Abstract:
Cylinders of an internal combustion engine are provided with an exhaust port that is opened when the piston approaches bottom dead center. Exhaust in the cylinder at the end of the power stroke flows to an EGR tank for containment and cooling. During the intake stroke as the piston approaches bottom dead center, the exhaust port is reopened allowing gas from the EGR tank to flow into the cylinder as a portion of the charge prior to compression. Alternatively, the exhaust port on a first cylinder is connected to the exhaust port on a second cylinder to allow exhaust gas from the power stroke on the first cylinder to flow into the intake stroke on the second cylinder. Pulsed turbocharger systems comprise an internal combustion engine comprising a piston cylinder and a piston slidably disposed within the cylinder. The cylinder includes an exhaust gas port that is disposed through a wall section of the cylinder. The exhaust gas port is positioned near a bottom portion of the cylinder such that: (1) an opening of the port is exposed when the piston is at the bottom of its stroke within the cylinder; and (2) an opening of the port is covered when the piston is moved towards the top of its stroke. A turbocharger that is connected to the engine and comprises a turbine wheel that is in exhaust gas flow communication with the exhaust gas port. Pulsed exhaust gas exits the piston cylinder through the exhaust port, when the piston is near a bottom portion of its work stroke. This pulsed exhaust gas is directed to the turbine wheel to cause the turbocharger to produce boost air for directing to the engine.

Description:
RELATED APPLICATIONS 
   This application claims priority of U.S. Provisional Patent applications Nos. 60/416,054 and 60/416,169, both filed on Oct. 4, 2002. 

   FIELD OF THE INVENTION 
   This invention relates generally to the field of gasoline and diesel-powered internal combustion engine exhaust gas recirculation (EGR) systems for emission improvement and, more particularly, to an EGR gas system that receives, stores, and transmits exhaust gas directly through a port in a piston cylinder. This invention relates generally to the field of turbocharged gasoline and diesel-powered internal combustion engines and, more particularly, to a pulse only turbocharger system 
   BACKGROUND OF THE INVENTION 
   EGR is a known method for reducing NO x  emissions in internal combustion engines. A conventional EGR system works by taking a by-pass stream of engine exhaust gas from an engine exhaust manifold and pressurizing the exhaust gas a desired amount for injection into the engine&#39;s induction system, mixing with the intake air and combustion fuel mixture, and for subsequent combustion. A control valve is used within the EGR system to regulate the amount of exhaust gas that is routed to the engine induction system based on engine demand. The process of recirculating the exhaust gas insures that partially oxidized NO x  become fully oxidized, thereby reducing smog producing partially-oxidized NO x  emissions. Accordingly, such a conventional EGR system typically comprises exhaust by-pass tubing, related plumbing and manifolding, an engine crankshaft-driven EGR pump, and an EGR control valve, all of which are ancillary components that are attached to the engine. 
   A disadvantage of such conventional EGR systems is that they require the use of ancillary moving components, e.g., a pump and control valve, that are capable of failing or otherwise not performing properly, thereby interfering with the effective reduction of NO x . Additionally, these components must be attached externally the engine, thereby occupying space within an engine compartment. 
   It is, therefore, desirable that an EGR system be constructed that does not depend on the use of such external and ancillary moving parts. It is also desirable that such EGR system provide a level of NO x  reduction that is equal to or better than that provided by conventional EGR systems. 
   Turbochargers for gasoline and diesel internal combustion engines are known devices used in the art for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed via an exhaust manifold or exhaust pipe into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. 
   The exhaust gas routed to such turbocharger is a by-pass stream taken from the combined exhaust stream generated by the engine, e.g., from an exhaust manifold or exhaust pipe that combines the different exhaust gas streams leaving each engine cylinder. Accordingly, the exhaust gas routed to such a turbocharger passes to the turbocharger at a substantially unpulsed or continuous volumetric flow rate. Of course the amount of exhaust gas flow routed to the turbocharger will increase with increasing engine speed or rpm. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the exhaust housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber. 
   The amount by which the intake air is boosted or pressurized is controlled by regulating the amount of exhaust gas that is passed through the turbine housing by a wastegate valve. The wastegate valve is actuated, during turbocharger operation when the boost pressure is approaching a maximum desired pressure, to divert an amount of exhaust gas away from the turbocharger turbine housing to reduce the rotational speed of the turbine and, thereby reduce both the rotational speed of the air compressor and the amount by which the intake air is pressurized. 
   The above-described conventional turbocharger system is driven by a substantially continuous pressure exhaust by-pass stream from the engine exhaust. In such a system, the backpressure of the turbocharger can cause the exhaust pressure within the upstream exhaust system to be increased, ultimately robbing pumping energy from the engine crankshaft. Thus, although such a turbocharger functions to increase the boost pressure and combustion energy within the engine, it does so at a cost of increased backpressure. 
   It is, therefore, desirable that a turbocharger system be constructed that provides increased intake air boost pressure without significantly increasing the exhaust backpressure within the engine. It is also desired that such turbocharger system be capable of maintaining a positive pressure difference across an engine cylinder head at all operating points to both provide improved engine output and improved overall pumping efficiency. 
   SUMMARY OF THE INVENTION 
   Exhaust gas recirculation systems of this invention are used with internal combustion engines that have a number of piston cylinders with pistons slidably disposed within each cylinder. One or more piston cylinder comprises an exhaust gas port that is disposed through a wall portion of the cylinder, and that is positioned within the cylinder at a location near a bottom portion of the cylinder. Positioned in this manner, the port is exposed when the piston within the cylinder is at the bottom of its stroke (e.g., at bottom dead center). The port is covered when the piston moves upwardly within the cylinder towards the top of its stroke. 
   The system includes means for accommodating a volume of exhaust gas that is routed from the piston cylinder exhaust gas port when the piston within the cylinder is at the bottom of a work stroke. The means for accommodating is external from the engine. The exhaust gas captured by the means is reintroduced back through the exhaust gas port and into the cylinder when the piston is at the bottom of its compression stroke. Configured in this manner, the reintroduced exhaust gas operates to both improve engine combustion efficiency and engine performance. 
   The system can be configured to collect exhaust gas and reintroduce the same into the same piston cylinder, or to pass exhaust gas from one piston cylinder to a different piston cylinder, e.g., for piston cylinders having piston cycles where one piston is at a bottom of its work stroke with the other piston is at the bottom of its compression stroke. 
   EGR systems of this invention can be used with turbocharger engines, where suitable connection means is provided to direct exhaust gas from a piston cylinder exhaust gas port to an exhaust inlet of a turbocharger turbine housing. 
   Pulsed turbocharger systems of this invention are designed to operate on a pulsed, i.e., non-continuous, exhaust gas flow that is provided from an engine cylinder during a piston work stroke. The system comprises an internal combustion engine comprising a piston cylinder and a piston slidably disposed within the cylinder. 
   The engine cylinder includes an exhaust gas port that is disposed through a wall section of the cylinder. The exhaust gas port is positioned near a bottom portion of the cylinder such that: (1) an opening of the port is exposed when the piston is at the bottom of its stroke within the cylinder; and (2) an opening of the port is covered when the piston is moved towards the top of its stroke. 
   The system includes a turbocharger that is connected to the engine. The turbocharger comprises a turbine wheel that is in exhaust gas flow communication with the exhaust gas port. The system is designed so that pulsed exhaust gas exits the piston cylinder through the exhaust port, when the piston is near a bottom portion of its work stroke. This pulsed exhaust gas is directed to the turbine wheel to cause the turbocharger to produce boost air for directing to the engine. 

   
     DESCRIPTION OF THE DRAWINGS 
     The details and features of the present invention will be more clearly understood with respect to the detailed description and drawings in which: 
       FIGS. 1A  to  1 D are schematic views of a first embodiment EGR system of this invention at different points of operation; 
       FIG. 2  is a schematic view of a second embodiment EGR system of this invention; and 
       FIG. 3  is a schematic illustration of a pulse only turbocharger system constructed according to principals of this invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   EGR systems of this invention are adapted to remove exhaust gas directly from an independent exhaust port within an engine piston cylinder for either subsequent storage in an EGR tank for later reintroduction into the piston cylinder at a later time, i.e., during the piston intake stroke, or for direct introduction into a different piston cylinder, i.e., a piston cylinder that is  360  degrees out of phase so that a piston within the cylinder is entering its intake stroke. 
   A first EGR system embodiment, prepared according to principles of this invention, is schematically illustrated in  FIGS. 1A  to  1 D at different points or phases of operation. The first embodiment system  10  comprises an internal combustion engine piston cylinder  12  having at least one intake valve  14  and at least one exhaust valve  16  positioned adjacent a top portion of the cylinder, e.g., within a cylinder head. A piston  18  is positioned within the cylinder  12  and is attached to an engine crankshaft (not shown) to provide reciprocating axial up and down movement within the cylinder  12  in response to crankshaft rotation, as common with all conventional gasoline and diesel-powered internal combustion engines. 
   An exhaust gas port  20  is positioned near a bottom portion of the cylinder  12  and extends through a portion of the cylinder sidewall. The exhaust gas port  20  is independent of the exhaust valve  16  and exhaust manifold that is related thereto (not shown). The exhaust port  20  is positioned near a bottom portion of the piston cylinder  12  so that when the piston  18  is at a bottom dead center (BDC) position of its stroke at least a portion of the exhaust port opening is exposed to the open cylinder, i.e., the top surface of the piston resides at least a portion of the way below a portion of the exhaust port opening. Positioned in this manner, the exhaust port  20  is designed to receive a portion or by-pass stream of the combustion exhaust gas within the cylinder when the piston cycles through its BDC stroke position. 
   A conduit or duct  22  formed from suitable tubing, manifolding, and the like is connected to the exhaust port  20  to facilitate routing the by-pass exhaust gas from the cylinder  12  to an EGR tank  24 . The EGR tank  24  can be attached to the engine or engine compartment and is adapted to retain a desired volume of the by-pass exhaust gas at a desired pressure. The EGR tank  24  can include a cooling means to cool the received by-pass exhaust gas a predetermined amount before being reintroduced back into the piston cylinder for combustion. In an exemplary embodiment, the EGR system comprises an independent EGR tank  24  for each piston cylinder. Accordingly, an EGR system of this invention adapted for use with an eight-cylinder engine comprises eight EGR tanks, each attached to an exhaust port of a respective piston cylinder. 
   The EGR tank  24  can include a valve  26  attached thereto that is used to adjust the amount of by-pass exhaust gas contained therein. The valve is actuated, opened or closed, by suitable control means to regulate the amount of by-pass exhaust gas that is reintroduced into the cylinder  12  according to engine operating conditions. Alternatively, rather than or in addition to using a valve on the EGR tank, the exhaust valve  16  timing of the engine can be adjusted to regulate the amount of by-pass exhaust that passes through the exhaust port, e.g., the exhaust valve timing can be adjusted so that the exhaust valve opens before the exhaust port is shut off by the piston to reduce exhaust gas pressure in the cylinder and related by-pass exhaust gas flow into the EGR tank. 
   The first embodiment EGR system  10  works as follows with reference to  FIGS. 1A  to  1 D.  FIG. 1A  illustrates the EGR system  10  when the piston  18  is at BDC of its power stroke, when the piston cylinder  12  is full of combustion exhaust gas. When the piston  18  is moving downwardly in its labor stroke within the cylinder approaching BDC both valves  14  and  16  are closed, and the piston top surface begins to pass below and expose the exhaust port  20 , thereby causing a portion of the exhaust gas within the cylinder  12  to pass through the exhaust port  20  and into the conduit  22 . Configured in this manner, the downwardly moving piston acts to open the exhaust port. The exhaust gas flows under high pressure and velocity through the exhaust port  20  and conduit  22 , and into the EGR tank  24 . 
     FIG. 1B  illustrates the EGR system  10  at a point when the piston  18  is at the top of its exhaust stroke within the cylinder  12 , acting to push the remaining exhaust gas out of the cylinder through the opened exhaust valve  16 . When the piston  18  moves upwardly from its BDC position in  FIG. 1A , the top surface of the piston closes off the opening to the exhaust port  20 , both terminating exhaust gas flow into the EGR tank and preventing the EGR exhaust gas from reentering the cylinder. During this point of operation, the exhaust gas trapped in the ERG tank can be cooled by suitable cooling means before being reintroduced into the cylinder. Such exhaust gas cooling is desired to increase the density of the combustion air-fuel mixture within the cylinder combustion chamber, which is known to increase combustion energy. 
     FIG. 1C  illustrates the EGR system  10  at a point when the piston  18  is at the bottom of its intake stroke within the cylinder  12 , acting to receive an air-fuel mixture therein via the intake valve  14 . When the piston  18  moves downwardly from its position at the top of the cylinder in  FIG. 1B , the top surface of the piston passes below the opening of the exhaust port  20  allowing exhaust gas contained within the conduit  22  and EGR tank  24  to be passed therefrom and be reintroduced into the cylinder  12 . 
   At this stage of the piston operation, the in-cylinder pressure of the air-fuel mixture is less than that of the exhaust gas trapped within the EGR system so that the exhaust gas is rapidly reintroduced back into the cylinder once the exhaust port is exposed by the piston. In fact, the exhaust gas flow into the cylinder at this point is so powerful that estimated EGR amounts are expected to exceed  10  to  15  percent of the total gas mass in the cylinder at the moment that the compression stroke is started, i.e., at the moment that the piston begins to move upwardly within the cylinder after receiving the exhaust gas. During this point of operation, with the piston at the bottom of its travel within the cylinder, the exhaust and intake valves are preferably closed so that the reintroduced exhaust gas contributes to and mixes with the air-fuel mixture contained in the cylinder for subsequent combustion. 
     FIG. 1D  illustrates the EGR system  10  at a point when the piston  18  is at top dead center (TDC) of its combustion stroke within the cylinder  12 . As the piston  18  is moved upwardly within the cylinder  12  from its position at the bottom of the cylinder in  FIG. 1C , the piston top surface moves upwardly and passes over to close the opening of the exhaust port  20 , thereby terminating further reintroduction of exhaust gas into the cylinder. During this point of operation both the exhaust valve and intake valve are closed for combustion of the air-fuel and exhaust gas mixture contained within the cylinder. 
     FIG. 2  illustrates a second embodiment EGR system  30  prepared according to principles of this invention. The second embodiment EGR system  30  includes an exhaust port  32  positioned within each piston cylinder  34  as discussed above and illustrated in  FIGS. 1A  to  1 D. The exhaust port  32  in each piston cylinder  34  is adapted to receive exhaust gas from and introduce exhaust gas into a piston cylinder as discussed above. However, a primary difference between the two EGR system embodiments is that, unlike the first EGR embodiment, in the second embodiment EGR system the removed exhaust gas is not stored for later reintroduction into the same cylinder, but is transported to another different cylinder for immediate introduction therein. 
   A four cylinder engine has been illustrated in  FIG. 2  for purposes of reference only and is not intended to be limiting with respect to the different types of engine applications second embodiment EGR systems of this invention can be used with. Exhaust gas conduits  36  are attached to and are in gas flow communication with respective exhaust ports  32  of each piston cylinder  34 . Rather than being connected to individual EGR tanks, each conduit  36  is either routed directly to the exhaust port of a different cylinder, or is routed to an EGR tank  38  that is common to another conduit, exhaust port, and piston cylinder. The EGR tank  38  can include means for cooling down or reducing the temperature of the incoming exhaust gas for the reasons discussed above. 
   In an exemplary embodiment, the EGR system comprises at least two EGR tanks  38  that are each connected to more than one piston cylinder. The piston cylinders that are connected to a common EGR tank  38  are those that contain pistons having operating cycles that are opposed from one another by 360 degrees, e.g., that contain a piston in one cylinder that is at BDC (as illustrated in  FIG. 1A ) of its work stroke while a piston in another cylinder is at BDC of its compression stroke (as illustrated in FIG.  1 C). 
   Looking at the four cylinder engine embodiment of  FIG. 2 , and numbering the engine cylinders  1  to  4  (moving from left to right across the figure), the pistons  40  in cylinder numbers  1  and  4  are configured on the engine crankshaft to move at the above-described opposed 360 degree stroke cycle with respect to one another. Similarly, the pistons  40  in cylinder numbers  2  and  3  are also configured on the engine crankshaft to move at the above-described opposed 360 degree stroke cycle with respect to one another. Exhaust gas conduits  36  leading from the exhaust ports  32  of cylinder numbers  1  and  4  are connected to a first common EGR tank  38 , and exhaust gas conduits  36  leading from the exhaust ports  32  of cylinder numbers  2  and  3  are connected to a second common EGR tank  38 . 
   Configured in this manner, exhaust gas exiting cylinder number  1  at its BDC position (as illustrated in  FIG. 1A ) passes through the exhaust port  32 , into the respective conduit  36 , and into the first common EGR tank  38 . The exhaust gas entering the first common tank  38  is then passed, after cooling if desired, therethrough, through the gas conduit  36  and exhaust port  32  of cylinder number  4 , where the exhaust gas enters the cylinder and is mixed together with the air-fuel mixture before combustion. The flow of exhaust gas reverses from cylinder number  4  to cylinder number  1  after the air-fuel exhaust gas mixture in cylinder number  1  is combusted. The same cycle of EGR exhaust gas passage between cylinders occurs with cylinders  2  and  3 . 
   EGR system embodiments of this invention are intended to be used with internal combustion engines that are normally aspirated, supercharged, and turbocharged. Use of these EGR systems with turbocharged internal combustion engines is especially desirable to provide increased compression pressure within the piston cylinder at low turbocharger boost conditions, e.g., during low engine rpms. Accordingly, EGR systems of this invention are intended to be used in conjunction with turbochargers to both improve the low rpm performance of the engine, and improve NO x  reduction. 
     FIG. 2  illustrates an EGR system  30  of this invention as used with a turbocharger  48 . In such application, the EGR system is configured to route exhaust gas directly to an exhaust inlet  50  of a turbocharger turbine housing  52  comprising a turbine wheel (not shown) rotatably disposed therein. Exhaust gas conduits  42  extend from and are in gas flow communication with conduits  36  leading from cylinder numbers  3  and  4 , i.e., cylinders that include pistons that do not operate at an opposed 360 degree stroke cycle. 
   Valves  44  are positioned at the connection point of each conduit  44  to regulate the amount of exhaust gas that is passed through the conduits and into a manifold  46  that is connected to a turbine  48 . The manifold  46  is connected to the turbine housing exhaust inlet  50  so that exhaust gas passing therein it directed to the turbine wheel. The turbine wheel is connected by a common shaft to a compressor impeller (not shown) that is rotatably disposed within a compressor housing of the turbocharger. Thus, the exhaust gas directed to the turbine wheel from the EGR system operates to rotate the turbine wheel and drive the compressor impeller to provide pressurized intake air for routing to the engine induction system. The back pressure associated with operating such a turbocharger in conjunction with the EGR system is not believed to impact engine performance as it only sees this pressure near the bottom of the piston stroke which causes very little mechanical load in the rotational movement of the crankshaft. 
   Pulse only turbocharger systems of this invention are adapted to receive a pulsed stream of exhaust gas taken directly from one or more engine piston cylinders during a piston work stroke in each such cylinder. The pulsed exhaust gas stream is used to drive a turbine of a turbocharger, which actuates a compressor to provide boosted or pressurized intake air into one or more engine cylinders. 
     FIG. 3  illustrates a schematic view of a pulse only turbocharger system  60  of this invention. The system  60  comprises an internal combustion engine comprising a number of piston cylinders  62  each having at least one intake valve  64  and at least one exhaust valve  66  positioned adjacent a top portion of the cylinder, e.g., within a cylinder head. A piston  68  is positioned within the cylinder  62  and is attached to an engine crankshaft  70  to provide reciprocating axial up and down movement within the cylinder  62  in response to crankshaft rotation, as common with all conventional gasoline and diesel-powered internal combustion engines. 
   An exhaust gas port  72  is positioned near a bottom portion of the cylinder  62  and extends therethrough. The exhaust gas port  72  is independent of the exhaust valve  66  and is positioned near a bottom portion of the piston cylinder  62  so that when the piston is at the bottom dead center (BDC) of its work stroke at least a portion of the exhaust port  72  is exposed to the open cylinder, i.e., at BDC the top surface of the piston resides at least a portion of the way below an opening of the exhaust port. Positioned in this manner, the exhaust port  72  is designed to receive a portion or by-pass stream of the combustion exhaust gas within the cylinder when the piston cycles through the BDC portion of its work stroke. 
   A conduit or duct  74  formed from suitable tubing, manifolding and the like is attached to the exhaust port  72  to facilitate routing the by-pass exhaust gas from the cylinder  62  to a turbocharger  76  and, more specifically to an exhaust inlet of a turbocharger turbine housing  78 . The turbocharger is attached by conventional means to the engine or engine compartment. Pulse only turbocharger systems of this invention can be configured having many turbochargers that are each matched to a respective piston cylinder, i.e., to each receive a pulsed exhaust gas stream from a single piston cylinder, or can be configured having one or more turbochargers that are matched to more than one piston cylinder, depending on the particular internal combustion engine design and application. An exemplary pulse only turbocharger system comprises a number of suitably sized turbochargers that equal the number of engine cylinders that are each in exhaust gas flow communication with a respective piston cylinder. 
   The turbine housing  78  includes a turbine exhaust outlet  30  that is connected to an exhaust outlet pipe  82 . The exhaust outlet pipe  82  is connected to an exhaust manifold pipe  84  that receives exhaust gas from the cylinder  62  via the exhaust valve  66  during the normal operation of the engine. A catalytic converter  86  can be positioned within the engine exhaust system downstream of the turbocharger exhaust outlet pipe  82  to address engine exhaust emission requirements. The engine exhaust system can also include a small pre-catalytic converter  88  positioned within the exhaust manifold pipe  84  upstream of the turbocharger exhaust outlet pipe  82 . It has been determined that catalyst light up can be dramatically improved, when compared to conventional turbocharger exhaust attachments, by placing a valve  90  within the conduit  74  to by-pass the turbocharger  76 , thus causing all of the exhaust gas and related heat to pass from the cylinder via the exhaust valve  66  and through both catalysts  86  and  88 .  25  The valve  90  can be operated by an engine control system and the like to close off the turbocharger exhaust gas inlet, e.g., when the vehicle is first started for a period of time until the catalytic converters are lit off and the desired engine exhaust emissions are achieved. Once the desired engine exhaust emissions are achieved, the valve  90  is opened to permit the flow of pulsed exhaust gas to the turbocharger  76 . The size and specifications of the pre-catalytic converter  88  should be chosen so that the exhaust output characteristics are not significantly changed when the valve  90  can be opened and the amount of exhaust flow through the pre-catalytic converter  88  is reduced. 
   As true with conventional turbochargers, a turbocharger turbine disposed within the turbine housing  78  is connected to a turbocharger compressor disposed within a compressor housing  92  via a common shaft  94 . Inlet air enters the compressor via an air inlet  96 , is pressurized a desired amount, and exits the compressor via an air outlet  98 . The amount by which the air within the air outlet  98  is pressurized or boosted depends on the operating conditions of the engine. The pressurized air leaving the turbocharger is routed through the air outlet  98  into a cooler  100 , e.g., an intercooler, where the temperature of the air is reduced before being introduced into the piston cylinder  62  via the intake valve  64  for combustion with an air-fuel mixture. 
   The above-described pulse only turbocharger system of this invention is driven by pulse only exhaust gas pressure and heat to provide a positive pressure difference across the cylinder as follows. As the piston  68  travels downwardly during its work stroke (after combustion) the piston top surface passes below an opening of the exhaust port  72 , allowing a portion of the combustion exhaust gas to enter the conduit  74  and drive the turbocharger turbine. As the piston  68  moves upwardly during its exhaust stroke, after hitting its BDC position, the piston top surface moves to cover the exhaust port opening  72 , thus preventing further exhaust gas flow to the turbocharger. As the piston continues its upward exhaust stroke movement, the exhaust valve  66  opens and the exhaust gas remaining within the cylinder is evacuated therefrom and is passed through the engine manifold pipe  84 . As the piston moves upwardly in this fashion, the turbocharger compressor  92  operates to pressurize inlet air for passing to the piston cylinder via the compressor air outlet  98  and cooler  100 . 
   As the piston begins its downward intake stroke within the cylinder, the intake valve  64  opens and the boosted air and, in gasoline engines, fuel for a combustible air-fuel mixture, is introduced into the cylinder. As the piston reaches the bottom of its intake stroke the opening of the exhaust port  72  is again exposed. However, during this intake stroke there does not exist the same pressure differential that existed during the work stroke and there is no appreciable flow of the combustion mixture into the exhaust port  72 . As the piston  68  returns upward during its compression stroke, toward its top dead center (TDC) position, the intake valve  64  is closed, fuel is injected in direct injection or diesel engines, and the combustion mixture is ignited, propelling the piston downward within the cylinder into its work stroke. Each time the piston reaches its BDC position during the work stroke a portion of the combustion exhaust gas is vented through the exhaust port to the turbocharger. 
   The turbocharger system of this invention is referred to as being “pulsed” or operating under “pulsed pressure” because, unlike conventional turbocharger systems that are driven by a substantially uninterrupted flow of exhaust gas, turbocharger systems of this invention are driven by a pulse of exhaust gas provided only when the piston passes through the BDC of its work stroke. 
   Advantages of pulse only turbocharger systems of this invention when compared to convention turbocharger systems, i.e., those driven by an uninterrupted exhaust gas stream, is that: (1) it places a minimal load/stress on the engine because any backpressure associated with the turbocharger is provided at the base of the cylinder and along the base or side of the piston, thereby minimizing the load pressures transmitted to the engine crankshaft; and (2) it does not impose a high exhaust backpressure on the engine, which can rob the engine of pumping energy. 
   Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention. 
   Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention.