Patent Application
20190376429
An exhaust system conducts hot exhaust gases generated by an engine through various exhaust components to reduce emissions such as nitrogen oxides NOx, for example. The exhaust system includes an injection system that injects fluid, for example ammonia, a diesel exhaust fluid (DEF), or a reducing agent such as a solution of urea and water, upstream of a selective catalytic reduction (SCR) catalyst. A mixer is positioned upstream of the SCR catalyst and mixes engine exhaust gases and products of the injected fluid. This mixture is then introduced into the SCR catalyst. The SCR converts the NOx, in the presence of the mixture of exhaust gas and injected fluid, into nitrogen and water. Under low temperature operating conditions, e.g. cold start and/or low flow conditions, this conversion becomes more difficult.
In one exemplary embodiment, a vehicle exhaust system includes a first exhaust after-treatment module that receives engine exhaust gases and a second exhaust after-treatment module that is downstream of the first exhaust after-treatment module. A valve is moveable between an open position that blocks flow to the first exhaust after-treatment module such that all exhaust gas flow bypasses the first exhaust after-treatment module and is directed into the second exhaust after-treatment module, a closed position that directs flow into the first exhaust after-treatment module before the flow enters the second exhaust after-treatment module, and a partially open position where one portion of flow is directed into the first exhaust after-treatment module and a remaining portion of flow is directed into the second exhaust after-treatment module. A controller controls movement of the valve between the open, closed, and partially open positions based on at least one of engine flow rate and NOx output.
In a further embodiment of the above, the controller controls movement of the valve based on exhaust gas temperature, engine flow rate, NOx output, or any combination thereof.
In a further embodiment of any of the above, the first exhaust after-treatment module includes at least a first ammonia source, a first mixing element, and a first SCR, and wherein the second exhaust after-treatment module includes at least a second ammonia source, a second mixing element, and a second SCR.
In a further embodiment of any of the above, the first exhaust after-treatment module is immediately downstream of the engine.
In a further embodiment of any of the above, the first SCR is smaller than the second SCR.
In a further embodiment of any of the above, the valve is only in the closed position during cold start or low flow conditions and wherein valve position is actively adjusted by the controller to vary the partially open position during high temperature and/or high flow conditions.
In another exemplary embodiment, a method of controlling a valve in a vehicle exhaust system includes controlling movement of the valve between the open, closed, and partially open positions based on at least one of engine flow rate and NOx output.
These and other features of this application will be best understood from the following specification and drawings, the following of which is a brief description.
In one example, the valve 22 is moveable between at least an open position, closed position, and a partially open and variable position. In the closed position the valve 22 directs flow F into the first exhaust after-treatment module 16 before the flow enters the second exhaust after-treatment module 20 as shown in
Any type of valve can be used to control the flow of the exhaust gas between the modules 16, 20. In one example, the valve 22 comprises a valve flap or disc body that is pivotally supported by and positioned to extend across a cross-sectional area of a pipe within which the valve 22 is mounted. The valve 22 can be biased via a spring or other similar element to the closed position. An actuator/controller 28 can be coupled to the valve to control movement thereof.
In one example, the controller 28 controls movement of the valve 22 between the open, closed, and partially open/variable positions based on at least one of engine flow rate and NOx output. At least one flow sensor 30 communicates engine flow information to the controller 28. At least one NOx sensor 32 communicates NOx output information to the controller 28. One or more temperatures sensors 34 communicate exhaust gas temperature information to the controller 28. The sensors 30, 32, 34 can be placed in any of various positions within the exhaust system 10 as needed dependent upon vehicle application, packaging space, etc. In one example, the controller 28 controls movement of the valve 22 based on engine flow rate and in another example, the controller 28 controls movement of the valve 22 based on NOx output. However, the controller 28 can control movement of the valve 22 based on exhaust gas temperature, engine flow rate, NOx output, or any combination thereof.
In one example, the first exhaust after-treatment module 16 includes at least a first ammonia source 40, a first mixing element 42, and a first selective catalytic reduction (SCR) catalyst 44, and the second exhaust after-treatment module 20 includes at least a second ammonia source 50, a second mixing element 52, and a second SCR 54. Other components, such as a particulate filter and/or a diesel oxidation catalyst (DOC) could also optionally be included in one or both of the modules 16, 20. In one example, the first exhaust after-treatment module 16 is immediately downstream of the engine 12.
In one example, the first 40 and second 50 ammonia sources are connected to an injection system 60 that is used to inject fluid such as ammonia, a diesel exhaust fluid (DEF), or a reducing agent such as a solution of urea and water, for example into the exhaust gas stream upstream from the first 44 and second 54 SCRs such that the respective first 42 and second 52 mixing elements can mix the injected fluid and exhaust gas thoroughly together. The injection system 60 includes a fluid supply 62, a doser 64, and a controller 66 that controls injection of the fluid as known. The controller 66 can be a separate controller from the controller 28 that controls the valve 22, or a common controller can be used. In this example, two separate injection systems 60 are shown for each of the first 16 and second 20 exhaust after-treatment modules; however, a single injection system 60 could be used for both exhaust after-treatment modules 16, 20. The advantage of using a separate injection system for each of the first 40 and second 50 ammonia sources is that two different types of fluid can be used if needed. The advantages of using a single system include a reduced number of components, reduced cost, and less packaging space is required.
In one example, the mixing elements 42, 52 comprise a mixer body with an internal mixing structure 48 such as one or more plates and/or baffles, which thoroughly mixes injected fluid with the exhaust gases and subsequently directs the mixture of engine exhaust gas and the injected fluid to the SCRs 44, 54. Any type of mixing element 42, 52 can be used in the modules 16, 20. Further, the ammonia source can be combined with the mixing element in a compact mixer configuration for vehicles with tight packaging constraints.
As discussed above, the first exhaust after-treatment module 16 is immediately downstream of the engine 12 in a close-coupled arrangement as shown in
The subject invention provides a valve 22, which is able to be opened at various angles throughout the engine operational range.
Thus, the subject invention provides a configuration where the variable control of the valve 22 gives continuous use of the close-coupled after-treatment module 16 while maintaining low pack pressure. The controller 28 controls the valve 22 via a program using an algorithm that is based on engine flow rate, or flow rate and temperature, or NOx output, or any combination of these characteristics. The controller 28 can include a processor, memory, and one or more input and/or output (I/O) device interface(s) that are communicatively coupled via a local interface. The local interface can include, for example but not limited to, one or more buses and/or other wired or wireless connections. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components.
The controller 28 may be a hardware device for executing software, particularly software stored in memory. The controller 28 can be a custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the computing device, a semiconductor based microprocessor (in the form of a microchip or chip set) or generally any device for executing software instructions. The memory can include any one or combination of volatile memory elements and/or nonvolatile memory elements as known.
The software in the memory may include one or more separate programs, each of which includes an ordered listing of executable instructions for implementing logical functions. A system component embodied as software may also be construed as a source program, executable program (object code), script, or any other entity comprising a set of instructions to be performed. The controller 28 can be configured to execute software stored within the memory, to communicate data to and from the memory, and to generally control operations of the computing device pursuant to the software. Software in memory, in whole or in part, is read by the processor, perhaps buffered within the processor, and then executed.
In one example, the peak gas flow from the engine 12 may be 1600 Kg/hr, with 9 g/KWhr NOx. The close-coupled after-treatment module 16 may only be able to accommodate 600 Kg/hr (limited by backpressure and SCR volume) so as the flow rate increased from 500 Kg/hr upward, the controller 28 would open the valve 22 proportional to the extra flow to maintain ˜550 Kg/hr through the close-coupled after-treatment module 16. With around 30% of the exhaust NOx treated by the close-coupled after-treatment module 16, when the treated and untreated gases merge and mix, the main after-treatment module 20 only has to treat the equivalent of 6 g/KW hr NOx, so the SCR substrates can be smaller, the ammonia introduced at the main after-treatment module 20 can be reduced, and the deposit risk (if using DEF) can be substantially reduced.
In the example shown in
Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
