Patent Application
20140331645
This disclosure relates generally to engine systems and, more particularly, to exhaust after-treatment systems and methods.
One known method for abating certain diesel engine exhaust constituents is by use of an exhaust after-treatment system that utilizes Selective Catalytic Reduction (SCR) of nitrogen oxides. In a typical SCR system, urea or a urea-based water solution is mixed with exhaust gas. In some applications, a urea solution is injected directly into an exhaust passage through a specialized injector device. The injected urea solution mixes with exhaust gas and breaks down to provide ammonia (NH3) in the exhaust stream. The ammonia then reacts with nitrogen oxides (NOx) in the exhaust at a catalyst to provide nitrogen gas (N2) and water (H2O).
As can be appreciated, SCR systems require the presence of some form of urea close to the engine system such that the engine can be continuously supplied during operation. Various urea or urea-solution delivery systems are known and used in engine applications. In known urea injection systems, temperature- and/or pressure-related challenges may arise that can affect the electronic and mechanical hardware used to inject the urea. For example, given that the urea is typically injected directly into the engine's exhaust system in an aqueous solution form, changes in the solution concentration due to thermal or pressure effects can impede proper injector function both during system operation as well as after heat saturation following a hot engine shut-down. Moreover, for systems using water-based urea solutions, boiling and/or depressurization of the system can result in crystallization of urea at the injector, which may plug the injector.
The disclosure describes, in one aspect, a machine. The machine includes an engine having an exhaust system associated therewith. A diesel exhaust fluid (DEF) injector is disposed to provide metered amounts of DEF into the exhaust system. The DEF injector includes a valve adapted to selectively open in response to a command for injecting DEF into the exhaust system. A controller is associated with the engine and the DEF injector. The controller is disposed to monitor operation of the DEF injector to detect a fault, activate a failure signal when a fault in the DEF injector is detected, and activate a failure remediation cycle while the failure signal is active. The remediation cycle includes causing an increase in a temperature of an exhaust gas in the exhaust gas system to heat the DEF injector and melt any urea crystals that may be causing the fault, and activating the valve of the DEF injector to evacuate molten urea from within the DEF injector. The controller furher determines whether the fault has been cleared, and resets the failure signal when the fault has been cleared.
In another aspect, the disclosure describes a method for failure remediation of a diesel exhaust fluid (DEF) injector in a machine having an engine, which includes an exhaust system. The method comprises generating exhaust gas and routing the same through an exhaust gas system. Predetermined quantities of a diesel exhaust fluid (DEF) containing an aqueous solution of urea are selectively injected into the exhaust gas using a DEF injector. The DEF injector is responsive to command signals provided by a controller. Operation of the DEF injector is monitored with the controller to detect a fault, and a failure signal is activated in the controller when a fault in the DEF injector is detected. A failure remediation cycle is activated in the controller while the failure signal is active. The remediation cycle includes causing an increase in a temperature of the exhaust gas in the exhaust gas system to heat the DEF injector above a normal operating temperature such that any urea crystals that may be causing the fault are melted. The DEF injector is then activated to evacuate molten urea from within the DEF injector.
In yet another aspect, the disclosure describes a method for remediating a fault in a DEF injector. The method includes determining that a fault is present in the DEF injector, which fault may be attributable to condensation of crystalline urea within the injector after boiling and evaporation of water from an aqueous urea solution has occurred within the DEF injector. A failure signal is activated when the fault in the DEF injector is present. The DEF injector is heated to a temperature that is above a normal operating temperature to melt any crystalline urea within the DEF injector. The DEF injector is activated to evacuate any molten urea from within the DEF injector, and a determination is made as to whether the fault has been remediated.
This disclosure relates to power management systems for machines and, more particularly, to power management systems and methods that prevent and, if necessary, remediate DEF injector plugging due to urea crystallization.
A side view of a machine 100, in this example a motor grader 101, is shown in
The motor grader 101 shown in
The engine frame 102 supports an engine (shown and described relative to
The transfer conduit 212 fluidly interconnects the first module 204 with a second module 214 such that exhaust gas from the engine 202 may pass through the first and second modules 204 and 214 in series before being released at a stack 220 that is connected to the second module. In the illustrated embodiment, the second module 214 encloses a SCR catalyst 216 and an Ammonia Oxidation Catalyst (AMOX) 218. The SCR catalyst 216 and AMOX 218 operate to treat exhaust gas from the engine 202 in the presence of ammonia, which is provided after degradation of a urea-containing solution injected into the exhaust gas in the transfer conduit 212.
More specifically, a urea-containing water solution, which is commonly referred to as diesel exhaust fluid (DEF) 221, is injected into the transfer conduit 212 by a DEF injector 222. The DEF 221 is contained within a reservoir 228 and is provided to the DEF injector 222 by a pump 226. As the DEF 221 is injected into the transfer conduit 212, it mixes with exhaust gas passing therethrough and is carried to the second module 214. To promote mixing of DEF with exhaust, a mixer 224 may be disposed along the transfer conduit 212.
As can be appreciated, the location of the DEF injector 222 on the transfer conduit 212 can expose the injector to relatively high temperatures due to heating from exhaust gas during operation. In the illustrated exemplary embodiment, a flow of engine coolant is provided through the injector, but such coolant flow is optional.
One issue that may arise during operation is crystallization of urea in the DEF, especially at the injector 222. Crystallization may occur, for example, when the DEF fluid is depressurized during system purge following engine shutdown. Specifically, when the DEF system is purged, pressure in the DEF conduits is reduced from an operating pressure value to a pressure close to atmospheric pressure. Given the relatively elevated temperature of the DEF injector 222 in this condition, and the pressure decrease, the boiling point of the solution is lowered, which in turn may cause water from the DEF solution to boil and evaporate. In certain conditions, the evaporated water may cause a super-saturated solution and/or solid urea crystals to form within the DEF injector. Such solids may have a particular melting temperature that can be predetermined and dependent on the chemical compounds or mixtures thereof that are prone to crystallization. Such crystallization may obstruct normal injector operation, for example, by physically blocking the opening of the injector valve and/or blocking DEF conduits within the injector that supply DEF to the valve for injection.
More specifically, the system 200 is packaged such that the position of the DEF injector 222 is relatively external to the surrounding structures and exposed to a convective cooling air flow both during operation of the engine as well as post-shutdown. In reference to
A controller 300 and various sensors are disposed to monitor and control operation of the system 200. More specifically, the system may include one or more temperature sensors disposed to measure exhaust temperature within the system 200 and provide temperature signals indicative of the temperatures measured to the controller 300. The controller 300 may be a single controller, as illustrated in
In this embodiment, the term “controller” is meant to include one, two, or more controllers that may be associated with the machine 100 and that may cooperate in controlling various functions and operations of the machine 100 (
The controller 300 is associated with the DEF injector via a DEF injector command line 301, through which the controller may monitor and control the injector 222. The controller 300 may further be associated with one or more temperature sensors disposed to measure exhaust temperature within the system 200. In the illustrated embodiment, a first temperature sensor 304 is connected to the controller 300 via a first temperature communication line 306. The first temperature sensor 304 provides a first temperature signal to the controller 300 that is indicative of a temperature of exhaust gas entering the after-treatment system 200 during operation. As shown, the first temperature sensor 304 is disposed downstream of a regeneration assistance device 308, for example, a “Cat Regeneration System” (CRS), which is available from Caterpillar, Inc. of Peoria, Ill., and/or a back pressure device. Back pressure devices are typically embodied as a valve such as a butterfly valve or a moveable variable nozzle turbine arrangement, which can be arranged to selectively block the exhaust conduit of an engine thus increasing exhaust back pressure on the engine and also increasing exhaust temperature. At present, the CRS in the illustrated embodiment is an active regeneration system used in engines rated 130-560 bkW (175-750 bhp) to selectively elevate exhaust gas temperatures to promote oxidation and burn off soot in the DPF 210, as required. The CRS includes a fuel-fired heater that generates a flame within the exhaust system of the machine to thus increase the temperature of exhaust gas that passes therethrough. Activation and control of the CRS 308 can be provided by the controller 300 through a CRS control line 310. In the illustrated embodiment, the controller 300 is further associated with a second temperature sensor 312, which is connected to the controller 300 via a second temperature communication line 314 through which the second temperature sensor 312 provides a second temperature signal to the controller 300 that is indicative of a temperature of exhaust gas entering the SCR portion of the system 200.
It should be appreciated that any known mode of heating the exhaust gas of the engine may be used in addition to or instead of the heating devices described above. For example, post injection of fuel to provide hydrocarbons in the exhaust, whether those hydrocarbons are injected directly into the exhaust conduit of the engine or provided in the engine cylinders in a late-post injection, may interact with various after-treatment components, such as a DPF, oxidize, and thus increase exhaust temperature selectively during engine operation.
An outline view of one embodiment for the DEF injector 222 is shown in
During normal operation, the injector 222 is generally protected from heat input to protect electronic and other components present therein from increased temperatures. To create a conductive heat transfer barrier between the body portion 230 and the exhaust system to which the injector 222 is connected to, a plurality of spacers 236 are used to space apart the body portion 230 from a mounting flange 238, thus creating a gap 240 between the body portion 230 of the injector 222 and the mounting flange 238.
DEF is supplied to the valve member 234 through the body portion 230. A DEF inlet conduit 242 is connected to a conduit 245 (
In reference now to
As mentioned above, when the DEF system purges DEF from the DEF injector, for example, the injector 222, while the injector is hot, the injector becomes susceptible to boiling of the water in the DEF solution within the injector. The boiling may increase the urea concentration of the DEF fluid, which can cause the precipitation and crystallization of urea deposits within the injector, thus possibly causing a partial or full blockage of the injector and preventing proper operation. Such effects are generally referred to herein as a “fault” or a “failure” condition relative to the DEF injector or to the DEF dispensing system in general. The melting point of urea solids under typical precipitation conditions can be as high as 130 deg. C. The controller 400 is advantageously configured to detect such conditions when they occur, and to remediate any decreases in operational capability of the DEF injector such that the cost and time otherwise required for repair or replacement of the injector and other system components can be avoided.
In one embodiment, the controller 400 may attempt to reestablish operation of the injector 222. In this operating mode, the controller may establish that a potential failure condition in the injector is imminent or expected before the failure is manifested or detected. To accomplish this, the controller 400 may monitor the exhaust temperature signal 402 during a DEF purge event to determine whether conditions favorable for urea crystal precipitation are present. The controller may further anticipate an exhaust temperature increase if a forced regeneration operation is forthcoming as indicated, for example, by the regeneration signal 404. The DEF purge event may be identified via the diagnostic signal 412, or via a combination of a particular set of engine speed RPM 408 and engine load 410 with an opening of the injector valve, as indicated by the injector valve position 406. When a DEF purge is underway or forthcoming in the presence of high exhaust temperatures, the controller may establish that a urea crystallization remediation should be carried out at the next available opportunity.
Alternatively, a urea crystallization condition within the injector may be diagnosed by a fault indication provided by a controller or control algorithm that monitors and operates the DEF injector. Specifically, the controller 400 may monitor operation of the DEF injector on an ongoing basis during operation. At times when urea crystals are impeding operation of the injector, a diagnosis of a fault at the injector may be carried out by comparing, within the controller 400, the position of the injector valve 406 with an expected or predetermined position of that valve based on a valve command. In other words, the controller 400 may command a valve opening for the injector valve to inject DEF fluid, and then monitor the injector valve position 406 to ensure that the valve has indeed opened to the degree requested. In the event that the valve does not fully respond to the commands, a fault condition may be indicated, a malfunction indication 416 may be provided, and a remediation process may be initiated to correct the fault condition, if possible. In one embodiment, the controller may compare a commanded DEF injector valve position with an actual DEF injector valve position that is determined based on a position signal provided by a position sensor associated with the DEF injector valve. Based on this information, the controller may determine that the fault is present when a difference between the commanded and actual DEF injector valve positions exceeds a predetermined threshold for a predetermined period.
When carrying out a remediation operation, the controller 400 may first ensure that the system is operating, i.e., pressurized DEF is present in the injector and DEF injections are performed on an intermittent basis in accordance with a DEF injector control strategy. The operating mode may be a normal operating mode, if the controller has previously determined that conditions promoting urea crystallization may have been present in the past, or may alternatively be an operating mode under a fault condition, if the controller has already determined a fault condition to be present that impedes normal DEF injector operation. Prior to a commanded DEF injection based on, for example, engine speed 408 and load 410 signals, the controller may first cause a heating of the injector 222 to a temperature between 100 and 140 deg. C, for example, a temperature around 130 deg. C, at least temporarily. Such temperature increase may be sufficient to melt any urea crystals that may be present therein. Upon melting, an injection may be carried out to evacuate the high-concentration urea solution from the injector, and then the injector may be returned to a normal, lower operating temperature.
Heating of the exhaust gas for this purpose may be accomplished by various methods, for example, by activation of a CRS, by causing an increased load on the engine, by using an exhaust back-pressure valve disposed in the exhaust system to restrict engine exhaust, thus increasing engine load and exhaust temperature, and/or by other methods or a combination of methods. Alternatively, the controller may passively monitor exhaust temperature during normal service for excursions above a threshold temperature, for example 130 deg. C. In such a passive or opportunistic remediation operation, the controller may active the injector if and when such higher exhaust temperature conditions are present to evacuate the now-melted urea from the injector.
An alternative embodiment of a controller 500 is shown in
More specifically, the DEF controller 502 is configured to receive various signals including, for example, engine speed 408, engine load 410, and injector valve position 406. On the basis of information provided by these signals, and other information such as tabulated data, the DEF controller provides an injector command signal 411. The DEF controller 502 also monitors DEF injection system operation and, in the event of a fault, provides a fault signal 416.
The command signal 411 is intercepted by the controller 500. During normal operation, i.e., in the absence of detected faults, the controller 500 may receive the injector command signal 411 and pass it through to the injector unaltered as an injector command 414. When a fault is detected, for example, when the fault signal 416, which is also provided to the controller 500, is activated, the controller 500 may attempt to remediate the fault as previously described. In such conditions, the controller 500 may take over operation of the DEF injector, for example, the injector 222 (
During operation under a failure remediation mode, the controller 500 may independently provide activation signals to the DEF injector, via the command signal 414, as well as cause other machine and/or engine systems to operate in a remediation mode, on the basis of information provided to the controller 500 by various input signals including exhaust temperature 402 and a time or event counter 412. As in the previously described embodiment relative to
When a fault condition is present, the controller 500 may first attempt to reestablish operation of the injector when the controller 500 determines that urea crystallization remediation should be carried out. When carrying out a remediation operation, the controller 500 may first ensure that the system is operating, i.e., pressurized DEF is present in the injector and DEF injections are performed on an intermittent basis in accordance with a DEF injector control strategy. The controller may cause a heating of the injector 222 to a temperature between 100 and 140 deg. C, for example, a temperature around 130 deg. C, at least temporarily. Such temperature increase may be sufficient to melt any urea crystals that may be present therein. Upon melting, an injection may be carried out to evacuate the high-concentration urea solution from the injector, and then the injector may be returned to a normal, lower operating temperature.
Heating of the exhaust gas for this purpose may be accomplished by various methods, for example, by activation of the CRS, by causing an increased load on the engine, by using the exhaust back-pressure valve disposed in the exhaust system to restrict engine exhaust, and/or by other methods or a combination of methods. Alternatively, the controller may passively monitor exhaust temperature during normal service for excursions above a threshold temperature, for example 130 deg. C. In such a passive or opportunistic remediation operation, the controller may active the injector if and when such higher exhaust temperature conditions are present to evacuate the now-melted urea from the injector.
The controller 500 may attempt to remediate a failure condition within a predetermined period following activation of the failure signal 416, for example, a period of about 1 hour. During this time, the failure signal 416 may retain active a warning system for the machine operator that the machine DEF injection system requires service. Within this time, the controller 500 may attempt to cause the machine to undergo a remediation cycle, which includes heating the injector, for example, by increasing exhaust temperature, and activating the heated injector to dispose of now-melted urea crystals that may be present therein. The controller 500 may attempt to complete one such full cycle during the 1-hour remediation period. If the remediation cycle is successful, the DEF controller 502 may regain normal system operation and deactivate the fault signal 416. If the remediation cycle is unsuccessful, the controller 500 may complete its remediation attempt without success and the fault signal 416 can remain active until the system is serviced. It is noted here that the DEF controller 502 may include active remediation functionality such as attempting to test system operation intermittently during a failure period.
The present disclosure is applicable to emission control systems for engines and, more particularly, to emission control systems using SCR processes requiring the injection of urea-based water solutions into engine exhaust streams. A flowchart for a method of remediating a fault in the urea injection components of such systems is shown in
In reference to
The remediation cycle includes checking whether a maximum remediation period has elapsed at 610 and, if it has, a failure flag is set at 624 and the process is terminated. While the remediation period is running, the exhaust temperature of the engine is progressively increased at 614. The temperature of the DEF injector is monitored and/or estimated at 616. While the injector is being heated, the injector is activated or cycled to evacuate any molted urea found therein at 618. Following injector activation, a functional test of the injector is carried out at 620 and, if the injector is functional, the exhaust temperature and thus the injector temperature is lowered at 622 towards a normal operating temperature and the process ends. If the failure remains, the exhaust heating and injector cycling procedures persist until the remediation period has elapsed at 610, at which time the failure flag is set at 624 and the process ends.
It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated.
Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.
