Urea solution pumps having leakage bypass

Urea solution pumps having leakage bypass flowpaths and methods of operating the same are disclosed. Certain embodiments are pump apparatuses including an inlet passage in flow communication with a source of urea solution and a pump chamber, an outlet passage in flow communication with the pump chamber and an exhaust after treatment system, a diaphragm facing the pump chamber and coupled with an actuator, a first housing member coupled with a second housing member form a seal around the pumping chamber, a leak collection chamber surrounding the seal, and a return passage in flow communication with the leak collection chamber and the inlet passage. Urea solution that leaks from the pump chamber past the seal is received by the leak collection chamber and flows through the return passage to the pump inlet passage.

BACKGROUND

Selective catalytic reduction (“SCR”) exhaust aftertreatment systems are an important technology for reducing NOx emissions from internal combustion engines such as diesel engines. SCR systems generally include a source of urea solution, a pump unit for pressurizing the urea solution, a metering unit for providing a controlled amount or rate of urea solution to an SCR catalyst, and an injector which provides urea solution to a urea decomposition region of an exhaust flowpath located upstream from an SCR catalyst. Many SCR systems also utilize pressurized gas to assist the flow of urea solution to the injector. While providing important reductions in NOx emissions, SCR systems suffer from a number of shortcomings and problems. Use of urea solutions in SCR systems may result in growth of urea crystals or deposits on various components of the system which may disrupt their operation. Injector nozzles may become blocked due to formation of urea deposits when urea solution is exposed to elevated temperatures. Such deposits may also form on the SCR catalyst or other components located in the exhaust flowpath or otherwise exposed to high temperatures. Leakage of urea to the ambient environment can damage or destroy other system components. There is a long felt need for advancements mitigating these and other shortcomings associated with SCR systems utilizing urea solution.

SUMMARY

Certain exemplary embodiments include pump apparatuses comprising an inlet passage in flow communication with a source of urea solution and a pump chamber, an outlet passage in flow communication with the pump chamber and an exhaust aftertreatment system, a diaphragm facing the pump chamber and coupled with an actuator, a first housing member coupled with a second housing member form a seal around the pumping chamber, a leak collection chamber surrounding the seal, and a return passage in flow communication with the leak collection chamber and the inlet passage. Urea solution that leaks from the pump chamber past the seal is received by the leak collection chamber and flows through the return passage to the pump inlet passage. Certain embodiments are methods including capturing urea solution that leaks from a pumping chamber and returning the leaked solution to the pump inlet. Further aspects, embodiments, forms, features, benefits, objects, and advantages shall become apparent from the detailed description and figures provided herewith.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

With reference toFIG. 1there is illustrated an exemplary system100for injection of urea solution into an SCR exhaust aftertreatment system. System100may be provided on a vehicle powered by an engine such as a diesel engine, or on an engine utilized in other applications such power generation or pumping systems. System100includes a pump134which draws urea solution from tank140through filter screen138and check valve136. A preferred urea solution is diesel exhaust fluid (DEF) which comprises a solution of 32.5% high purity urea and 67.5% deionized water. It shall be appreciated, however, that other urea solutions may also be utilized. In a preferred form pump134is a diaphragm pump, though it shall be appreciated that other types of pumps may be utilized. Pump134outputs pressurized urea solution at a predetermined pressure which flows through check valve130, pulsation dampener122, and filter124to provide pressurized urea solution to metering valve118. System100further includes a bypass valve128which is operable to open and close to permit or prevent the flow of urea solution through bypass line132to a location downstream of screen138where it may be returned to the tank140, for example, during a purging operation.

Metering valve118is operable to provide urea solution to blending chamber112at a controllable rate. Blending chamber112also receives a flow of pressurized air from an air supply102and discharges a combined flow of pressurized air and urea solution at outlet116. Air supply102may be integral to a vehicle, integral to an engine, or may be an air supply dedicated to system100. It shall be understood that additional embodiments may utilize pressurized gases other than air, for example, combinations of one or more inert gases.

Air supply102provides pressurized air to air regulator104. From air regulator104pressurized air proceeds to air shutoff valve106which can be selectably opened to allow pressurized air to flow to check valve110and closed to obstruct the flow of pressurized air. Check valve110opens when the air pressure at its inlet is above a threshold pressure and closes when the air pressure is below the threshold. From check valve110pressurized air flows to blending chamber112. A combined flow of aqueous urea solution entrained in pressurized air exits blending chamber outlet116and is provided to nozzle113which is configured to inject the combined flow into an exhaust aftertreatment system such as a urea decomposition tube or exhaust flow passage leading to an SCR catalyst.

System100may be controlled and monitored by a controller101such as an engine control module (ECM) or a doser control module (DCM). It shall be appreciated that the controller or control module may be provided in a variety of forms and configurations including one or more computing devices having non-transitory memory storing computer executable instructions, processing, and communication hardware. It shall be further appreciated that controller may be a single device or a distributed device, and the functions of the controller may be performed by hardware or software.

Controller101is operatively coupled with and configured to store instructions in a memory which are readable and executable by controller101to control diaphragm pump134, air shut off valve106, metering valve118, and bypass valve128. Controller101is also operatively coupled and may receive a signal from a pressure sensor114, pressure sensor120and temperature sensor126. Pressure sensor114is operable to provide a signal indicating the pressure in blending chamber112at a location downstream from the urea inlet and the pressurized air inlet. The pressure at this location may be pressure of a combined flow of pressurized air and urea, pressure of air alone, pressure of urea alone, or pressure in the absence of urea and compressed air depending on the operational state of metering valve118and air shut off valve106. Temperature sensor126is operable to provide a signal to controller101indicating the temperature of urea solution at a location between diaphragm pump134and metering valve118. Pressure sensor120is operable to provide a signal to controller101indicating the pressure of the urea solution upstream from of metering valve118.

With reference toFIG. 2there is illustrated an exemplary blending device200which is operable to output a combined flow of urea solution and pressurized air. Blending device200includes a metering valve202having an outlet203which provides urea solution to a blending chamber204. Metering valve can be controlled by controller101to provide urea solution at a controlled rate in a controlled amount. Blending chamber204also receives a flow of pressurized air from air passage205which extends from an outlet206to a seating surface208. The flow of pressurized air through air passage205is controlled to have a velocity and flow characteristics effective to provide an air curtain which resists crystal formation and migration. In the illustrated form, blending chamber204is a substantially cylindrical passage which is configured so that urea received from metering valve202is entrained in a flow of pressurized air received from air passage205, and a combined flow of pressurized air and urea solution is provided to outlet member230which is connected to an injector configured to provide the combined flow to an exhaust aftertreatment system. Pressure sensor207is operable to sense the pressure of the blended flow at a location downstream from urea outlet203and air outlet206.

The flow of pressurized air to air passage205is controlled by operation of check valve209and an upstream air shut off valve. Check valve209includes a closing member210which extends from a flexible diaphragm223in a direction toward a seating surface208. InFIG. 2closing member210is illustrated in a closed position in which it contacts seating surface208to form a seal and prevent flow from air supply passage222to air supply passage205. Biasing member214applies forge to plunger212which applies force to closing member210to maintain check valve209in the closed position. Biasing member214is illustrated in the form of a spring but may be a variety of other biasing members operable to provide force to closing member210in a direction toward seating surface208. Valve cover216contacts biasing member214and holds it in position relative to plunger212. Valve cover216also contacts diaphragm223and secures it to the underlying structure of blending device200.

The lower surface the diaphragm223is exposed to air supply passage222which receives pressurized air from air inlet220. The pressurized air in air supply passage222provides a force against the portions of the lower surface of diaphragm223and closing member210in contact with air supply passage222. This force opposes the force applied to closing member210by plunger212and biasing member214. When the force provided by pressurized air in air supply passage222is greater than the force provided by biasing member214check valve209opens and pressurized air flows from air supply passage222past check valve209to air passage205. The opening/closing threshold pressure is established by the pre-loading of biasing member214. The pre-loading of biasing member214is preferably tuned to provide rapid opening of check valve209at a pressure at or near a threshold pressure. The threshold pressure is preferably selected to be at or near the normal operating air pressure during urea injection, for example, 90% or more of the normal operating air pressure. This allows check valve209to open only when there is sufficient pressure for injection.

The threshold air pressure is also preferably selected so that check valve209opens only at or above a threshold air pressure which provides air flow characteristics effective to inhibit urea crystal growth in air supply passage205and urea crystal migration toward closing member210. The inventors have determined that for the illustrated embodiment an air flow velocity in air supply passage205of at least 47 m/sec. is effective to inhibit urea crystal growth in air supply passage205. The threshold air pressure may be selected to provide a margin of error on the minimum air flow rate, for example, the pressure may be selected to provide air flow velocity in air supply passage205of at least 50-55 m/sec. It should be appreciated, however, that the threshold air pressure should not exceed a magnitude where it would provides undesired air flow characteristics.

It shall be appreciated that the magnitude the threshold air pressure and associated air flow velocity effective to inhibit urea crystal growth may vary depending upon the characteristics of air supply passage205, check valve209and blending chamber204. In the illustrated embodiment air passage205extends over a length of about 6 mm and has a substantially constant diameter of about 1 mm. For this configuration a pressure of 3.45 bar gauge+/−0.4 bar gauge or greater has been determined to provide desired air flow characteristics effective to inhibit urea crystal growth. Additional embodiments include air supply passages with different characteristics and have different threshold air pressure values and associated air flow velocities effective to inhibit urea crystal growth.

With reference toFIG. 3there is illustrated an exploded sectional view of certain components illustrated inFIG. 2. Flexible diaphragm223includes a fold225that accommodates flexing to move closing member210and provides an alignment feature for plunger212. Flexible diaphragm further includes a peripheral ridge224which is contacted by housing to retain diaphragm223in position and provides an alignment feature for the housing216relative to the diaphragm223. A retaining clip226engages a groove227on plunger214to retain plunger and biasing member in place relative to housing216.FIG. 3illustrates closing member210in the form of a ball shaped or spheroid protrusion from diaphragm223. It shall be understood that additional embodiments include closing members in various other configurations, forms and shapes.

With reference toFIGS. 4A-4Dthere are illustrated detailed views of closing member210in various positions relative to seating surface208which illustrate the movement and deformation of closing member210during closing of valve209.FIG. 4Aillustrates closing member210in an open position relative to seating surface208. In the open position pressurized air is permitted to flow from air supply passage222between valve closing member210and seating surface208and to air passage205.FIG. 4Billustrates valve closing member210at the point during a valve closing event where valve closing member210first contacts seating surface208at location228.FIG. 4Cillustrates valve closing member210at a later point in the valve closing event. At this point valve closing member210has traveled across seating surface208effective to wipe an area229of seating surface208. During valve closing the closing member210slides across seating surface208and also elastomerically deforms to conform to the shape of seating surface208.FIG. 4Dillustrates valve closing member210in a fully closed position. Valve closing member210has slid across and wiped additional area230of seating surface208.

The interaction of closing member210with seating surface208provides a self-cleaning capability for check valve209. The sliding and wiping motion of closing member210across seating surface208is preferably effective to dislodge and wipe away urea crystals from seating surface208. The portion of closing member210that contacts seating surface208preferably has a hardness of 50-70 Shore A to allow sufficient elastomeric deformation but provide sufficient hardness to dislodge and wipe urea crystals from surface208. It shall be appreciated that other embodiments include closing members with different material properties that achieve a sliding and wiping of a seating surface with sufficient force to dislodge and wipe urea crystals from the seating surface.

With reference toFIG. 5there is illustrated a flow diagram of a wash cycle procedure240for a of a urea injection system. Procedure240begins at operation241in which a control routine for a urea injection system for an SCR exhaust aftertreatment system is initiated. From operation241, procedure240proceeds to operation242which interprets an engine key-on event. The operation to interpret an engine key-on event may include, additionally or alternatively, interpreting a communication or other parameter indicating that operations of the fluid injector are going to resume after a shutdown, or after a period of inactivity of a specified length that may not include a complete shutdown. If an engine system key-on event is interpreted to be true, procedure240proceeds to operation243. If an engine system key-on event is interpreted to be false, operation241repeats.

Operation243interprets a urea delivery request. The operation to interpret the urea delivery request includes a determination that urea injection for exhaust aftertreatment has been commanded or requested or that actual usage of the fluid injector is imminent. In certain embodiments, a command for the fluid injector to inject urea serves as the urea delivery request. If a urea delivery request is determined to be greater than zero, procedure240proceeds to operation244. If a urea delivery request is not determined to be greater than zero, operation243repeats.

Operation244commands an air shut off valve to close. The shut off valve may be, for example, valve106which is illustrated and described above in connection withFIG. 1. From operation244procedure240proceeds to timer evaluation245. Timer evaluation245is configured to evaluate whether a first predetermined time has elapsed. The first predetermined time is selected to ensure that an air flow passage has been sealed to prevent urea solution from flowing past the seal. In certain embodiments timer245is configured to account for the time required for a check valve positioned downstream from an air shut off valve to close such as is described above in connection withFIGS. 1-4. If timer evaluation245determines that the first predetermined time has not elapsed procedure240proceeds to operation246which increments the timer and returns to timer evaluation245

If timer evaluation245determines that the first predetermined time has elapsed procedure240proceeds to operation247which provides urea solution to a portion of the system to be washed. In certain embodiments urea is provided to a blending chamber such as blending chamber204illustrated and described above in connection withFIG. 2. In certain embodiments urea is provided at a rate effective to fill at least a portion of the blending chamber to dissolve or detach urea crystals which may have formed therein. In certain embodiments urea is provided at a rate effective to fill at least a portion of an air supply passage in flow communication with the blending chamber, such as air supply passage205illustrated and described above in connection withFIG. 2, to dissolve or urea crystals which may have formed therein. In certain embodiments urea solution is provided to substantially fill the blending chamber and the air supply passage.

From operation247procedure240proceeds to timer evaluation248which evaluates whether a second predetermined time period has elapsed. The second predetermined time is preferably a time that allows the urea crystals to dissolved or detach from the portion of the system provided with urea solution. The second predetermined time may be determined empirically through data sampling with a test fluid injector. In certain embodiments, the predetermined time may be a function of the urea flow rate during cleaning, the temperature of the supplied urea, a temperature of the fluid injector (e.g. from an ambient temperature or other estimate), and/or a function of the flow velocity or Reynolds number of the urea flowing within the fluid injector having a mixing passage of the given cross-section.

If timer evaluation248determines that the second predetermined time has not elapsed, procedure240proceeds to operation249which increments the timer and returns to operation247. If timer evaluation248determines that the second predetermined time has elapsed, procedure240proceeds to operation250which ends the wash cycle. In some embodiments procedure240may be repeated only once during a key on cycle. In other embodiments procedure240may repeat periodically or after a predetermined time has lapsed. In further embodiments procedure240may repeat when a system obstruction condition is detected.

Certain operations described herein include operations to interpret one or more parameters. Interpreting, as utilized herein, includes receiving values by any method known in the art, including at least receiving values from a datalink or network communication, receiving an electronic signal (e.g. a voltage, frequency, current, or PWM signal) indicative of the value, receiving a software parameter indicative of the value, reading the value from a memory location on a computer readable medium, receiving the value as a run-time parameter by any means known in the art, and/or by receiving a value by which the interpreted parameter can be calculated, and/or by referencing a default value that is interpreted to be the parameter value.

With reference toFIG. 6there is illustrated a flow diagram according to a further exemplary wash cycle procedure260for a urea injection system. Procedure260begins at conditional261which evaluates one or more initialization conditions. In certain embodiments the initialization conditions include evaluating whether a key-on value is true, a urea supply request is true, and a urea pump primed pressure check is true. If conditional261determines that the initialization conditions are not true, it repeats the evaluation of the one or more initialization conditions. If conditional261determines that the initialization conditions are true, it proceeds to operation262.

Operation262commands an air shut off valve to close. The air shut off valve may be, for example, air shutoff valve106illustrated and described above in connection withFIG. 1. From operation262procedure260proceeds to conditional263. Conditional263evaluates whether pressure information P1is less than a threshold pressure THP1. In an exemplary embodiment, pressure information P1is provided by pressure sensor207which is illustrated and described above in connection withFIG. 2. In other embodiments pressure information P1is provided by one or more pressure sensors positioned in other locations downstream from an air inlet and a urea inlet to a blending chamber. Threshold THP1is a threshold pressure identifying that a valve has closed to prevent the flow of pressurized air through a an air supply passage leading to the blending chamber. In an exemplary embodiment, threshold THP1is selected to indicate that check valve209has closed based upon an expected pressure value such as atmospheric pressure or a value greater than atmospheric pressure accounting for pressure seen at the outlet of the injection system such as 130 kPa. If conditional263is false it repeats the evaluation. If conditional263is true it proceeds to operation264.

Operation264performs a wash injection of urea solution into a blending chamber with an air shut off valve closed. In certain embodiments urea is provided to a blending chamber such as blending chamber204illustrated and described above in connection withFIG. 2. In certain embodiments urea is provided at a rate effective to fill at least a portion of the blending chamber to dissolve or detach urea crystals which may have formed therein. In certain embodiments urea is provided at a rate effective to fill at least a portion of an air supply passage in flow communication with the blending chamber, such as air supply passage205illustrated and described above in connection withFIG. 2, to dissolve or urea crystals which may have formed therein. In certain embodiments urea solution is provided to substantially fill the blending chamber and the air supply passage.

From operation264procedure260proceeds to conditional265. Conditional265is a timer which tests whether an elapsed time t1is greater than a time threshold THt1. The time threshold THt1is selected to allow the urea crystals to dissolved or detach from the portion of the system provided with urea solution. The time threshold THt1may be determined empirically through data sampling with a test fluid injector. In certain embodiments, the time threshold THt1may be a function of the urea flow rate during cleaning, the temperature of the supplied urea, a temperature of the fluid injector (e.g. from an ambient temperature or other estimate), and/or a function of the flow velocity or Reynolds number of the urea flowing within the fluid injector having a mixing passage of the given cross-section. If conditional265is false, it repeats. If conditional265is true, it proceeds to operation266.

Operation266opens the air shutoff valve and returns control of urea dosing to a control routine that provides urea solution at a rate needed for the SCR catalyst to reduce NOx generated by the engine which may be referred to as normal urea dosing operation. From operation266, procedure260proceeds to conditional267. In certain embodiments conditional267tests whether pressure P2is less than a pressure threshold THP2. In certain embodiments, pressure P2is the pressure sensed by pressure sensor207which is illustrated and described above in connection withFIG. 2, and pressure threshold THP2is a threshold which indicates a blockage upstream from pressure sensor207such as can occur through the accumulation or growth of urea crystals in blending chamber204. In certain embodiments conditional267also implements a timer which tests whether a time t2is greater than a time threshold THt2which indicates a minimum delay between sequential wash cycles. In certain embodiments conditional267evaluates whether either pressure P2is less than pressure threshold THP2or whether time t2is greater than time threshold THt2. In certain embodiments conditional267evaluates whether both pressure P2is less than pressure threshold THP2and time t2is greater than time threshold THt2. If conditional267is false, it repeats. If conditional267is true, it proceeds to operation262.

With reference toFIGS. 7A and 7Bthere is illustrated a flow diagram according to an exemplary wash cycle process270for a urea injection system which may be, for example, a system as illustrated and described in connection withFIGS. 1-4or another system. Process270begins an conditional271which evaluates whether initialization conditions are true. In the illustrated embodiment the initialization condition evaluation includes evaluating whether a key on condition is true indicating that an operator has turned a vehicle key on, and evaluating whether a urea pump prime complete condition is true indicating that a urea solution pump has successfully primed to provide urea solution pressure above an operation threshold, for example, urea solution pressure above 420 kPa. If the initialization conditions are not true conditional271repeats. If the initialization conditions are true process270proceeds to conditional272.

Conditional272evaluates whether an SCR system is ready. A number of criteria may be utilized to evaluate whether the SCR system is ready. In certain embodiments conditional272evaluates whether an SCR catalyst inlet temperature is within a predetermined temperature range, for example between 200° C. and 600° C., evaluates whether an SCR catalyst bed temperature is within a predetermined range, for example between 180° C. and 600° C., and evaluates whether an exhaust mass flow is above a predetermined value, for example, above 30 grams per second. These evaluations are effective to evaluate temperature and exhaust flow conditions associated with an injector nozzle that provides urea solution to an exhaust flowpath of the SCR system are in a range acceptable to avoid nozzle blockage due to insufficient temperature, excessive temperature, or insufficient exhaust flow. Additional embodiments utilize other criteria for determining whether the SCR system is ready including, for example, alternate temperature ranges, alternate flow rates, temperature measurements at alternate locations such as at or near the injector nozzle or a conduit in which the injector nozzle is disposed, exhaust temperature measurements, measurements by virtual sensors instead of or in addition physical sensors, as well as other criteria relating to SCR catalyst conditions, engine operation, and exhaust output of the engine. Certain embodiments evaluate whether the SCR system is ready based upon a receipt of a urea dosing command which is generated only when a separate routine has determined that the SCR system is ready and dosing can occur.

If conditional272determines that the SCR system is not ready, it repeats. If conditional272determines that the SCR system is ready, process270proceeds to operation273which performs a wash cycle which is illustrated and described in connection withFIG. 8. Operation273may also perform other wash cycle operations such as those described in connection withFIGS. 5 and 6. From operation273process270proceeds to operation274which starts a smart wash timer and initiates operation of a urea dosing system to provide urea solution at a rate needed for the SCR catalyst to reduce NOx generated by the engine which may be referred to as normal urea dosing operation.

From operation274process270proceeds to conditional275which evaluates whether the pressure of a combined flow of pressurized gas and urea is below a wash cycle threshold for a predetermined time, for example, less than 310 kPa for 10 seconds. If conditional275determines that the pressure of the combined flow is not less than the wash cycle threshold, it repeats. If conditional275determines that the pressure of the combined flow is below the wash cycle threshold for the predetermined time, process270proceeds to conditional276. Alternatively, in certain embodiments, if conditional275determines that the pressure of the combined flow is below the wash cycle threshold for the predetermined time, process270evaluates whether temperature of an SCR catalyst is below a threshold, for example, 400° C. If the temperature is at or below the threshold, process270proceeds to conditional276. If the temperature is above the threshold, process270proceeds to conditional281.

Conditional276evaluates whether the smart timer has reached a predetermined time limit. The predetermined time is selected to ensures that a wash cycle is not performed too frequently so as to negatively impact NOx conversion efficiency to an undesired or unacceptable degree or crate an undesirable or unacceptable increase the risk of injection nozzle blockage by urea deposits. If conditional276determines that the time limit has not been reached, it repeats. If conditional276determines that the time limit has been reached, process270proceeds to conditional281.

Conditional281evaluates whether a pressure of the combined flow of compressed gas and urea is less than an on-board diagnostic (OBD) threshold for predetermined time, for example, below 300 kPa for 10 seconds. If conditional281determines that the pressure of the combined flow is not below the diagnostic threshold for the predetermined time, process270returns to conditional275. If conditional281determines that the pressure of the combined flow is above the diagnostic threshold for the predetermined time, process270proceeds to conditional282.

Conditional282evaluates whether the SCR system is ready, for example, using the criteria described above in connection with conditional272, or other criteria indicating performance or operation of an SCR catalyst. If conditional282determines that the SCR system is not ready for operation, process270returns to conditional275. If procedure282determines that the SCR system is ready for operation, process270proceeds to operation283which sets a low pressure fault code which may indicate any of several failure modes including, insufficient pressure in an air supply tank due to a leak or a compressor malfunction, air shut-off valve malfunction preventing the valve from opening, air supply line blockage or leaks, urea crystallization obstruction or air flow, or other leaks, blockages or component failures associates with the air supply system. Certain embodiments may omit conditional282and proceed from conditional281to operation283.

If conditional276determines that the smart wash timer has reached the predetermined time threshold, process270proceeds to operation277which evaluates whether the SCR system is ready for operation, for example, as described in connection with conditional272, or by evaluating whether criteria indicating that the SCR aftertreatment system is ready for operation. If conditional277determines that the SCR system is not ready, it repeats. If conditional277determines that the SCR system is ready for operation, process270proceeds to operation278.

Operation278performs a wash cycle which is illustrated and described in connection withFIG. 8. Operation273may also perform other wash cycle operations such as those described in connection withFIGS. 5 and 6. From operation278process270proceeds to operation279. Operation279resumes normal dosing operation of the urea injection system. From operation279process270proceeds to conditional280which evaluates whether a pressure of the combined flow of urea solution and compressed gas is below a wash cycle threshold for a predetermined time, for example, less than 300 kPa for 20 seconds, less than 310 kPa for 20 seconds, or another predetermined time or pressure value. If conditional280determines that the pressure of the combined flow is not below the predetermined pressure for the predetermined time, process270proceeds to operation274if conditional280determines that the pressure of the combined flow is below the predetermined pressure for the predetermined time, process270proceeds to conditional276.

With reference toFIG. 8, there is illustrated a flow diagram according to an exemplary wash cycle273. Wash cycle273begins with operation291which closes an air shutoff valve and interrupts normal dosing operation to stop supplying urea solution. From operation291wash cycle273proceeds to conditional292. Conditional292evaluates whether an average pressure of a flow compressed gas is less than the predetermined pressure, for example 130 kPa or another predetermined pressure, and whether a timer is less than a predetermined time, for example less than 6 seconds or another predetermined time. If conditional292determines that the pressure of the combined flow is below the predetermined threshold and the timer is below the time threshold, wash cycle273proceeds to operation292which provides urea solution to a dosing system component such as a blending chamber at a predetermined rate for a predetermined time, for example, 0.8 ml per second for 3 seconds, 0.6 ml per second for 4 seconds, or another rate for another time effective to dissolve or detach urea crystals from the blending chamber or other portions of a urea solution injection system.

If conditional292determines that the pressure of the combined flow is not below the predetermined pressure or the timer is not less than the predetermined time, or both, wash cycle278proceeds to operation294which sets a fault code indicating a blocked injection nozzle. In certain embodiments, if conditional292determines that the pressure of the combined flow is not below the predetermined pressure or the timer is not less than the predetermined time, or both, wash cycle273waits a predetermined time, for example, 6 seconds, and proceeds to a conditional which evaluates whether an average pressure of a flow compressed gas is less than a second predetermined pressure threshold which may be the same as or different from the predetermined pressure of conditional292, for example 130 kPa, 150 kPa, or another predetermined pressure. If it is determined that the pressure is at or below the second threshold, wash cycle273proceeds to operation292. If it is determined that the pressure is above the second threshold wash cycle278proceeds to operation294.

In certain embodiments operation292provides urea to a blending chamber such as blending chamber204illustrated and described above in connection withFIG. 2. In certain embodiments urea is provided at a rate effective to fill at least a portion of the blending chamber to dissolve or detach urea crystals which may have formed therein. In certain embodiments urea is provided at a rate effective to fill at least a portion of an air supply passage in flow communication with the blending chamber, such as air supply passage205illustrated and described above in connection withFIG. 2, to dissolve or urea crystals which may have formed therein. In certain embodiments urea solution is provided to substantially fill the blending chamber and the air supply passage.

In certain embodiments wash cycle273may also perform a metering valve blockage diagnostic during operation292. During operation292urea pressure upstream from a urea metering valve is monitored. If a predetermined pressure drop is not observed, a fault code is set to indicate a metering valve blockage. Otherwise wash cycle273proceeds as described above. The metering valve blockage diagnostic may be performed during each wash cycle or only during the first wash cycle initiated after a key on event.

With reference toFIG. 9, there is illustrated an exemplary pump300for an exhaust aftertreatment urea injection system. Pump300includes a pump body302, a pump bonnet304and a pump head306which are coupled with threaded fasteners308. A flexible diaphragm is clamped between pump bonnet304and pump body302at a peripheral region of the diaphragm310. A surface of diaphragm310faces and defines a boundary of a compression chamber314. A seal is formed in the peripheral region where diaphragm310is clamped between pump bonnet304and pump body302. A diaphragm bead316positioned at the peripheral region of diaphragm310contributes to the formation of the seal. An annular leak collection chamber318surrounds the seal formed where pump bonnet304and pump body302clamp diaphragm310. The leak collection chamber318is sealed from the ambient environment by an sealing member320which in the illustrated embodiment is an O-ring positioned between and clamped by pump bonnet304and pump body302surrounding the leak collection chamber318. An actuator312is coupled with diaphragm310and is operable to move diaphragm310to vary the volume of compression chamber314.

During operation of pump300the actuator312drives the diaphragm310to alternately expand and contract the volume of compression chamber314. This operation creates a suction force at the pump inlet which draws urea solution from a urea supply source in the directions indicated by arrows331,332and334through inlet passage330. Urea solution is drawn through a check valve333which allows flow from the inlet passage330to chamber314but prevents flow in the opposite direction. While not illustrated, it should be understood that pump300also includes an outlet flow path in flow communication with chamber314and a second check valve that permits flow of pressurized urea solution from chamber314to the outlet flow path but not in the opposite direction. During operation of pump300pressurized urea solution is provided to the pump outlet.

During compression stroke actuator312moves diaphragm310to reduce the volume of chamber314. During the compression stroke the pressure of urea solution within chamber314may be sufficiently great so as to cause leakage through the seal formed by pump bonnet304and pump body302clamping diaphragm310. Solution that leaks past the seal is captured by the leak collection chamber318. Suction generated by the operation of pump300draws urea solution that is leaked into the leak collection chamber318through return passage322and into the inlet passage330where it returns to the inlet of chamber314. During operation of pump300, chamber314and return passage322are under substantially continuous suction. Thus, even if the seal formed by sealing member320is compromised, suction provided by operation of the pump300will draw air from the ambient environment to the pump inlet and will prevent urea solution from leaking to the ambient environment.

With reference toFIG. 10there is illustrated an exemplary exhaust flow path700for an SCR aftertreatment system. Exhaust flow path700includes an exhaust source702which may be a diesel engine for example. Exhaust source702provides a flow of exhaust through conduit730. A mixer720is disposed in the conduit730. An injection nozzle710is disposed in location downstream from the mixer720at or about the centerline of conduit730. The injection nozzle710injects urea in the direction of exhaust flow as indicated by spray712and the associated arrow. Spray712is distributed generally uniformly in the central region of flow path730but not distributed uniformly in the peripheral region of flow path730. Mixer720imparts a swirl in exhaust flowing through the peripheral region of conduit730while allowing flow to continue to proceed normally through the central portion of conduit730. In this manner exhaust back pressure is minimized by providing minimal instruction to obtain exhaust swirl only in the location where it is needed. The spray of urea solution712introduced into conduit730decomposes along the length of conduit730downstream from injection nozzle710to form ammonia. Ammonia is provided from outlet742to SCR catalyst750of catalyst unit740which functions to reduce emissions of NOx in the exhaust.

With reference toFIG. 11there is illustrated a detailed perspective view of mixer720. Mixer720includes a base portion729which can be attached to the interior surface of conduit730and a plurality of bent vanes720-728. The central region of the mixer is open to allow flow to proceed through the mixer without encountering vanes that impart swirl. Mixer720can be foamed from a stock sheet of metal which is cut, bent and rolled to the proper diameter to provide scalability for multiple exhaust conduit diameters. Swirl provided by mixer740is also scalable for a given exhaust conduit diameter by varying the number of swirl vanes and their geometries thereby reducing or increasing the delta pressure associated with the addition of mixer740, depending on the NOx reduction desired.

With reference toFIG. 12there is illustrated a graph of percent NOx conversion at different engine operating conditions for two different urea dosers with and without a mixer, as well as a conventional system baseline. The data ofFIG. 12illustrates that incremental improvements in NOx conversion are observed at each operational point with the inclusion of the mixer. It is further seen from the data inFIG. 12that greater improvements are observed at high space velocity values for the aftertreatment system utilized in the test.

A number of exemplary embodiments will now be further described. Certain exemplary embodiments comprise apparatuses for pumping urea solution to an exhaust aftertreatment system. Certain exemplary apparatuses comprise an inlet passage in flow communication with a source of urea solution and a pump chamber, an outlet passage in flow communication with the pump chamber and an exhaust aftertreatment system, a diaphragm facing the pump chamber and coupled with an actuator, a first housing member coupled with a second housing member form a seal around the pumping chamber, a leak collection chamber surrounding the seal, and a return passage in flow communication with the leak collection chamber and the inlet passage. Urea solution that leaks from the pump chamber past the seal is received by the leak collection chamber and flows through the return passage to the pump inlet passage. In certain forms the first housing member and the second housing member apply clamping force to a peripheral region of the diaphragm to form the seal. In certain forms suction is applied to the leak collection chamber during operation of the apparatus to pump urea solution to the exhaust aftertreatment system. Certain forms further comprise a second seal surrounding the leak collection chamber. In certain forms the second seal is formed by an o-ring disposed between the first housing member and the second housing member. Certain forms further comprise an inlet check valve configured to allow flow of urea solution from the inlet passage to the pump chamber and prevent flow of urea solution from the pump chamber to the inlet passage, and an outlet check valve configured to allow flow of urea solution from the pump chamber to the outlet passage and prevent flow of urea solution from the outlet passage to the pump chamber. In certain forms the exhaust aftertreatment system comprises an air-assisted urea solution injection nozzle configured to provide a combined flow of compressed air and urea solution to an exhaust flowpath.

Certain exemplary embodiments comprise methods of operating a urea solution pump of an exhaust aftertreatment system. Certain exemplary methods comprise providing a pump operable to receive urea solution from an inlet and provide urea solution to an outlet, the pump including pump chamber in flow communication with the inlet and the outlet, a seal surrounding the pump chamber, and a collection chamber surrounding the seal and in flow communication with the inlet, operating the pump to provide pressurized urea solution to the outlet, capturing urea solution that leaks past the seal in the collection chamber, and suctioning urea solution from the collection chamber through a return passage to the inlet. In certain forms the pump includes a diaphragm forming a boundary of the pump chamber and actuatable to expand and contact the volume of the pump chamber. In certain forms the seal is formed by a first housing member and a second housing member contacting opposing sides of a peripheral region of the diaphragm. In certain forms the first housing member and the second housing member apply clamping force to the peripheral region of the diaphragm effective to limit but not eliminate leakage of urea solution past the seal. Certain forms further comprise dissolving urea crystals formed in the return passage with leaked urea solution filling at least a portion of the return passage. In certain forms the capturing and suctioning are effective to eliminate leakage from the collection chamber to the ambient environment.

Certain exemplary embodiments comprise urea pump apparatuses for an SCR aftertreatment systems. Certain exemplary apparatuses comprise a compression chamber having an inlet and an outlet, an actuator configured to increase the volume of the compression chamber to draw urea solution through the inlet and decrease the volume of the compression chamber to expel urea solution from the outlet, a seal formed at a boundary of the compression chamber, and a chamber surrounding the seal and in flow communication with the inlet. Urea solution that leaks past the seal to the chamber is drawn to the inlet by suction force from the compression chamber. In certain forms the actuator is configured to drive a diaphragm to increase and decrease the volume of the compression chamber. In certain forms the seal is formed by clamping an annular region of the diaphragm. In certain forms the diaphragm is clamped by a pump housing containing the actuator and a pump bonnet defining the inlet and the outlet, and the chamber is an annular region defined by the pump housing and the pump bonnet. Certain forms further comprise a pump head defining a intake flow passage in fluid communication with the inlet and the chamber. In certain forms a second flow passage defined in the pump bonnet provides flow communication between the chamber and the intake flow passage. In certain forms urea crystals formed in the chamber or the second flow passage are dissolved by urea solution that leaks past the seal to fill a volume of the collection chamber or the second flow and contact the urea crystals.