Abstract:
A crankcase ventilation system may include a first exhaust flow path configured to permit flow of main exhaust gases from a combustion chamber of an internal combustion engine and a particulate trap disposed in the first exhaust flow path. The system may also include a second exhaust flow path configured to enable flow of crankcase gases from a crankcase of the internal combustion engine and to merge the crankcase gases with the main exhaust gases at a point in the first exhaust flow path located downstream of the particulate trap.

Description:
TECHNICAL FIELD 
   This disclosure is directed to an exhaust system for internal combustion engines and, more particularly, to a crankcase ventilation system for internal combustion engines. 
   BACKGROUND 
   In internal combustion engines, including diesel and gasoline engines, a fuel and air mixture is combusted in combustion cylinders. Reciprocating pistons in the combustion cylinders are moved between top dead center and bottom dead center positions by a crankshaft below the cylinders in a crankcase. As each piston moves toward its top dead center position, it compresses the fuel and air mixture in the combustion chamber above the piston. The compressed mixture combusts and expands, driving the piston downward toward its bottom dead center position. 
   Combustion in the cylinder releases energy and generates combustion products and by-products, most of which are exhausted from the cylinder into an exhaust system of the engine during the exhaust phase of the combustion cycle. However, some of the combustion products enter into the crankcase by blowing past seal rings around the pistons, and are thus termed “blow-by gases” or simply “blow-by.” Blow-by gases contain contaminants normally found in exhaust gases, such as, for example, hydrocarbons (HC), carbon monoxide (CO), NO x , soot, and unburned or partially burned fuel. In addition, because the crankcase is partially filled with lubricating oil being agitated at high temperatures, the blow-by gases may also contain oil droplets and oil vapor. 
   As blow-by gases build up in the crankcase, they must be vented to relieve pressure in the crankcase. Some systems vent the blow-by gases directly to the atmosphere. However, the contaminants in blow-by gases are harmful to the environment. Therefore, emissions concerns make direct atmospheric venting a poor option under most, if not all, operating conditions. 
   Normally aspirated engines have been developed that direct the crankcase gases back to the intake of the engine and mix them with the fuel and air mixture as it flows into the combustion chamber where the contaminants are mostly burned or oxidized during combustion. However, in an engine with forced induction, returning crankcase gases to the intake side of a compressor in a supercharger or turbocharger can result in fouling of the compressor wheel in a relatively short time period. Therefore, crankcase gases must undergo extensive purification before returning them to the intake in a supercharged or turbocharged engine. Further, even with extensive purification, some level of contamination may still exist that may be harmful to the supercharger or turbocharger or various engine components. 
   Systems have been developed for engines with forced induction that vent the crankcase gases to the atmosphere after the purification process, rather than introducing them back into the engine for further combustion and potentially fouling or otherwise inhibiting the performance of the supercharger or turbocharger. For example, U.S. Pat. No. 6,691,687, issued to Liang et al. on Feb. 17, 2004 (“Liang”), teaches a crankcase blow-by filtration system. In the system of Liang, crankcase gases are purified with a particle and droplet filter. These gases are heated parasitically via heat exchange with some of the main exhaust gases from the engine and also with an electrical heating element. These gases are further treated with a catalytic soot filter before being released to the atmosphere. 
   While the system of Liang successfully releases purified crankcase gases to the atmosphere, this system is complex. For example, the system of Liang includes multiple purification stages, additional structure for the parasitic heating, an additional energy source for the electrical heating element, and a catalytic filter dedicated to the crankcase gases. Each of these structures is separate from and in addition to the main exhaust path. 
   The disclosed control system is directed toward improvements and simplification of the system set forth above. 
   SUMMARY OF THE INVENTION 
   In one aspect, the present disclosure is directed to a crankcase ventilation system. The system may include a first exhaust flow path configured to permit flow of main exhaust gases from a combustion chamber of an internal combustion engine and a particulate trap disposed in the first exhaust flow path. The system may also include a second exhaust flow path configured to enable flow of crankcase gases from a crankcase of the internal combustion engine and to merge the crankcase gases with the main exhaust gases at a point in the first exhaust flow path located downstream of the particulate trap. 
   In another aspect, the present disclosure is directed to a crankcase ventilation system including a first exhaust flow path configured to permit flow of main exhaust gases from a combustion chamber of an internal combustion engine. The system may include a particulate trap disposed in the first exhaust flow path. The system may further include a second exhaust flow path configured to enable flow of crankcase gases from a crankcase of the internal combustion engine and to merge the crankcase gases with the main exhaust gases at a point in the first exhaust flow path located downstream of the particulate trap. The system may also include a first catalyst configured to catalyze the crankcase gases and a second catalyst configured to catalyze the main exhaust gases. In addition, the first catalyst may be heated. 
   In another aspect, the present disclosure is directed to a method for crankcase ventilation. The method may include venting crankcase gases from a crankcase of an internal combustion engine and routing the crankcase gases away from the crankcase in a first conduit. Exhaust gases from one or more combustion chambers of the internal combustion engine may be vented and routed away from the one or more combustion chambers in a second conduit. Particulates may be filtered from the exhaust gases with a particulate trap and crankcase gases may be merged with the filtered exhaust gases at a point downstream from the particulate trap. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic representation of a crankcase ventilation system according to an exemplary disclosed embodiment; and 
       FIG. 2  is a schematic representation of a crankcase ventilation system according to another exemplary disclosed embodiment. 
   

   DETAILED DESCRIPTION 
   Reference will now be made in detail to the drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     FIG. 1  illustrates an exemplary crankcase ventilation (CCV) system  10 . CCV system  10  may include an internal combustion engine  12 . Engine  12  may include combustion cylinders  14 , and may have intake and exhaust components attached to it, such as, for example, an air intake  16 , an intake manifold  18 , an exhaust manifold  20 , a main exhaust conduit  22 , and a CCV conduit  24 . 
   Engine  12  may be any kind of internal combustion engine. For example, engine  12  may be a gasoline engine or a diesel engine. Further, engine  12  may be naturally aspirated or may include forced induction such as turbocharging or supercharging. 
   CCV system  10  may include one or more exhaust treatment devices for reducing emissions in the exhaust gas from engine  12 . In particular, CCV system  10  may include a particulate trap  26  and an exhaust gas recirculation (EGR) system  28 , which may include an EGR conduit  30  and an EGR cooler  32 . 
   Particulate trap  26  may be any kind of exhaust filter configured to remove particulate matter, such as soot and/or ash, from exhaust gases. For example, particulate trap  26  may be a mesh, screen, etc. 
   Particulate trap  26  may also be catalytic. Alternatively, a catalytic unit, separate from particulate trap  26 , may be included to catalyze gases flowing through main exhaust conduit  22 . The catalyst used for a catalytic particulate trap  26  or a separate catalytic unit may be an oxidation catalyst, such as a diesel oxidation catalyst, configured to remove (i.e., oxidize) pollutants such as hydrocarbons (HC) and/or carbon monoxide (CO). Alternatively or in addition, a reduction catalyst may be included for removing (i.e., reducing) pollutants such as NO x . 
   CCV conduit  24  may be configured to direct the flow of crankcase gases ventilated from the crankcase of engine  12  (CCV gases) to main exhaust conduit  22  where the CCV gases may be merged with the main exhaust gases in main exhaust conduit  22 . CCV gases may be merged with the main exhaust at a location downstream from particulate trap  26 . Because the pressure of the exhaust gases in main exhaust conduit  22  downstream from particulate trap  26  may be lower than the pressures within the crankcase of engine  12 , CCV gases may flow from the crankcase to main exhaust conduit  22  without the aid of a pump. 
   CCV gases may be catalyzed before venting to the atmosphere. For example, CCV system  10  may include a separate CCV catalytic unit  34 , which may catalyze CCV gases prior to being released into the main exhaust flow in main exhaust conduit  22 . The catalyst used for a CCV catalytic unit  34  may be an oxidation catalyst configured to remove (i.e., oxidize) pollutants such as hydrocarbons (HC) and/or carbon monoxide (CO). Alternatively or in addition, a reduction catalyst may be included for removing (i.e., reducing) pollutants such as NO x . Further, CCV catalytic unit  34  may be configured to remove soluble organic fraction (SOF), which is primarily engine oil. 
   Because CCV gases may be cooler than desired for maintaining CCV catalytic unit  34  at a desired operating temperature (e.g., at least about 150 degrees Celsius), CCV system  10  may be configured to provide additional heating of CCV catalytic unit  34 . For example, CCV catalytic unit  34  may be heated parasitically from the heat of the main exhaust gases. In an exemplary embodiment, CCV catalytic unit  34  may be housed within main exhaust conduit  22 , as shown in  FIG. 1 . By housing CCV catalytic unit  34  within main exhaust conduit  22 , at least some of the heat from the exhaust gases in main exhaust conduit  22  may be transferred to CCV catalytic unit  34 . In this embodiment, CCV catalytic unit  34  may be maintained above a desired operating temperature without using an external heating device (e.g., an electrical heating element). In a similar configuration, CCV catalytic unit  34  may be disposed adjacent to main exhaust conduit  22  such that heat from the main exhaust gases is transferred to CCV catalytic unit  34 . 
   Alternatively, CCV catalytic unit  34  may be located away from main exhaust conduit  22 . In this configuration, a heating device  36  may be included to maintain CCV catalytic unit  34  at a desired operating temperature. Heating device  36  may be any type of heating device including, for example, electrical heating elements, burners, etc. Further, heating device  36  may be integral or non-integral with CCV catalytic unit  34 . 
   In lieu of or in addition to heating device  36 , CCV system  10  may include a pump  40  for compressing CCV gases. Compressing CCV gases will raise their temperature, and thus perform at least partially the function of heating device  36 . Compressed CCV gases may be held in a chamber  42  and released at a controlled rate to CCV catalytic unit  34 . 
   EGR system  28  may extract main exhaust gases from main exhaust conduit  22  and direct them back to air intake  16  where they may be reintroduced into the combustion chambers of engine  12 . By undergoing the combustion process again, more of the contaminants may be removed, thus reducing emissions further. Accordingly, the disclosed EGR system may also be referred to as clean exhaust induction (CEI). 
   Also, because exhaust gases typically have high temperatures, EGR system  28  may include EGR cooler  32  in order to avoid performance losses due to the lower amount of oxygen in hotter gases. EGR cooler  32  may cool EGR gases in any conventional manner to a lower temperature and thus a greater density. Higher density gases have higher levels of all gaseous components and thus more oxygen, which may increase performance of engine  12 . 
   In addition, EGR gases should be as clean as possible before recirculation to avoid damaging EGR cooler  32  and various engine components. Therefore, EGR conduit  30  may extract gases from a location downstream of particulate trap  26  and any catalytic unit not integral therewith. By doing so, the amount of particulates that may be reintroduced to engine  12  may be reduced. Also, EGR conduit  30  may extract gases from a location upstream from the point where the CCV gases are merged with the main exhaust gases in main exhaust conduit  22 . This may avoid recirculation of additional contaminants from CCV gases. 
     FIG. 2  illustrates an exemplary embodiment, wherein both the main exhaust gases and the CCV gases may be catalyzed by the same catalytic unit. As shown in  FIG. 2 , a catalytic unit  38  may be positioned downstream from the point where the CCV gases are merged with the main exhaust gases. EGR conduit  30  may extract gases from main exhaust conduit  22  downstream of catalytic unit  38 , in order to insure that the EGR gases are as clean as possible. 
   INDUSTRIAL APPLICABILITY 
   The disclosed crankcase ventilation system may be employed on any type of internal combustion engine to reduce overall emissions to the environment while extending the usable lifetime of engine and exhaust system components. By routing CCV gases to main exhaust conduit  22  rather than to air intake  16  or upstream of particulate trap  26 , the useable lifetimes of engine components, and particularly any turbochargers or superchargers that may be part of the engine&#39;s induction system, may be extended. Also, by routing the CCV gases downstream of particulate trap  26 , the usable lifetime of particulate trap  26  can be extended. Otherwise, if CCV gases were routed upstream of particulate trap  26 , over time, contaminants within the CCV gases, particularly oil vapor and droplets, may clog the particulate trap  26  or otherwise render it ineffective. 
   Further, by routing CCV gases downstream of particulate trap  26 , the ash service interval of particulate trap  26  may be extended. Engine oil, particularly for diesel engines, may contain a small amount of ash, which is used to enhance the lubricity of the oil. This ash can be present in exhaust gases. Because some exhaust gases blow by into the crankcase, CCV gases from the crankcase may also contain some of this ash. However, this ash may only be present in CCV gases in very small amounts, which are essentially immeasurable on a conventional emissions test. But, if CCV gases are directed into the main exhaust upstream from a particulate trap, over many miles of operation (e.g., 250,000 miles) this ash can build up on the particulate trap. Therefore, by routing the CCV gases downstream of particulate trap  26  the disclosed system may avoid contributing to ash buildup on particulate trap  26  without appreciably adding to the overall emissions of engine  12 . Accordingly, by avoiding additional ash buildup, particulate trap  26  may not need to be cleaned as frequently. 
   In addition, because the CCV gases may be routed downstream of particulate trap  26  where the pressure is relatively low, no pump is required to transport the gases from the crankcase to main exhaust conduit  22 . When CCV gases are routed upstream of a particle filter, a pump may be required because the particle filter can create back pressure in the main exhaust, which can be higher than that in the crankcase. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed crankcase ventilation system without departing from the scope of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and their equivalents.