Abstract:
A crankcase ventilation system for a turbocharged engine has full bi-directional flow for an idle state and a boosted state. A PCV valve provides air flow from the crankcase to the intake manifold in the idle state. A restriction in a first vent line limits fresh air into the crankcase in the idle state. A PCV bypass permits a one-way flow into the crankcase via a second vent line bypassing the PCV valve in the boosted state. A pressure relief valve in communication with the first vent line is configured to bypass the restriction in the boosted state when a pressure in the crankcase exceeds a threshold pressure. In a preferred embodiment, the PCV bypass is configured to bypass both the PCV valve and a pull separator (i.e., oil separator at the second vent line) in the boosted state.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates in general to crankcase ventilation for internal combustion engines, and, more specifically, to ventilation of a gasoline engine that employs a turbocharger for compressing the intake air at high engine loads. 
         [0004]    Gases accumulate in an engine crankcase when gases from engine cylinders bypass engine pistons and enter the crankcase during engine rotation. These gases are commonly referred to as blowby gases. The blowby gases can be combusted within engine cylinders to reduce engine hydrocarbon emissions using a positive crankcase ventilation (PCV) system which returns the blowby gases to the engine air intake and combusting the gases with a fresh air-fuel mixture. Combusting crankcase gases via the engine cylinders may require a motive force to move the crankcase gases from the engine crankcase to the engine air intake. One conventional way to provide motive force to move crankcase gases into the engine cylinders is to provide a conduit between the crankcase and a low pressure region (e.g., vacuum) of the engine intake manifold downstream of an engine throttle body. In addition, fresh air from a point upstream of the throttle body is added to the crankcase via a separate conduit (i.e., breather) to help flush the blowby products from the crankcase and into the intake manifold. 
         [0005]    Use of turbocharging with combustion engines is becoming increasingly prevalent. In an exhaust-gas turbocharger, for example, a compressor and a turbine are arranged on the same shaft (called a charger shaft) wherein a hot exhaust-gas flow supplied to the turbine expands within the turbine to release energy and cause the charger shaft to rotate. The charger shaft drives a compressor which is likewise arranged on the charger shaft. The compressor is connected in an air inlet duct between an air induction and filtering system and the engine intake manifold so that when the turbocharger is activated, the charge air supplied to the intake manifold and engine cylinders is compressed. 
         [0006]    Turbocharging increases the power of the internal combustion engine because a greater air mass is supplied to each cylinder. The fuel mass and the mean effective pressure are increased, thus improving volumetric power output. Accordingly, the engine displacement used for any particular vehicle can be downsized in order to operate with increased efficiency and reduced fuel use, wherein the turbocharger is inactive during times of low power requirements and is activated during times of high load, such as wide open throttle (WOT). In addition to reduced fuel consumption, turbocharging has a beneficial effect of reducing emissions of carbon dioxide and pollutants. 
         [0007]    Due to the increased pressure at the intake manifold during high load operation which results from compressing the inlet air by the turbocharger compressor, modifications to the conventional crankcase ventilation system are necessary. In particular, the high pressure introduced downstream of the compressor (e.g., in the intake manifold) could reverse the flow in the vent line thereby pressurizing the crankcase to an extent that could cause failure of the seals. To prevent such a reversal, a check valve is usually placed in that vent line. To avoid a buildup of blowby gas in the crankcase, the flow is allowed to reverse in the other vent line (i.e., the breather that otherwise supplies fresh air from a point upstream of the throttle body and turbocharger compressor into the crankcase). Thus, any pressure buildup in the crankcase that could damage the seals is prevented. 
         [0008]    During engine idling when a large vacuum is present at the intake manifold, it is desirable to maintain a negative pressure in the crankcase. To ensure a negative crankcase pressure at idle on a boosted gas (i.e., turbocharged) engine, it is often necessary to restrict the fresh air feed to the crankcase. An appropriately sized restriction in the corresponding breather vent line is used to accomplish this. However, if the crankcase fresh air feed is restricted too much then the crankcase may become positively pressurized under full load conditions (i.e., when the restricted vent line or breather reverses flow to evacuate the blowby gases into the low pressure section of the air inlet system), which can jeopardize the crankcase sealing integrity. It is often difficult or impossible to find a restriction level that provides the needed vacuum at idle while not creating an undesirably large positive pressure during full load operation. 
         [0009]    Copending U.S. application Ser. No. 14/525,554, filed Oct. 28, 2014, entitled “Crankcase Ventilation for Turbocharged Engine,” incorporated herein by reference, discloses a dual-acting valve having a first flow capacity into the crankcase and a second flow capacity out from the crankcase which is greater than the first flow capacity. The dual-acting valve provides the desired restriction when the engine is in an idle state and provides a greater flow when the engine is in a boosted state (i.e., when the turbocharger pressurizes the intake manifold) to avoid over-pressurization of the crankcase. In such a system, however, undiluted blowby gases are collected to be ingested by the engine. Oil degradation such as sludging, varnishing, and emulsification can occur due to insufficient fresh air being mixed with the blowby gases in the crankcase prior to reaching the oil separator. Undiluted blowby gases may accumulate high levels of unburned fuel, such as during a decel fuel cutoff, which may increase pollution or cause other problems. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention employs a PCV bypass which is sized to permit an appropriate flow of pressurized air during a boosted state from the intake manifold into the crankcase for diluting the blowby gases. The flow control components are arranged in a way that enables independent sizing of components and the ability to obtain desirable crankcase pressure under all operating conditions. 
         [0011]    In one aspect of the invention, a vehicle comprises an internal combustion engine with an intake manifold receiving fresh air via an inlet duct, wherein the engine includes a crankcase. A turbocharger has a compressor with an inlet coupled to the inlet duct and an outlet coupled to the intake manifold, wherein the engine and turbocharger have an idle state and a boosted state. A first vent line communicates between the crankcase and the compressor inlet. A second vent line communicates between the crankcase and the intake manifold. A PCV valve in communication with the second vent line is responsive to a vacuum pressure in the intake manifold to allow air flow from the crankcase to the intake manifold in the idle state. A restriction in communication with the first vent line is configured to limit a flow of fresh air via the first vent line into the crankcase in the idle state. A PCV bypass is configured to permit a one-way flow into the crankcase via the second vent line bypassing the PCV valve in the boosted state. A pressure relief valve in communication with the first vent line is configured to bypass the restriction in the boosted state when a pressure in the crankcase exceeds a threshold pressure. In a preferred embodiment, the PCV bypass is configured to bypass both the PCV valve and a pull separator (i.e., oil separator at the second vent line) in the boosted state. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  depicts a turbocharged internal combustion engine with a conventional crankcase ventilation arrangement. 
           [0013]      FIG. 2  depicts an improved ventilation system of the present invention with flow indicated during an idle state. 
           [0014]      FIG. 3  depicts an improved ventilation system of the present invention with flow indicated during a boosted state. 
           [0015]      FIG. 4  is cross-sectional views showing one embodiment of a push separator incorporating a flow restriction and a pressure relief. 
           [0016]      FIG. 5  is a cross-sectional view of one embodiment of a PCV bypass comprising a check valve. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0017]    Referring to  FIG. 1 , an internal combustion engine  10  in an automotive vehicle includes a plurality of cylinders. One cylinder is shown, which includes a combustion chamber  11  and cylinder walls  12  with piston  13  positioned therein and connected to crankshaft  14 . Combustion chamber  11  communicates with an intake manifold  15  and exhaust manifold  16  via respective intake and exhaust valves operated by respective cams. 
         [0018]    Engine  10  may preferably utilize direct fuel injection and an electronic distributorless ignition system as known in the art. Fresh outside air is conducted to engine  10  via an air filter  20 , a throttle body  21 , and an air inlet duct  22  connected to intake manifold  15 . Combustion products exiting exhaust manifold  16  are conducted via a conduit  23  to a catalytic converter  24  on their way to an exhaust system (not shown). A turbocharging system is comprised of a turbine  25  positioned in the exhaust gas flow before catalytic converter  24  and coupled to a compressor  26  by a driveshaft  27 . Exhaust gases passing through turbine  25  drive a rotor assembly which in turn rotates driveshaft  27 . In turn, driveshaft  27  rotates an impeller included in compressor  26  thereby increasing the density of the air delivered to combustion chamber  11 . In this way, the power output of the engine may be increased. One or more bypass valves (such as a wastegate) may be provided for turbine  25  and/or compressor  26  that are controlled in a desired manner to activate or deactivate turbocharging according to engine loading. 
         [0019]    Crankcase  30  refers to a crankcase volume that may be defined in part by an oil pan  31  and a cam cover  32 , for example. When an air-fuel mixture is combusted in engine combustion chamber  11 , a small portion of combusted gas may enter crankcase  30  through the piston rings. This gas is referred to as blowby gas. To prevent this untreated gas from being directly vented into the atmosphere, a positive crankcase ventilation (PCV) system is utilized which includes a first vent line (breather)  33  and a second vent line  34 . First vent line  33  is coupled between cam cover  32  and the low pressure side of compressor  26  such as at throttle body  21  (or alternatively at any other position along air inlet duct  22 ). Second vent line  34  is connected to crankcase  30  near oil pan  31  and to the high pressure side of compressor  26  (e.g., to intake manifold  15 ). Oil separators  35  and  37  are preferably included at the connections of vent lines  33  and  34  to crankcase  30  to remove entrained oil from any gases being returned to the engine air intake. 
         [0020]    During engine idling and low load conditions when turbocharger compressor  26  is not activated, a vacuum pressure in intake manifold  15  causes a crankcase ventilation flow in which fresh air enters crankcase  30  via first vent line  33  and leaves crankcase  30  via second vent line  34 . A one-way check valve  38  (e.g., a conventional PCV valve) in second vent line  34  allows flow in this direction. A restriction  36  in first vent line  36  has a size (i.e., flow capacity) that limits the amount of fresh air allowed to enter crankcase  30 , wherein the flow capacity is selected to maintain a desired vacuum pressure in crankcase  30  during the idle state. When compressor  26  is activated during a high load condition such as wide-open throttle, pressure in intake manifold  15  increases to a pressure higher than the pressure in crankcase  30 . Reverse flow in second vent line  34  is blocked by check valve  38 . Excessive accumulation of blowby gas in crankcase  30  is avoided by allowing a reverse flow in first vent line  33 . The sizing of restriction  36  has been a tradeoff between the desire to have a sufficiently small flow capacity during idle to maintain a desirable negative pressure in crankcase  30  (which would be lost if an unlimited amount of fresh air could enter via first vent line  33 ) and a desire to have a sufficiently large flow capacity during high engine load so that a high pressure buildup in crankcase  30  is avoided. As stated above, the lack of fresh air supply to the crankcase can lead to oil degradation and other issues. 
         [0021]    The invention introduces a supply of fresh air for ventilating a crankcase under all conditions, including an idle state and a boost state, for a vehicle system  40  shown in  FIG. 2 . An engine  41  includes a crankcase  42  which accumulates blowby gases  44  which enter crankcase  42  bypassing piston  43 . Fresh air enters inlet duct  45  and passes through a turbocharger compressor  46  past throttle  47  and into intake manifold  50 . 
         [0022]    A first vent line  51  communicates between crankcase  42  and inlet duct  45  via a push oil-air separator  54  and a restriction  53 . A pressure relief valve  55  is placed in parallel with restriction  53  between first vent line  51  and push separator  54 . A second vent line  52  is communicates between intake manifold  50  and crankcase  42  via a PCV valve  56  and a pull oil separator  57 . A PCV bypass  58  is configured to permit one-way flow into crankcase  42  via second vent line  52  bypassing PCV valve  56  in the boosted state. In a preferred embodiment, PCV bypass  58  also bypasses pull separator  57  which would otherwise introduce a large pressure drop that the relatively high flow rates seen under the boosted state. 
         [0023]      FIG. 2  shows PCV flow in the idle state of engine  41  which is driven by vacuum pressure in intake manifold  50 . Thus, fresh air flows via first vent line  51  through restriction  53  and push separator  54  into crankcase  42  for mixing with blowby gases  44 . The mixture flows through pull separator  57  and PCV valve  46  into intake manifold  50  for ingestion by engine  41 . The flow capacities for restriction  53 , pull separator  57 , and PCV valve  56  can be tailored for the idle state without making any significant trade-offs for the flow requirements for the boosted state. 
         [0024]    In the boosted state shown in  FIG. 3 , increased pressure in the intake manifold  50  drives a flow of fresh air via second vent line  52  through PCV bypass  58  and into crankcase  42 . The fresh air mixes with blowby gases  44 , and the mixture is extracted via push separator  54  into first vent line  51  and inlet duct  45 . As pressure in crankcase  42  initially rises above atmospheric pressure, the mixture flows through restriction  53 . As pressure in crankcase  42  builds further, pressure relief valve  55  opens to provide a bypass around restriction  53 , thereby limiting the positive pressure in crankcase  42 . In one preferred embodiment, pressure relief valve  55  is activated at a crankcase pressure of about 2.5 kPa. Relief valve  55  may be activated not only during a boosted state but may also provide a pressure relief in the event of engine backfire. Moreover, the flow capacities for PCV bypass  58 , push separator  54 , and pressure relief valve  55  can be tailored for the boosted state without making any significant trade-offs for the flow requirements for the idle state. Thus, the invention decouples the two sides of the ventilation system, allowing appropriate specification of the parameters for each system component for its specific purpose and enabling complete control of crankcase pressure under all operating conditions. 
         [0025]      FIG. 4  shows another embodiment for the restriction and pressure relief components in the first vent line. This embodiment employs a dual-acting valve having a flow capacity which varies depending upon the direction of air flow in order to simultaneously obtain optimized performance for limiting the inflow of fresh air during engine idling and fully venting blowby gas during high engine load. Air-oil separator  60 , which may be integrated with a cam cover, includes an inlet  61  for connecting to the first vent line, an outlet  62  for connecting to the crankcase, and plurality of internal baffles  63  which collect oil and return it to the crankcase via drains  64 . A sealing wall  65  partitions oil separator  60  into two separate chambers which are selectably coupled by dual-acting valve  66 . Valve  66  includes a large opening  68  in sealing wall  65  which is configured to provide a large flow capacity during blowby flow from the crankcase. A movable flap  68  is arranged to cover opening  67  and has a smaller orifice  69  aligned with opening  60  configured to provide a smaller flow capacity for fresh air flowing in the direction into the crankcase. Movable flap  68  is coupled at a pivot point to sealing wall  65  by a fastening pin. Movable flap  68  may preferably be comprised of a flat spring formed of sheet metal or other material that naturally returns to a flat configuration against opening  67  as shown in  FIG. 4 . 
         [0026]      FIG. 5  shows an embodiment of a PCV bypass comprising a check valve  70 . A valve body  71  includes an opening  72  with a valve seat  73  for receiving a plunger  74  which is normally disposed against seat  73  by a spring  75 . During the boosted state, a reverse PCV flow indicated by arrow  76  lifts plunger  74  off from valve seat  73  to provide a desired flow capacity for providing fresh air into the crankcase. Valve body  71  is adaptable for use as a separate device connected in a vent line or as an integral device formed with a connector, for example.