Patent Application
20150218990
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.
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.
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.
Referring initially to
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
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
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.
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
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
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
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.
