Abstract:
An exhaust aftertreatment system for an engine is provided that includes a burner, an air supply system and a control module. The air supply system may be in fluid communication with the burner and may include an air compressor disposed upstream from the burner. The air compressor may include a pump mechanism, a clutch assembly selectively transferring torque from the engine to the pump mechanism, and a motor selectively driving the pump mechanism. The control module may be in communication with the clutch assembly and the motor. The control module may selectively switch the air compressor between a first operating mode in which the clutch assembly transfers torque from the engine to the pump mechanism and a second operating mode in which the motor drives the pump mechanism.

Description:
FIELD 
     The present disclosure relates to a system for treating exhaust gases. More particularly, a compressor for an exhaust treatment system is discussed. 
     BACKGROUND 
     This section provides background information related to the present disclosure and is not necessarily prior art. 
     In an attempt to reduce the quantity of NO X  and particulate matter emitted to the atmosphere during internal combustion engine operation, a number of exhaust aftertreatment devices have been developed. A need for exhaust aftertreatment systems particularly arises when diesel combustion processes are implemented. Typical aftertreatment systems for diesel engine exhaust may include one or more of a diesel particulate filter (DPF), a selective catalytic reduction (SCR) system, a hydrocarbon (HC) injector, and a diesel oxidation catalyst (DOC). 
     During engine operation, the DPF traps soot emitted by the engine and reduces the emission of particulate matter (PM). Over time, the DPF becomes loaded and begins to clog. Periodic regeneration or oxidation of the trapped soot in the DPF is required for proper operation. To regenerate the DPF, relatively high exhaust temperatures in combination with an ample amount of oxygen in the exhaust stream are needed to oxidize the soot trapped in the filter. 
     The DOC is typically used to generate heat to regenerate the soot loaded DPF. When hydrocarbons (HC) are sprayed over the DOC at or above a specific light-off temperature, the HC will oxidize. This reaction is highly exothermic and the exhaust gases are heated during light-off. The heated exhaust gases are used to regenerate the DPF. 
     Under many engine operating conditions, however, the exhaust gas is not hot enough to achieve a DOC light-off temperature of approximately 300° C. As such, DPF regeneration does not passively occur. Furthermore, NO X  adsorbers and selective catalytic reduction systems typically require a minimum exhaust temperature to properly operate. Therefore, a burner may be provided to heat the exhaust stream upstream of the various aftertreatment devices to a suitable temperature to facilitate regeneration and efficient operation of the aftertreatment devices. 
     While air compressors have been associated with burners for exhaust treatment systems in the past, it may be beneficial to provide an improved air compressor to provide an appropriate amount of air flow to the burner under a variety of different engine operating conditions. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In one form, the present disclosure provides an exhaust aftertreatment system that may include an exhaust passageway, an exhaust aftertreatment device, a burner, an air supply system, and a control module. The exhaust passage may receive exhaust gas from an engine. The exhaust aftertreatment device may be disposed in the exhaust passage. The burner may be in a heat transfer relationship with the exhaust gas flowing through the exhaust passage upstream of the exhaust aftertreatment device. The air supply system may be in fluid communication with the burner and may include an air compressor disposed upstream from the burner. The air compressor may include a pump mechanism, a clutch assembly selectively transferring torque from the engine to the pump mechanism, and a motor selectively driving the pump mechanism. The control module may be in communication with the clutch assembly and the motor. The control module may selectively switch the air compressor between a first operating mode in which the clutch assembly transfers torque from the engine to the pump mechanism and a second operating mode in which the motor drives the pump mechanism. 
     The control module may switch the air compressor between the first and second operating modes based on a demand for airflow into the burner. Additionally or alternatively, the control module may switch the air compressor between the first and second operating modes based on a comparison of a power demand of the air compressor and a threshold capacity of the motor. 
     In another form, the present disclosure provides a method of controlling an air compressor for an exhaust aftertreatment system that may include determining a level of demand for airflow to a burner of the exhaust aftertreatment system. A level of power needed to power the air compressor to meet the level of demand may be determined. The method may also include determining whether the level of power is above a power threshold of a motor of the air compressor. The air compressor may be switched between a motor-driven operating mode and an engine-driven operating mode based on whether the level of power is above the power threshold and/or based on engine operating conditions. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a schematic representation of an engine and exhaust aftertreatment system according to the principles of the present disclosure; 
         FIG. 2  is a cross-sectional view of an air compressor of the exhaust aftertreatment system of  FIG. 1 ; and 
         FIG. 3  is a flow chart illustrating a method of operating the air compressor. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
       FIG. 1  depicts an exhaust gas aftertreatment system  10  for treating the exhaust output from an exemplary engine  12  to a main exhaust passageway  14 . An intake passage  16  is coupled to the engine  12  to provide combustion air thereto. A sprocket or pulley  18  may be directly or indirectly connected to a crankshaft  20  of the engine and may rotate with the crankshaft  20  during engine operation. A turbocharger  22  includes a driven member (not shown) positioned in an exhaust stream. During engine operation, the exhaust stream causes the driven member to rotate and provide compressed air to the intake passage  16  prior to entry into the engine  12 . It will be appreciated that the exhaust gas aftertreatment system  10  can also be used to treat exhaust output from a naturally aspirated engine or any other engine that does not include a turbocharger. 
     The exhaust gas aftertreatment system  10  may include a burner  26  that receives and burns fuel from a fuel delivery system  46  and air from an air delivery system  48 . The burner  26  is positioned downstream from the turbocharger  22  and upstream from a number of exhaust aftertreatment devices. The exhaust aftertreatment devices may include a hydrocarbon injector  28 , a diesel oxidation catalyst  30  and/or a diesel particulate filter  32 , for example. 
     The burner  26  may be positioned in a heat transfer relationship with exhaust gas flowing through the main exhaust passageway  14 . The burner  26  may be used to heat the exhaust gas passing through the main exhaust passageway  14  to an elevated temperature that will enhance the efficiency of the DOC  30  and allow regeneration of the DPF  32 . The burner  26  may also be operable to pre-heat one of more of the aftertreatment devices prior to ignition of the engine  12 . 
     The burner  26  may include a fuel inlet  40 , and air inlet  42  and an ignition device  44 . The fuel inlet  40  may receive fuel (such as diesel fuel, gasoline, compressed natural gas, or ethanol, for example) from the fuel delivery system  46 . The fuel delivery system  46  may include a fuel tank  50 , a fuel pump  52 , and a fuel supply line  54  coupled to the fuel inlet  40 . The air inlet  42  may receive air from the air delivery system  48 , which may include an air filter  56 , an air compressor  58 , and an air supply line  60  coupled to the air inlet  42 . The ignition device  44  may include an injector, a nozzle, a spark plug, a glow plug and/or any other suitable device(s) operable to ignite a combination of fuel and air received from the fuel inlet  40  and the air inlet  42 . 
     Referring now to  FIG. 2 , the air compressor  58  of the air delivery system  48  may include a housing  62 , a pump mechanism  64 , an electric motor  66  and a clutch assembly  68 . The air compressor  58  is arranged as a dual-input device. That is, the pump mechanism  64  may be driven by the electric motor  66 , the engine  12 , or a combination of these two power sources. The pump mechanism can be any suitable type of pump, such as a roots-type positive displacement pump, a screw pump, a rotary vane pump, a scroll pump, a reciprocating pump, a centrifugal pump, or any other type of pump. The housing  62  may define a chamber  70  including an air inlet  72  and an air outlet  74 . As shown in  FIG. 1 , the air inlet  72  may receive air from the air filter  56 . The air outlet  74  may discharge air to the burner  26  via the air supply line  60 . 
     In the particular embodiment illustrated in  FIG. 2 , the pump mechanism  64  includes first and second working members  76 ,  78 , first and second shafts  80 ,  82 , first and second bearing assemblies  84 ,  86 , and first and second gears  88 ,  90 . The first and second working members  76 ,  78  may be disposed within the chamber  70  of the housing  62  and may include a plurality of lobes  92 . Rotation of the first and second working members  76 ,  78  relative to each other causes air to be drawn into the chamber  70  through the air inlet  72  and force air out of the chamber  70  through the air outlet  74 . The first and second working members  76 ,  78  may be fixed to the first and second shafts  80 ,  82 , respectively, for rotation therewith. The first and second shafts  80 ,  82  may be rotatably supported by the first and second bearing assemblies  84 ,  86 , respectively. The first and second gears  88 ,  90  may be fixed to the first and second shafts  80 ,  82 , respectively, and may meshingly engage each other to cause rotation of the shafts  80 ,  82  at the same speeds and in opposite directions. 
     The motor  66  may be rated for operation up to a predetermined power threshold (e.g., a maximum power output or capacity). This threshold could be between about 1-1.5 kilowatts, for example. The motor  66  may be disposed within the housing  62  and may include a stator  94  and a rotor  96 . The stator  94  may be fixed relative to the housing  62  and may surround the rotor  96 . The rotor  96  may be fixed to the first shaft  80 . The stator  94  may include windings  98  in electrical communication with a battery  100 , a fuel cell and/or another electrical-energy-storage device. The motor  66  may include an inverter or a variable-frequency drive to achieve a wide range of speeds and power. When the windings  98  receive electrical current, the rotor  96  rotates relative to the stator  94 , thereby causing the first shaft  80  to rotate relative to the housing  62 . As described above, rotation of the one of the first and second shafts  80 ,  82  causes corresponding rotation of the other of the first and second shafts  80 ,  82  due to the engagement between the first and second gears  88 ,  90 . 
     The clutch assembly  68  may be of any suitable type or configuration. In the embodiment depicted in  FIG. 2 , the clutch assembly  68  may include a friction plate  102  and a pulley  104 . The friction plate  102  may be rotationally fixed to the second shaft  82 , yet axially movable relative to the second shaft  82  and the pulley  104 . The clutch assembly  68  may include a solenoid or other electromechanical actuator operable to move the friction plate axially relative to the pulley  104  between first and second positions. In the first position, the friction plate  102  may engage the pulley  104  to rotationally fix the pulley  104  relative to the friction plate  102  and the second shaft  82 . In the second position, the friction plate  102  may disengage the pulley  104  to rotationally decouple the pulley  104  from the friction plate  102  and the second shaft  82  such that the second pulley  104  and the second shaft  82  are free to rotate independently of each other. 
     The pulley  104  may be coupled to the pulley  18  (which is connected to the crankshaft  20  of the engine  12 , as shown in  FIG. 1 ) via a belt  106  or chain, for example. In this manner, operation of the engine  12  causes rotation of the pulley  104  at a speed that is proportional to the rotational speed of the crankshaft  20  of the engine  12 . That is, when the crankshaft  20  is rotating at a relatively low speed (e.g., during idling or low-load operating conditions), the pulley  104  may rotate at a relatively low speed. Conversely, when the crankshaft  20  is rotating at a relatively high speed (e.g., during acceleration or high-load operating conditions), the pulley  104  may rotate at a relatively high speed. Accordingly, when the friction plate  102  is engaging the pulley  104 , rotary motion of the crankshaft  20  is transmitted to the second shaft  82  to operate the pump mechanism  64 . 
     A control module  110  ( FIG. 1 ) is provided to monitor and control the flows of fuel and air through the fuel delivery system  46  and air delivery system  48 , respectively. The control module  110  may also monitor and control operation of the ignition device  44 . The control module  110  may include or be part of an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated or group) and/or memory (shared, dedicated or group) that execute one or more software or firmware programs, a combinational logic circuit and/or other suitable components that provide the described functionality. The control module  110  may be a part of or include a control unit controlling one or more other vehicle systems. Alternatively, the control module  110  may be a control unit dedicated to the exhaust gas aftertreatment system  10 . 
     As shown in  FIG. 1 , the control module  110  may be in communication with and control operation of the ignition device  44 , the fuel pump  52 , the motor  66  (via a motor drive unit  112 ) and the clutch assembly  68 . The control module  110  may also monitor operating conditions of the engine  12 , the burner  26 , and/or one or more of the aftertreatment devices  28 ,  30 ,  32 . Based on such operating conditions, the control module  110  may determine whether the air compressor  58  should be operated, at what speed or output capacity the air compressor  58  should be operated, and whether the pump mechanism  64  should be driven by the motor  66  or by the crankshaft  20  via the belt  106  and pulley  104 . 
     The motor  66  of the air compressor  58  may be designed to operate the pump mechanism  64  during periods of relatively low demand for airflow to the burner  26 . When the exhaust gas aftertreatment system  10  demands a relatively large amount of airflow to the burner  26  (i.e., an amount which requires more power to run the pump mechanism  64  that the motor  66  can effectively or efficiently produce), the control module  110  may cause the motor  66  to shut down and cause the clutch assembly  68  to rotationally couple the pulley  104  with the second shaft  82  so that the engine  12  can drive the pump mechanism  64 . 
       FIG. 3  illustrates an exemplary method of operating the air compressor  58 . At step  210 , the control module  110  may determine, based on operating conditions of the engine  12  and/or the exhaust gas aftertreatment system  10 , whether an amount of airflow to the burner  26  is needed that requires the air compressor  58  to be operated with more power than the threshold power of the motor  66 . If, the demand is below the threshold, the control module  110  may, at step  220 , cause the motor  66  to drive the pump mechanism  64  to supply air to the burner  26 . For example, the burner  26  may only need a relatively low amount of airflow under one or more of the following conditions: (1) when the engine  12  is idling or operating at relatively low engine-speeds with relatively low load; (2) during ignition of the burner  26  prior to start-up of the engine to pre-heat the aftertreatment devices; (3) between ignition events in the burner  26  to keep a small amount of air flowing through the burner  26  to reduce or prevent exhaust gas from entering the burner  26  and to reduce or prevent accumulation of fuel residue and combustion byproducts on components of the burner  26 . It will be appreciated that relatively low airflow demand may be desirable or may be sufficient under additional or alternative operating conditions. 
     When engine operating conditions create a demand for a relatively large amount of airflow to the burner  26  (such as, for example, when the engine  12  is operating at relatively high speeds and/or under relatively high loads), the control module  110  may, at step  230 , shutdown the motor  66  and engage the clutch assembly  68 . In some embodiments, before the motor  66  is shutdown and before the clutch assembly  68  is engaged, the control module  110  may adjust the speed of the motor  66  so that the first and second shafts  80 ,  82  are rotating at the same speed (or close to the same speed) as the belt  106  and pulley  104 . Once these speeds are matched or nearly matched, the control module may engage the clutch assembly  68  and shutdown the motor  66 . This may decrease wear on the clutch assembly  68  and reduce the driver&#39;s ability to perceive the change in load on the engine  12 . At step  240 , engagement of the clutch assembly  68  causes the pump mechanism  64  to be driven by the engine  12  via the belt  106  and pulley  104 . 
     At step  250 , the control module  110  may evaluate whether demand on the air compressor  58  is higher than the threshold operating capacity of the motor  66 . If the demand is higher than the threshold capacity, the control module  110  may maintain the clutch assembly  68  in the engaged position to continue driving the pump mechanism  64  with the engine  12 . When demand on the air compressor  58  drops to a level that is within the capacity threshold of the motor  66 , the control module  110  may disengage the clutch assembly  68  at step  260  and power-up the motor  66  to drive the pump mechanism  64  with the motor  66  at step  220 . 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.