Patent Application
20150260069
This disclosure relates generally to fluid delivery systems used in association with vehicles and, more particularly, to a fluid delivery system for diesel exhaust fluid for use with engine emission control systems.
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, diesel exhaust fluid (DEF), which may include urea or a urea-based water solution, is mixed with exhaust gas before being provided to an appropriate catalyst. In some applications, the DEF is injected directly into an exhaust passage through a specialized injector device. In the case of urea, the injected DEF 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 DEF sufficiently close to the engine system such that the engine can be continuously supplied during operation. Various DEF delivery systems are known and used in engine applications. In known DEF injection systems, a reservoir is installed onto a vehicle for containing the DEF, which is drawn from the reservoir and delivered in metered amounts to the engine exhaust system.
In most engine applications, a precise delivery of DEF is required to achieve a desired and sufficient abatement of undesirable exhaust constituents as well as to avoid frequent fluid replenishments. For example, a fluid flow that is below a desired rate, depending on engine operating conditions, may not sufficiently abate engine emissions. Similarly, a fluid flow that is above a desired rate may deplete fluid supply in the vehicle prematurely, which can lead to more frequent vehicle service and/or insufficient emissions abatement due to lack of fluid after the fluid has been prematurely depleted and before it can be replenished.
The disclosure describes, in one aspect, a fluid delivery system. The fluid delivery system includes a fluid reservoir adapted to enclose a fluid therewithin, the fluid reservoir comprising a reservoir body forming a reservoir volume that encloses the fluid therewithin and that includes a fluid draw conduit, which is configured to draw fluid from the reservoir volume, and a fluid return conduit, which is configured to return fluid to the reservoir volume. The fluid delivery system further includes a pump having an inlet fluidly connected to the fluid draw conduit such that the pump can draw fluid from the fluid reservoir, increase a pressure of the fluid to an operating pressure, and provide fluid at the operating pressure and at a desired fluid flow to a pressure line that is fluidly connected to an outlet of the pump. The fluid delivery system also includes a fluid injector fluidly in communication with the pressure line, the fluid injector configured to selectively open and allow pressurized fluid at a predetermined, injected fluid flow to pass therethrough when the fluid injector is open. A return orifice fluidly connecting the pressure line at a location downstream of the fluid injector with the fluid return conduit such that a return fluid flow is returned to the fluid reservoir can optionally be used, but is not required for all embodiments. A pressure regulator having a regulator inlet in fluid communication with the pressure line and a regulator outlet in fluid communication with the fluid return conduit is configured to provide a regulated fluid flow to the fluid reservoir when the operating pressure exceeds a pressure regulator opening pressure. During operation, the desired fluid flow is equal to a sum of the injected fluid flow, the return fluid flow and the regulated fluid flow.
In another aspect, the disclosure describes an exhaust after-treatment system for a machine. The system includes a diesel exhaust fluid (DEF) container adapted to enclose a DEF fluid therewithin. The DEF container comprises a reservoir body forming a reservoir volume that encloses the DEF and that includes a DEF draw conduit, which is configured to draw DEF from the reservoir volume, and a DEF return conduit, which is configured to return DEF to the reservoir volume. A DEF injector is configured to inject DEF from the container into an exhaust passage of an engine. A pump has an inlet fluidly connected to the DEF draw conduit such that the pump can draw DEF from the fluid reservoir and provide it at an operating pressure to the DEF injector through a pressure line. A return line has a return orifice and configured to return unused DEF from the DEF injector to the DEF container. A pressure regulator is configured to maintain a fluid pressure of the DEF provided to the DEF injector substantially constant by continuously shunting DEF from an outlet of the DEF pump to the DEF container. During operation, a DEF flow provided by the pump is equal to a DEF flow injected by the DEF injector, a second DEF flow returned to the DEF container, and a third DEF flow shunted to the DEF container by the pressure regulator.
In yet another aspect, the disclosure describes a method for operating a fluid system. The method includes drawing fluid from a reservoir with a pump, pressurizing the fluid with the pump to provide a desired fluid flow to a pressure line, circulating a return flow of fluid from the pressure line back to the reservoir through a return orifice continuously during operation, selectively injecting an injected flow of fluid from the pressure line through a fluid injector, shunting a regulated flow of fluid of fluid from the pressure line, and returning the regulated flow back to the reservoir continuously during operation, and adjusting, over a long term, the desired flow by comparing a pressure of fluid in the pressure line with a desired pressure. The desired flow is selected, based on environmental variables, and selectively set by appropriately commanding the pump. At all times during operation, the desired flow is equal to the sum of the return flow, the injected flow, and the regulated flow, not considering any leakage of fluid or other fluid loss from the system.
This disclosure relates to emission control systems for engines and, more particularly, to DEF metering and delivery systems for use with SCR-based after-treatment systems for diesel engines used on stationary or mobile machines. The machines contemplated in the present disclosure can be used in a variety of applications and environments. For example, any machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation, marine or any other industry known in the art is contemplated. For example, the type of machine contemplated herein may be an earth-moving machine, such as a wheel loader, excavator, dump truck, backhoe, material handler, locomotive, paver or the like. Apart from mobile machines, the machine contemplated may be a stationary or portable machine such as a generator set, an engine driving a gas compressor or pump, and the like. Moreover, the machine may include or be associated with work implements such as those utilized and employed for a variety of tasks, including, for example, loading, compacting, lifting, brushing, and include, for example, buckets, compactors, forked lifting devices, brushes, grapples, cutters, shears, blades, breakers/hammers, augers, and others.
The transfer conduit 112 fluidly interconnects the first module 104 with a second module 114 such that exhaust gas from the engine 102 may pass through the first and second modules 104 and 114 in series before being released at a stack 120 that is connected to the second module. In the illustrated embodiment, the second module 114 encloses a SCR catalyst 116 and an Ammonia Oxidation Catalyst (AMOX) 118. The SCR catalyst 116 and AMOX 118 operate to treat exhaust gas from the engine 102 in the presence of ammonia, which is provided after degradation of a urea-containing solution injected into the exhaust gas in the transfer conduit 112.
More specifically, a urea-containing water solution, which is commonly referred to as diesel exhaust fluid (DEF) 121, is injected into the transfer conduit 112 by a DEF injector 122. The DEF 121 is contained within a reservoir 128 and is provided to the DEF injector 122 by a pump 126. As the DEF 121 is injected into the transfer conduit 112, it mixes with exhaust gas passing therethrough and is carried to the second module 114. To promote mixing of DEF with exhaust, a mixer 124 may be disposed along the transfer conduit 112. The amount of DEF that may be injected into the transfer conduit 112 may be appropriately metered based on engine operating conditions. Accordingly, a desired amount of fluid at desired times may be provided to the transfer conduit 112 by the DEF delivery system.
As can be appreciated, the location of the DEF injector 122 on the transfer conduit 112 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. Alternatively, DEF may be used as a coolant medium.
A cross section of one embodiment for the urea container or delivery reservoir 128 is shown in
Fluid 420 may be drawn from the reservoir 200 via a draw line 424. The draw line 424 may dray fluid from the bottom of the reservoir 200 and be surrounded by a heater 426 that can effectively melt frozen DEF fluid under cold operating conditions such that liquid DEF can be provided at a supply outlet 427. The liquid DEF at the supply outlet 427 may be delivered to a pump, for example, the pump 126 shown in
A schematic of one embodiment for a fluid delivery system 300 is shown in
Pressurized fluid at the outlet of the pump 320 is provided to a pressure line 328. The pressure line 328 as shown in the illustrated embodiment includes a pressure junction 330 that provides, in parallel fluid circuit arrangement, fluid at pump pressure to a pressure regulator 332 and to a DEF injector 334, for example, the DEF injector 122 (
When fluid is injected from the injector 334, fluid pressure in the pressure line may decrease, especially if an appreciable amount of fluid is injected. Such pressure drop within the pressure line 328 will be indicated to the controller 326 by the sensor 324. In response, the controller 326 will command the motor 318 to activate the pump 320 to supply fluid into the pressure line 328 until the desired pressure is once again established in the pressure line 328. The initiation of the pump, however, as well as the activation and deactivation of the injector 334, typically causes pressure pulsations, for example, standing waves or a hydraulic pressure spike of fluid pressure within the pressure line 328. Such pressure fluctuations can interfere, at least temporarily, with the pressure signal readings from the sensor 324. Moreover, such pressure spikes may interfere with the calculations in the controller 326 of the amount of fluid injected through the injector 334 because such fluid pressure may be above or below the predetermined system pressure that exists under stable conditions within the pressure line 328. These and other effects in the system, which can cause instability and large fluctuations in system pressure, especially under conditions when high fluid amounts are being delivered therethrough in relatively quick succession during machine operation, which can ultimately lead to a greater or lesser fluid being provided through the injector 334 than what is desired.
To address such and other related fluid pressure issues, at least in part, the pressure regulator 332 is configured to, at least in part, mitigate high pressure spikes in the pressure line 328. As shown, the pressure regulator includes a valve element 340 that is biased in a closed position via a spring 342 and that, when open, fluidly bypasses the injector 334 by fluidly and directly connecting the pressure line 328 with the return line 338. Although a mechanical pressure regulator is shown, an electronic pressure regulator valve may alternatively be used, or a mechanical arrangement having a different configuration than the one shown in
These and other issues may be avoided by appropriately controlling the motor 318 with the controller 326 to drive the pump 320 such that an excess amount of fluid is provided to the pressure line 328. In one embodiment, the pump 320 is driven by the motor 318 at a predetermined speed and/or displacement, in general, at predetermined fluid flow rate, which exceeds the return flow into the reservoir 302 through the return orifice 336 and also causes the pressure regulator 332 to be in an open position even when the injector 334 is in a fully open condition. Stated differently, the pump 320 is driven to provide an excess fluid supply to the pressure line 328 that exceeds the maximum fluid flow demand of the system 300 by a predetermined about, for example, 10 or 15% above the maximum expected flow through the DEF injector when the fluid pressure in the system is at its maximum allowable value and the injector is fully open, i.e., when the injector duty cycle is at 100%. The fluid supply from the pump, therefore, is equal to the sum of fluid injected through the injector, fluid returned to the reservoir through the return orifice, and fluid shunted from the pressure regulator at all times during operation. Of course, this equality of fluid flows does not account for other fluid losses from the system such as leaks, evaporation and the like, or fluid stored in system components such as in the various conduits or within the fluid injector, which fluid storage may occur transiently and/or occur at system startup or shutdown but is otherwise stabilized during system operation.
The excessive fluid supply described above during stable system operation will not cause a concomitant fluid pressure increase in the pressure line 328 because of the action of the pressure regulator 332. In short, when the opening pressure of the pressure regulator 332 is selected to be about equal and, preferably, just below the desired fluid pressure under steady conditions within the pressure line 328, the excess fluid provided to the pressure line 328 will be shunted back to the reservoir 302 through the pressure regulator continuously during operation. In conditions when the injector 334 is open, the excess fluid flow provided by the pump 320 will account for the flow through the injector 334, the flow through the return orifice 336, and will also still cause the pressure regulator 332 to open, at least partially, to shunt fluid back to the reservoir 302. In this way, a stable pressure can be maintained at all times within the pressure line 328, and dampening that will reduce or eliminate pressure fluctuations within the pressure line 328 can be provided by a combination of the return orifice 336 and the flow through the pressure regulator 332.
To improve system control accuracy and avoid unnecessary wear on the pumping and other fluid elements of the system, the control scheme for the pump 314 operating within the controller 326 in the system 300 may account for various environmental and aging effects in the system. In one embodiment, the control algorithm, which provides a command to the motor 318 as an output, can include a closed-loop controller that is used to set the fluid flow rate of fluid provided through the pump 320 at a point that is just above the corresponding setting on the pressure regulator 332. In one contemplated embodiment, the closed-loop controller uses a feed-forward control term to set the initial pump speed to a predetermined pump speed that yields the desired fluid flow. The predetermined pump speed can be selected or set based on pump performance mapping and environmental conditions such as ambient temp, fluid temp, altitude and pressure setting of the pressure regulator. If such predetermined pump speed setting is considered as a base or normal operating condition, the control algorithm can also monitor system pressure and use a relatively long term feedback, for example, via an integral control term having a relatively large time constant, that is based on system pressure to slowly adapt and adjust the fluid flow rate through the pump and maintain predetermined and/or desired flow margin above a maximum flow consumption of the system. In this way, the pressure can automatically control overall system pressure.
A block diagram for a control 500 that controls the operation of the motor 318 and/or a displacement of the pump 320, as applicable to the system 300 as shown in
During operation, the controller 500 provides a motor/pump command signal 502, which as previously described may control the speed of a motor operating a pump and/or a displacement of a pump. In any case, the motor/pump command signal 502 is a signal that causes a change in a fluid flow provided to a pressure line of a fluid system such as the pressure line 328 in the system 300 (
The various environmental inputs, i.e., the ambient temperature 504, fluid temperature 506 and altitude 508 in the embodiment shown in
The desired system pressure 516 is provided to a summing junction 518, where it is compared to the system pressure 510. A pressure difference or error 520, which is indicative of a difference between the desired system pressure 516 and the actual, measured or estimated system pressure 510 that is present in the system, is provided to an integral function 522. The integral function, may be of the form shown in Equation 1 below:
where I(t) is the integral term over time (t), Ki is a constant, and e(τ) is a function that is integrated over a period (τ). As is known, integral terms can address residual steady-state error that can occur in systems. In this case, such errors may result from various sources such as sensor error, sensor creep, system aging, filter clogging, and other effects. In the illustrated embodiment, the pressure difference or error 520 may also be provided to a sentry function 524 that can provide a system fault signal 526 indicating that system service is required or that notifies the operator of a fault when the error 520 exceeds a maximum allowable error for a predetermined period.
The integral function 522 provides a correction signal 528 which passes through a delimiter 530. A delimited correction signal 532 and the desired system pressure 516 are provided to a summing junction 534 and are compounded to provide a corrected, desired system pressure in the form of the command signal 502. As can be appreciated, the desired system pressure 516, which can also be expressed as a desired system flow rate setpoint, is independent of fluid use by the system and only depends on fixed system parameters such as pump and motor operation and, optionally, on environmental parameters within which the system is operating. The flow and/or pressure setpoint provided by the determinator function 514 is independent of fluid use, which leads to an inherently stable control scheme. As previously discussed, flow changes within the system are addressed by the pressure regulator such that there is always a flow excess provided to the system. The steady-state error compensation provided by the integral function 522 addresses effects that may appear in the system over time and also helps diagnose system faults.
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. In the disclosed embodiments, a feed forward controller having a long-term feedback is used to create a control arrangement in which pressure fluctuations in the high-pressure DEF fluid delivery system are avoided. In one embodiment, the system sets a predetermined DEF flow which exceeds the maximum use of DEF by the injector such that an excess flow causes a pressure regulator to open, at all times, thus controlling the pressure continuously within the system.
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.
