Abstract:
Positive crankcase ventilation (PCV) systems have been employed on naturally-aspirated engines for over half a century. The gases in the crankcase exit the engine into the engine intake due to the slightly elevated pressure in the crankcase. Flow is controlled via a PCV valve in a PCV duct. In pressure-charged engines, PCV flow stops when pressure in the intake exceeds that of the crankcase. Such stagnation leads to sludging and deposit formation. According to an embodiment of the disclosure, reverse flow through the system is allowed by installing a second PCV valve in parallel with the normally-provided PCV valve, with the second PCV valve allowing an opposite direction of flow. Oil separators are provided on both PCV ducts to and from the engine to remove oil from blowby gases for flow in either direction.

Description:
FIELD 
       [0001]    The present disclosure relates to ventilating the crankcase of engines during boosted operation. 
       BACKGROUND 
       [0002]    Reciprocating, internal-combustion engines use piston rings so that combustion gases at high pressure in the cylinder do not readily escape to the crankcase. Some small fraction of the gases, less than 1% in a properly fitting piston-liner systems, does escape the combustion chamber past the rings and through the ring gaps. These gases are partially burned products of combustion that may contain unburned fuel and reactive components of partially burned fuel mixed with air. The very first emission control measure applied to automotive internal-combustion engines in the 1960s was a positive crankcase ventilation (PCV) system. Now such systems are universally employed. 
         [0003]    In  FIG. 1 , an engine system  100  with a PCV system is shown on a naturally-aspirated engine  102 . Engine  102  has a cylinder head  104  with a rocker arm cover (not separately shown) that covers the valvetrain components, a block  106 , and an oil pan  108 . Air is inducted to engine  102  via a duct  114  which has an air cleaner  110  and a throttle valve  112  that lead to an intake manifold  116 . Exhaust from engine  102  into an exhaust manifold  120  into an exhaust duct  122  that exhausts into the atmosphere after passing through any muffler and emission control apparatuses in exhaust duct  122 . 
         [0004]    Valvetrain components, which are not separately shown in  FIG. 1 , may include camshafts, rocker arms, roller finger followers, poppet valves, and springs. 
         [0005]    Engine  102  has a crankcase  108  into which blowby past engine rings exits. If these blowby gases were not vented, pressure would develop in the engine and would eventually find an escape route the atmosphere. As these gases venting from the crankcase account for about half of the hydrocarbon emissions from an engine that is without any emission control, clearly this is not an acceptable option. Crankcase  108  is in fluidic communication with volume within cylinder head  104  that is enclosed by a rocker arm cover. Blowby gases are drawn off through an opening in the rocker arm cover passing through a duct  130  with a PCV valve  132  disposed therein. Duct  130  fluidly connects the open space above the valvetrain components with intake duct  114  (downstream of throttle  112  and upstream of intake manifold  116 ). Pressure in duct  114  downstream of throttle  112  is at lower than atmospheric at almost all engine operating conditions. Thus, flow is induced via the pressure difference. PCV valve  132  controls flow through duct  130 . A clean air supply duct  134  for ventilation is provided between intake duct  114  at a location upstream of throttle  112  and couples to the rocker arm cover of cylinder head  104 . Duct  134  couples to cylinder head  104  at the opposite end at which duct  130  couples to flush the cylinder head with clean intake air. The PCV ducting shown in  FIG. 1  is one non-limiting example. 
         [0006]    An oil separator  136  is provided under the rocker arm cover. Blowby gases not only contain unburned hydrocarbons and corrosive components but also have oil mist that is thrown off rotating components in the crankcase and in the cylinder head that are provided pressurized lubricant. The oil contains phosphorous-containing additives that would deactivate a catalytic converter if allowed to burn in the combustion chamber. Even without the oil additives, it is preferable to keep the oil within the engine and prevent it from being inducted into the intake of the engine. Oil separator  136  is provided to extract the oil from the blowby gases prior to entering PCV valve  132  and then into intake duct  114 . Oil separator  136  may use cyclone separation by swirling the air so that the small droplets hit the walls of the separator and then drip back into cylinder head  104 . In some cases, oil separator  136  is a filter that collects the larger oil droplets, but allow gases to pass through. Captured oil eventually falls back into cylinder head  104 . Any suitable oil separation mechanism may be employed in separator  136 . 
         [0007]    Within an internal combustion engine there are various volumes: combustion chambers that are selectively coupled via poppet valve to intake ports and exhaust ports. There is a coolant system with pressurized coolant circulating mostly through the cylinder head and the upper portions of the cylinders. There are pressurized oil supply lines. An oil pump pulls oil out of the oil pan and pressurizes oil passages within the engine that feed bearing surfaces associated with moving parts. The oil leaks, in a controlled fashion, from between bearing surfaces or maybe sprayed onto parts such as piston skirts or the underside of pistons when they are oil cooled. The oil drips down to the oil pan. There is a volume in the engine, which includes the oil pan, the crankcase, and the valvetrain area in which gases and oil exists at mostly atmospheric pressure. These volumes, which is called oil-containment volume herein, are fluidly coupled. The oil-containment volume, within this disclosure, specifically excludes the pressurized oil lines which are oil only (no more than a small of incorporated air is in the oil) and is at much higher pressure than this oil-containment volume. 
         [0008]    In a boosted engine, such as one with a turbocharger or supercharger, pressure in duct  114  is often higher than pressure in crankcase  108 . In such a case, the flow would reverse, except the PCV valve  132  does have a shutoff that prevents reverse flow. If the boosted operation were momentary, the PCV system of the prior art would be suitable. However, the more drastic the downsizing/boosting of the engine, the greater the fraction of time that the engine spends in at a boosted condition, approaching 50% of the duty cycle of the engine in some cases. The problem that ensues is that without proper ventilation, sludge forms in the engine oil because of the higher contact with the corrosive byproducts of combustion. Sludge is a problem in its own right and also leads to varnish and deposits forming on engine components, e.g, the back of poppet valves, which degrades engine breathing (performance) and acts as an insulator on valves causing valve overheating and/or engine knock. Also, unburned fuel in the blowby dilutes the oil thereby reducing the oil&#39;s lubricating properties. Reverse flow cannot be allowed to occur as the oil laden blowby would be inducted into the engine and cause deposit problems in the engine as well as foul the catalyst with phosphorous from oil additives. 
       SUMMARY 
       [0009]    To overcome at least one problem in the prior art, a PCV valve system that allows reverse flow is disclosed. The engine has a cylinder block coupled to a cylinder head and an engine intake with a compressor and a throttle valve disposed therein. A first PCV duct fluidly couples an oil-containment volume within the engine and the engine intake downstream of the compressor. A PCV valve is disposed in the first PCV duct. The PCV valve allows flow when pressure in the engine intake is higher than pressure in the oil-containment volume. A second PCV duct fluidly coupling the engine intake upstream of the throttle valve and the oil-containment volume. The system further includes an oil separator fluidly coupled to the second PCV duct. The oil separator is located within the oil-containment volume. 
         [0010]    The cylinder block comprises a crankcase which has an oil pan coupled thereto. The cylinder head houses a valvetrain with a cover sealing the valvetrain volume. The oil-containment volume comprises volume within the crankcase, the oil pan, and the valvetrain in which oil and gases are housed. 
         [0011]    In some embodiments, the system further includes a third PCV duct fluidly coupling the an oil-containment volume within the engine and the engine intake downstream of the compressor and a second PCV valve disposed in the third PCV duct wherein the second PCV valve duct that allows flow when pressure in the engine intake lower than pressure in the oil-containment volume. 
         [0012]    The system further includes an oil separator fluidly coupled to the second PCV duct and located within the oil-containment volume. 
         [0013]    The PCV valve includes a housing defining an inlet and an outlet, a pintle valve with a taper that engages with the outlet, and a spring biasing the pintle valve toward the inlet. 
         [0014]    In an alternative embodiment, the valve has a housing defining a first opening and a second opening, a pintle valve having a first taper on a first end that engages with the first opening and a second taper on a second end that engages with the second opening, a first spring biasing the pintle toward the first end; and a second spring biasing the pintle toward the second end. 
         [0015]    Also disclosed is a ventilation system for an engine with an engine intake with a compressor disposed therein; a valve disposed in a first ventilation duct, which couples the engine intake downstream of the compressor with an oil-containment volume of the engine; and a second ventilation duct fluidly coupling the engine intake upstream of the compressor and the oil-containment volume. The valve closes when pressure in the oil-containment volume is higher than intake manifold pressure. The system has an oil separator disposed within the oil-containment volume and fluidly coupled to the second ventilation duct. 
         [0016]    The first ventilation duct couples to the oil-containment volume of the engine at a location distal from the location where the second ventilation duct couples to the oil-containment volume. 
         [0017]    The system may have both a first oil separator disposed within the oil-containment volume and fluidly coupled to the first ventilation duct and a second oil separator disposed within the oil-containment volume and fluidly coupled to the second ventilation duct. The first oil separator is displaced from the second oil separator such that gases in the oil-containment volume are thereby ventilated. 
         [0018]    The oil-containment volume comprises volumes within the engine in which unpressurized oil and gases reside including an oil pan, a crankcase, and a cylinder head coupled to the engine. 
         [0019]    Also disclosed is PCV system for an engine having an engine intake with a compressor disposed in the intake. A first duct with a valve disposed therein couples the engine intake downstream of the compressor with an oil-containment volume of the engine and a second duct coupling the oil-containment volume and the engine intake upstream of the compressor wherein the valve allows flow when pressure in the intake manifold exceeds pressure in the oil-containment volume. 
         [0020]    The system may further include a first oil separator disposed within the oil-containment volume and fluidly coupled to the first ventilation duct and a second oil separator disposed within the oil-containment volume and fluidly coupled to the second ventilation duct. The first oil separator is displaced from the second oil separator such that gases in the oil-containment volume are thereby ventilated when there is flow through the first and second ventilation ducts. 
         [0021]    The valve has a valve body having a first opening on a first end and a second opening on a second end; a pintle disposed within the body, the pintle having a first taper on a first end of the pintle that engages with the first opening and a second taper on a second end of the pintle that engages with the second opening; a first spring that biases the pintle toward the first end of the valve body; and a second spring that biases the pintle toward the second end of the valve body. 
         [0022]    Some embodiments include a third ventilation duct which couples the engine intake downstream of the compressor with an oil-containment volume of the engine and a second valve disposed in the third ventilation duct wherein the second valve closes when pressure in the oil-containment volume is lower than intake manifold pressure. 
         [0023]    The engine intake also has a throttle valve disposed therein and located upstream of the compressor. The first second duct couples to the engine intake upstream of the throttle valve. 
         [0024]    In embodiments in which the engine has a vee configuration with first and second cylinder heads, the first ventilation duct couples to the first cylinder head at a first end of the engine and the second ventilation duct couples to the second cylinder head at a second end of the engine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIGS. 1 and 5  are illustrations of prior art PCV systems system for naturally-aspirated in-line and vee engines, respectively; 
           [0026]      FIGS. 2 and 6  are illustrations of turbocharged in-line and vee engines, respectively, having PCV systems according to embodiments of the present invention; 
           [0027]      FIGS. 3 and 4  are PCV valve shown in cross section. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
         [0029]    One embodiment of a PCV system for an in-line, pressure-charge engine is shown in  FIG. 2 . An engine system  200  has an internal combustion engine  200  that has a cylinder head  204  coupled to an engine block  206  that has an oil pan coupled to block  208 . The crankcase is at the bottom of engine block  206  and is covered by oil pan  208 . Intake air is provided to engine  202  via an intake duct  218  into which an air cleaner  210 , a throttle valve  212 , and a compressor  216  are disposed. Exhaust leaves engine  202  via an intake manifold  220  through an exhaust duct  224  that has a turbine  222  disposed in exhaust duct  224 . Compressor  216  and turbine  222  are coupled to a shaft  248  forming a turbocharger. Energy in the exhaust gases drive turbine  222  which in turn drives compressor  216  to thereby pressurize the intake gases so that more work can be developed in engine  202 . The present disclosure also applies to engine with superchargers in which there is no turbine in the exhaust. The compressor in the intake is typically driven off the crankshaft of the engine via a transmission. 
         [0030]    A conventional PCV system is provided for providing ventilation when the pressure in the oil-containment volume of engine  202  is greater than the pressure in intake duct  218  (downstream of compressor  216 ). Such PCV system includes a first duct  230  that couples intake duct  218  with cylinder head  204  (in the oil-containment volume in cylinder head  204 ). A PCV valve is placed in first duct  230 . In the embodiment in  FIG. 2 , a part of the PCV duct that couples the two is part of a Y-duct  238  that is explained more completely below. A second PCV duct  234  couples the oil-containment volume in cylinder head  204  with intake duct  218  at a location upstream of throttle valve  212 . An oil separator  236  is housed within the oil-containment volume in cylinder head  204 . Oil separator  236  filters out oil droplets in gases in the oil-containment volume and returns them to the oil-containment volume, but lets the gases from the oil-containment volume pass through PCV valve  230 . The solid arrow in duct  230  and near duct  200  indicate the direction of flow in the normal PCV operation. 
         [0031]    The embodiment in  FIG. 2  also includes a reverse-flow PCV system. A second PCV duct  240  with a second PCV valve  242  provided therein couples intake duct  218  (at a location downstream of compressor  216 ) with the oil-containment volume within engine  202 . Part of the second duct is made up of Y-pipe  238 . Flow in the reverse PCV system moves in the direction shown by the dashed arrows shown near duct  234  and in  240 . An oil separator  246  is provided within the oil-containment volume in cylinder head  240  to remove oil mist and droplets from the gases moving into duct  234 . 
         [0032]    PCV valves  232  and  242  are shown in cross-section and in greater detail in  FIG. 3 . A housing of PCV valve  234  defines an inlet  258  and an outlet  254 . A pintle  256  has a squared off end proximate inlet  258 . When pressure is higher at outlet  254  than at inlet  258 , the squared off end of pintle  256  closes off inlet  258 . When pressure is higher at inlet  258 , pintle  256  moves toward outlet  254  thereby popping pintle  256  off inlet  258  and allowing flow through valve  234 . A spring  252  biases pintle  256  toward inlet  258 . As pressure at inlet  258  exceeds pressure at outlet  254  by an even greater degree, a tapered end of pintle  256  is pushed into outlet  254  and closes off the flow area, thereby controlling flow. PCV valve  242  is similar to PCV valve  232  except that it is an opposite direction. Desired flow characteristics of valve  242  may be different than that of valve  232  in which case, the taper of a pintle  276 , the taper of an outlet of outlet  274 , and spring tension of a spring  270  that biases pintle  276  toward inlet  278  can all be adjusted to provide such desired characteristics. Valve  232  is shown in a closed position in which inlet  258  is occluded preventing flow through valve  232 . Pintle  276  of valve  242  is shown lifted off the seat in the body of the valve so that flow can pass by pintle  276  through valve  242 . 
         [0033]    The embodiment in  FIG. 2  has two PCV valves  232  and  242  with more detail on valves  232  and  242  shown in  FIG. 3 . However, in an alternative in  FIG. 4 , a two-ended PCV  280  valve is provided in place of PCV valves  232  and  242 . Valve  280  can control flow in either of the situations where the pressure is higher at a first end than the second end or where the pressure is lower at the first end than the second end. Such a PCV valve  280  has a body that defines a first opening  292  and a tapered opening  296 . A pintle  282  has a first tapered end  290  that engages with opening  292  and a second tapered end  294  that engages with opening  296 . The tapers  290  and  294  can be selected to provide the desired flow characteristics in the forward (solid arrows) and reverse (dashed arrows) flow directions. A first spring  284  in valve  280  biases pintle  282  toward second opening  296  and a second spring  286  in valve  280  biases pintle  282  toward first opening  292 . Spring  284  is a stiffer spring than spring  286  in the embodiment in  FIG. 4 . 
         [0034]    Valves  232 ,  242 , and  280  show a tapered pintle with cylindrical openings. In alternative embodiments, the pintle ends could be cylindrical with openings  254 ,  258 ,  274 ,  278 ,  292 , and  296  in the bodies of valve  232 ,  242 , and  280  being tapered. In even another embodiment, both the openings  254 ,  258 ,  274 ,  278 ,  292 , and  296  and pintle ends are tapered, possibly with different taper angles so that the pintles move a great distance to provide a modest change in open area. This would provide very fine control of flow. 
         [0035]    A prior art PCV valve system is shown for a naturally-aspirated engine system  300  in  FIG. 5 . Engine  302  has a block  306  with an oil pan  308 . Block  306  has two cylinder banks and thus two cylinder heads  304  and  305 . Air is provided through air cleaner  320  into an intake duct  314  which has a throttle valve  312  therein and into an intake manifold  316 . A PCV system has a first duct  330  into which a PCV valve  332  is disposed and a second duct  334 . An oil separator  336  provided in the oil-containment volume within cylinder head  305  is fluidly coupled to one end of PCV duct  330  to remove oil mist before the gases are introduced into intake duct  314 . As described above in regards to an in-line engine, there is what is called herein as an oil-containment volume that is made up of volumes in the oil pan, the crankcase, and in the case of a vee engine, both cylinder heads  304  and  305 , specifically the volumes in which the valvetrains reside and specifically does not include the combustion chambers or any coolant volumes or pressurized oil passages. These volumes are in fluidic communication. To provide a true ventilation system where gases are pushed through the system, fresh air flows through duct  334  into cylinder head  304  at one end. Flow continues into oil pan  308  and then out of cylinder head  305  at the other end. The inlet and outlet for the ventilation system are purposely separated from each other. 
         [0036]    A disclosed embodiment of a PCV system for a pressure-charged engine system  400  is shown in  FIG. 6 . Engine  402  is a vee engine having an oil pan  408  coupled to a cylinder block  406  onto which two cylinder heads  404  and  405  are coupled. Air is provided to engine  402  via an air induction system that includes air cleaner  410 , a throttle valve  412  that controls flow of air through air intake duct  414  that is upstream of compressor  416 . Compressor  416  provides air into duct  418  that leads to intake manifold  419 . Engine  402  exhaust products of combustion into an exhaust manifold  420  into turbine  422 , which exhausts into exhaust duct  424 . In the forward-flow, or normal operation, gases and oil mist from within the engine (called oil-containment volume) that are mostly generated by blowby are provided into an oil separator  436  that leads to a PCV duct  435  that leads to following, in succession: a collector  437 , a PVC valve  432 , a collector  439 , a PCV duct  438 , and intake manifold  419 . Alternatively, PCV flow could be provided upstream of intake manifold  419 . To provide fresh air to make up for the gases drawn out through PCV valve  432 , a fresh air duct  434  fluidly couples intake duct  414  upstream of throttle valve  412  with oil-containment volume within engine  402 . Normal or forward PCV flow occurs when pressure in the oil-containment volume within engine  402  is greater than pressure in intake manifold  419  (or in intake duct  418 ). 
         [0037]    When pressure in the oil-containment volume with engine  402  is less than pressure intake manifold  419 , reverse PCV flow is induced. Gases from intake manifold  419  flow into PCV duct  438 , into collector  439 , through a PCV valve  440 , into collector  437 , into PCV duct  436 , into oil collector  436 , and into oil-containment volume in engine  402 . The gases are vented out through oil separator  446 , PCV duct  434  and on into intake duct  414  upstream of throttle valve  412 . 
         [0038]    Collector  436  is an alternative to Y-pipe  236  in  FIG. 2 . Collector  439  is an alternative to pipe  230  and  240  in  FIG. 2 . Depending on packaging and cost, one alternative may be found preferable over another. Another option is double PCV valve  280  that obviates collectors  437  and  439  as well as PCV valve  432  and  440 . 
         [0039]    To ventilate, the path through which the gases flow through the engine are made nearly as long as possible. Thus, the inlet and outlet are on opposite banks and opposite ends of the two banks. 
         [0040]    While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.