emptied and refilled with reductant 37, the dirt and debris entering inlet volume 25 will eventually begin to degrade the permeability of sock filter 24. When the permeability is sufficiently degraded, the dosing rate at injector 34 may exceed the rate at which reductant can flow from inlet volume 25 through filter 24 and into outlet volume 26. An example circumstance in which a filter permeability condition exists is shown, for example, in FIG. 4. Thus, when a filter permeability condition exists, the reductant dosing system 20 may continue to be fully operational without any degraded performance. In prior art systems, this system permeability condition would go undetected and unnoticed. The present disclosure insightfully recognizes that if the filter permeability condition can be detected while the reductant system is fully operational, maintenance on the reductant system 20 can be scheduled at a convenient time to replace filter 24 before the filter permeability condition becomes so severe that an actual system fault Occurs.
If electronic controller 23 and pump 31 are unable to maintain system pressure above some minimum injection pressure, a system fault will be generated and the reductant dosing system may be disabled. Other fault modes (e.g. plugged injector) are known to those skilled in the art. A sudden system fault can require that the machine 10 be shut down for immediate and costly maintenance at an unscheduled time disrupting worksite organization and undermining productivity. While reductant dosing systems may be on some regular maintenance schedule that does or does not take into account the environment in which the machine 10 is operating, detection of a filter permeability condition according to the present disclosure can provide early warning of a forthcoming system fault while the reductant system 20 remains fully operational. Thus, electronic controller 23 may include a reductant system fault algorithm configured to log a reductant system fault responsive to pressure in fluid circuit 30 of reductant system 20 falling to less than a dosing pressure threshold necessary for proper operation of injector 34. The reductant system fault algorithm may be configured to disable the reductant system 20 responsive to the reductant system fault. In contrast, electronic controller 23 may be configured to maintain the reductant system 20 operational responsive to a filter permeability condition.
The filter status algorithm according to the present disclosure may be configured to determine a time rate of change in the tank level data communicated by float sensor 22. The filter status algorithm may be configured to log a filter permeability condition responsive to the time rate of change in the tank level data being greater than an expected time rate of change while reductant 37 is being dosed from injector 34 into exhaust pipe 17 of engine 15. In general, electronic controller 23 should know the reductant dosing rate and can estimate the rate at which the tank level should fall responsive to that dosing rate. However, if a filter permeability condition exists, the fluid level in outlet volume 26 may fall faster than the tank level ought to fall responsive to that dosing rate. This condition, for instance is illustrated in FIG. 4. When this occurs, a filter permeability condition is detected, and the operator may be alerted in a suitable manner so that changing of the sock filter 24 may be added to the next regular servicing agenda of machine 10, in order to avoid unscheduled down time and potentially proactively prevent a future system fault.
The present disclosure also contemplates another opportunity for detecting a filter permeability condition. For instance, when the engine is changed to a state, such as a shutdown routine, when reductant dosing is ceased, the filter status algorithm may also be configured to log a filter permeability condition responsive to an increase in the tank level data that is greater than an expected increase threshold, after reductant dosing has ceased and inlet 27 is closed. Such a circumstance is indicated when the reductant in fluid circuit 30 is evacuated from reductant system 20 during engine shutdown resulting in excess reductant returning to outlet volume 26, but the filter permeability condition prevents the briefly higher fluid level in the outlet volume 26 from passing in a reverse direction through filter 24 to balance with the fluid level in inlet volume 25. Again, when a filter permeability condition is detected in this manner, the operator may be notified or alerted in a conventional manner, and sock filter replacement may be added to a next servicing agenda for machine 10 by the operator or possibly automatically by electronic controller 23 in a known manner.

INDUSTRIAL APPLICABILITY

The present disclosure finds potential application in any machine that includes an engine with a reductant dosing system. The present disclosure finds specific applicability to machines that must operate in debris and dirt filled environments that increase the likelihood of contaminants finding their 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 serviceable filter element.
Referring now in addition to FIG. 5, an example logic flow diagram of a reductant dosing algorithm 50 that includes both a system fault algorithm 56 and a filter status algorithm 55 according to the present disclosure. Those skilled in the art will appreciate that the reductant dosing algorithm 50 may be executed in conjunction with regular operation of machine 10. At oval 60, engine 15 is started and proceeds to run in a conventional manner so that exhaust from engine 15 is moved through exhaust pipe 17. At box 61, electronic controller 23 activates reductant pump 31. This results in reductant 37 circulating around fluid circuit 30 from the outlet volume 26 of reductant tank 21, through pump 31 and into return line 32, which opens back into outlet volume 26. As engine 15 continues to run, the aftertreatment system 16 is warmed up to proper treatment temperatures at box 62. At query 63, electronic controller 23 answers the question of whether the aftertreatment system 16 is warmed up to proper operational temperatures. If not, the logic will loop back and continue to warm up the aftertreatment system at box 62. If affirmative, the logic may advance to box 64 where electronic controller 23 determines a desired dosing rate using other logic outside the scope of this disclosure. For instance, this logic may attempt to set a dosing rate to match the production rate of NOx from engine 15 as discussed earlier. Next at box 65, the reductant dosing system pressure is measured by pressure sensor 35. At box 66, the reductant tank level data from fluid level sensor 22 is communicated to electronic controller 23. At query 67, the logic determines whether system pressure is too low for proper operation of injector 34. During normal operation, as system pressure might incrementally drop, electronic controller 23 may incrementally respond by increasing the speed of pump 31. However, eventually, the rate of pump 31 will reach its maximum allowed rate. When the pump 31 can no longer maintain proper system pressure, query 67 will return a yes and the logic will log a system fault at box 81. Next, the operator may be alerted at box 82 and the reductant dosing system may be disabled at box 83. Those skilled in the art will appreciate that the system fault algorithm 56 according to an actual system may be substantially more complicated and allow for incrementally derating engine 15 as inducements for the operator to seek servicing prior to completely disabling the reductant dosing system and completely derate engine 15 in order to force the operator to seek servicing of machine 10. If a system fault occurs, the logic ends at oval 84.
If query 67 returns a negative, the logic advances to box 68 and reductant is dosed into exhaust pipe 17 of engine 15. This should result in movement of reductant from the inlet volume 25 into the outlet volume 26 through filter 24 in order to make up for the dosed reductant. At box 69, the logic determines a time rate of change in the tank level data originating from float sensor 22. At query 70, the logic asks whether the tank level in outlet volume 26 is dropping faster than expected. For instance, if the dosing rate exceeds the rate at which fluid can pass through filter medium 24, the level in the outlet volume 26 will drop faster than the level in inlet volume 25 resulting in a filter permeability condition schematically illustrated in FIG. 4. If so, the logic advances to box 71 where a filter permeability condition is logged. Next at box 72, the operator is alerted of the condition. At box 73, a sock filter 24 change may be added to the next servicing agenda for machine 10. Thus, the filter status algorithm 55 logs a filter permeability condition responsive to the tank level data differing from expected data by greater than some predetermined threshold that avoids false detections that might otherwise occur due to such causes as abrupt machine movements and the like. The filter status algorithm 55 may compare tank level data to expected data. Although the present disclosure teaches detection of filter permeability conditions by examining time rate of change in the tank level data, those skilled in the art will appreciate that properly timed snapshot data could be used without ever determining time rate of change and without departing from the present disclosure.
After query 70, whether or not a filter permeability condition is detected, the logic may advance to query 74 in order to determine whether engine shut down has been initiated. Those skilled in the art will appreciate that in many modern machines, engine shutdown may constitute a procedure that lasts several seconds to several minutes in order to properly shut down all of the engine subsystems before actually stopping the engine. If query 74 returns a negative, the logic loops back to again determine the dosing rate at box 64 and repeats the determinations measurements and queries as shown in FIG. 5. If query 74 returns a positive, as part of the engine shut down reductant dosing is ceased at box 75, such as when the engine is placed in an idle condition prior to being completely stopped. At query 76, the filter status algorithm queries whether the tank level in outlet volume 26 is increasing too much due to the evacuation of reductant from fluid circuit 30. This aspect of the logic suggests that the filter status algorithm 23 knows the fluid volume of fluid circuit 30 and the rate by which that fluid will return to tank 21 when the reductant dosing has ceased during a normal engine shut down procedure. If that fluid level in the outlet volume 26 is increasing too much, the query will move to box 77 and log a filter permeability condition because that circumstance indicates that fluid is having difficulty moving from the outlet volume 26 into the inlet volume 25 due to degraded permeability in filter 24. At box 78, the operator may be alerted and at box 79 the sock filter change may be added to the next servicing agenda for machine 10. If query 76 returns a negative, the logic advance to oval 80 to end indicating that a proper engine shut down.
The abbreviated version of a reductant system fault algorithm 56 is included in the reductant dosing algorithm 50 to contrast a system fault from a system condition. In other words, a system fault, if ignored, will eventually result in disabling the reductant dosing system 20. However, detection of a filter permeability condition is treated differently in that electronic controller may maintain the reductance dosing system operational responsive to a filter permeability condition. In the illustrated embodiment, the screen filter 39 and the fine particulate filter 33 are identified in order to contrast those known system filters with the added sock filter and filter status algorithm of the present disclosure. Thus, pump 31 pumps reductant through filter 33, but gravity may be responsible for movement of reductant fluid between inlet volume 25 and outlet volume 26 through sock filter 24. Those skilled in the art will appreciate that the expected time rate of change in the tank level data may be based upon the known dosing rate commanded during normal system operation and an understanding of the fluid surface area in tank 21.
By detecting a filter permeability condition, an operator can be alerted to a forthcoming fault while still being able to maintain the system fully operational and the machine productive. This early alert allows reductant system servicing to be added to a previously scheduled servicing agenda so that a surprise fault and its accompanying costs and project disruptions are avoided. Thus, the teachings of the present disclosure may be useful in proactively planning for proper servicing of the reductant dosing system 20 prior to an otherwise inevitable fault requiring the potential disablement of the reductant system and associated taking of machine 10 offline. Replacement of a sock filter according to the present disclosure can be accomplished by detaching the head 29 from tank 21, loosening clamp 36 and then sliding sock filter 24 free of head 29. A new sock filter 24 can then be replaced in a reverse manner. While this is being performed, the technician may utilize the opportunity to inspect and/or service other aspects of the reductant dosing system 20 in an effort to maintain machine 10's productivity and avoid untimely reductant system faults.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims.

Claims

What is claimed is:

1. A machine comprising:

an engine mounted on a chassis and including an exhaust after treatment system;

the exhaust after treatment system including a reductant dosing system that includes a reductant tank with a fluid level sensor in communication with an electronic controller;

the reductant tank including a filter separating an inlet volume from an outlet volume, and the fluid level sensor being positioned in the outlet volume, and the reductant tank including an inlet that opens to the inlet volume and an outlet that opens to the outlet volume; and

the electronic controller including a filter status algorithm configured to detect a filter permeability condition based at least in part on data from the fluid level sensor.

2. The machine of claim 1 wherein the fluid level sensor is a float sensor; and

the filter is a sock filter; and

a header of the reductant tank and the sock filter define the outlet volume.

3. The machine of claim 2 wherein the electronic controller includes a reductant system fault algorithm configured to log a reductant system fault responsive to a pressure in a fluid circuit of the reductant system that is less than a dosing pressure threshold.

4. The machine of claim 3 wherein the system fault algorithm is configured to disable the reductant system responsive to a reductant system fault; and

the electronic controller is configured to maintain the reductant system operational responsive to the filter permeability condition.

5. The machine of claim 4 wherein the fluid circuit includes the outlet, a pump and a return line that opens into the outlet volume; and

a second filter positioned in the fluid circuit.

6. The machine of claim 5 wherein the filter status algorithm is configured to determine a time rate of change in the tank level data; and

the filter status algorithm is configured to log a filter permeability condition responsive to the time rate of change in the tank level data being greater than an expected time rate of change while reductant is being dosed from the reductant system into an exhaust pipe of the engine.

7. The machine of claim 6 wherein the filter status algorithm is configured to log a filter permeability condition responsive to an increase in the tank level data that is greater than an expected increase threshold after reductant dosing has ceased and the inlet is closed.

8. The machine of claim 1 wherein the electronic controller includes a reductant system fault algorithm configured to log a reductant system fault responsive to a pressure in a fluid circuit of the reductant system that is less than a dosing pressure threshold;

the system fault algorithm is configured to disable the reductant system responsive to a reductant system fault;

the electronic controller is configured to maintain the reductant system operational responsive to the filter permeability condition;

the fluid circuit includes the outlet, a pump and a return line that opens into the outlet volume; and

a second filter positioned in the fluid circuit.

9. The machine of claim 1 wherein the filter status algorithm is configured to determine a time rate of change in the tank level data;

the filter status algorithm is configured to log a filter permeability condition responsive to the time rate of change in the tank level data being greater than an expected time rate of change while reductant is being dosed from the reductant system into an exhaust pipe of the engine; and

the filter status algorithm is configured to log a filter permeability condition responsive to an increase in the tank level data that is greater than an expected increase threshold after reductant dosing has ceased and the inlet is closed.

10. A method of operating a machine, comprising the steps of:

running an engine supported on a chassis of the machine;

moving exhaust through an exhaust pipe from the engine;

circulating reductant around a fluid circuit from an outlet volume of a reductant tank, through a pump and into a return line that opens back into the outlet volume;

dosing reductant into an exhaust pipe of the engine;

moving reductant from the inlet volume to the outlet volume through a filter;

communicating tank level data from a fluid level sensor, which is positioned in the outlet volume, to an electronic controller;

comparing the tank level data to expected data; and

logging a filter permeability condition responsive to the tank level data differing from the expected data by greater than a predetermined threshold.

11. The method of claim 10 wherein the circulating step includes pumping the reductant through a second filter fluidly positioned in the fluid circuit.

13. The method of claim 12 including a step of measuring a system pressure of the reductant in the fluid circuit;

logging a reductant system fault responsive to the system pressure being below a dosing pressure threshold.

14. The method of claim 13 including a step of maintaining the reductant dosing system operational responsive to the filter permeability condition; and

disabling the reductant dosing system responsive to the reductant system fault.

15. The method of claim 10 wherein the comparing step includes comparing a time rate of change in the tank level data to an expected time rate of change.

16. The method of claim 15 including determining a dosing rate; and

determining the expected time rate of change based at least in part on the dosing rate.

17. The method of claim 16 including ceasing dosing of reductant into the exhaust pipe;

the comparing step includes detecting an increase in the tank level data that is greater than an expected increase threshold after the dosing has ceased.

18. The method of claim 15 including ceasing dosing of reductant into the exhaust pipe;

the logging step includes detecting an increase in the tank level data that is greater than an expected increase threshold after the dosing has ceased.

19. The method of claim 10 including replacing the sock filter responsive to the filter permeability condition.

20. The method of claim 19 including adding sock filter replacement to a previous maintenance schedule for the machine responsive to the filter permeability condition.