Patent Publication Number: US-6220233-B1

Title: Exhaust gas recirculation system having variable valve timing and method of using same in an internal combustion engine

Description:
TECHNICAL FIELD 
     The present invention relates to internal combustion engines, and, more particularly, to exhaust gas recirculation systems in such engines. 
     BACKGROUND ART 
     An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine. 
     When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is preferably removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted directly from the exhaust manifold. Likewise, the recirculated exhaust gas is preferably introduced to the intake air stream downstream of the compressor and air-to-air after cooler (ATAAC). Introducing the exhaust gas downstream of the compressor and ATAAC is preferred due to the reliability and maintainability concerns that arise if the exhaust gas passes through the compressor is and ATAAC. An example of such an EGR system is disclosed in U.S. Pat. No. 5,802,846 (Bailey) issued on Sep. 8, 1998, which is assigned to the assignee of the present invention. 
     With conventional EGR systems as described above, the exhaust gas may be drawn from only a subset of the combustion cylinders within the engine, and driven back into the intake manifold. For example, the exhaust gas may be drawn from only a single cylinder of a multi-cylinder engine. In the case of a six cylinder engine, such a single cylinder EGR system would provide one-sixth of the available exhaust gases to the intake manifold, thereby providing an EGR rate of approximately 17 percent. Such an EGR rate, however, is too high under certain operating conditions, such as when the engine is operating under a peak torque condition. 
     Also, it is known to control the operation of the EGR valve of such conventional EGR systems by using a negative pressure source, such as an intake manifold, to sense low load conditions. However, operation of the EGR valve based on pressure changes can be adversely affected by leaks in the negative pressure source, and leaks or blockages in the control line coupling the EGR valve to the negative pressure source. 
     The present invention is directed to overcoming one or more of the problems as set forth above. 
     DISCLOSURE OF THE INVENTION 
     In one aspect of the invention, an internal combustion engine comprises a block defining a plurality of combustion cylinders, each combustion cylinder of the plurality of combustion cylinders having a displacement volume. An intake manifold provides combustion air to each combustion cylinder. An exhaust manifold includes cylinder ports fluidly connected to each combustion cylinder for selectively transporting exhaust gas therefrom through at least one of a primary exhaust outlet and a secondary exhaust outlet. An exhaust gas recirculation valve is fluidly connected between the intake manifold and the secondary exhaust outlet, and wherein the exhaust gas recirculation valve is controllably positioned in one of a first position and a second position. When the exhaust gas recirculation valve is in the first position the exhaust gas from each combustion cylinder is transported through the primary exhaust outlet, and when the exhaust gas recirculation valve is in the second position an exhaust gas flow from at least one of the plurality of combustion cylinders is transported through the secondary exhaust outlet. An actuator communicates with the exhaust gas recirculation valve for effecting a position change of the exhaust gas recirculation valve. A controller is coupled to the actuator to control a timing of movement of the exhaust gas recirculation valve between the first position and the second position based on at least one cyclical engine operation characteristic. 
     Another aspect of the invention is an exhaust gas recirculation system for an internal combustion engine. The internal combustion engine has a crankshaft, a block defining a plurality of combustion cylinders, a cylinder head having an exhaust valve, an intake manifold for providing combustion air to each cylinder of the plurality of combustion cylinders, and an exhaust manifold having cylinder ports fluidly connected to each cylinder for selectively transporting exhaust gas therefrom through at least one of a primary exhaust outlet and a secondary exhaust outlet. 
     The exhaust gas recirculation system comprises an exhaust gas recirculation valve adapted for coupling to the intake manifold and adapted for connection to the secondary exhaust outlet, the exhaust gas recirculation valve being controllably positioned in one of a first position and a second position, wherein when the exhaust gas recirculation valve is in the first position the exhaust gas from each cylinder is transported through the primary exhaust outlet, and when the exhaust recirculation valve is in the second position an exhaust gas flow from at least one of the plurality of combustion cylinders is transported through the secondary exhaust outlet. Also, the exhaust gas recirculation system comprises an actuator in communication with the exhaust gas recirculation valve for effecting a position change of the exhaust gas recirculation valve and a controller coupled to the actuator to control a timing of movement of the exhaust gas recirculation valve between the first position and the second position based on at least one cyclical engine operation characteristic of the internal combustion engine. 
     In still another aspect of the invention, a is method of recirculating exhaust gas in an internal combustion engine comprises the steps of providing a plurality of combustion cylinders having a displacement volume; providing an intake manifold for providing combustion air to each combustion cylinder; providing an exhaust manifold having cylinder ports fluidly connected to each combustion cylinder for selectively transporting exhaust gas therefrom through at least one of a primary exhaust outlet and a secondary exhaust outlet; providing an exhaust gas recirculation valve fluidly connected between the intake manifold and the secondary exhaust outlet; and controlling a timing of movement of the exhaust gas recirculation valve between a first position and a second position based on at least one cyclical engine operation characteristic, wherein when the exhaust gas recirculation valve is in the first position the exhaust gas from each combustion cylinder is transported through the primary exhaust outlet, and when the exhaust gas recirculation valve is in the second position an exhaust gas flow from at least one of the plurality of combustion cylinders is transported through the secondary exhaust outlet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of an embodiment of an internal combustion engine of the present invention; 
     FIG. 2 is a side, sectional view of the exhaust manifold shown in FIG. 1, with the remainder of the components shown in schematic; and 
     FIGS. 3A-3D graphically illustrate the operation of a exhaust gas recirculation valve in relation to cyclical operational characteristics of the internal combustion engine as shown in FIG.  1 . 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring now to the drawings, and more particularly to FIG. 1, there is shown a schematic representation of an embodiment of an internal combustion engine  10  of the present invention. Internal combustion engine  10  generally includes a block  11 , a crankshaft  12 , a cylinder head  14 , exhaust manifold  16 , turbocharger  18 , ATAAC  20 , mixing vessel  22 , intake manifold  24  and an EGR control system  26 . 
     Block  11  defines a plurality of combustion cylinders  28 . The exact number of combustion cylinders  28  may be selected dependent upon a specific application, as indicated by dashed line  32 . For example, block  11  may include six, ten or twelve combustion cylinders  28 , including an end cylinder  28   a . Each combustion cylinder  28  has a displacement volume which is the volumetric change within each combustion cylinder  28  as an associated piston (not shown) moves from a bottom dead center to a top dead center position, or vice versa. The displacement volume may be selected dependent upon the specific application of internal combustion engine  10 . The sum of the displacement volumes for each of combustion cylinders  28  defines a total displacement volume for internal combustion engine  10 . 
     Cylinder head  14  is connected to block  11  in a manner known to those skilled in the art, and is shown with a section broken away to expose block  11 . As each of the pistons moves to its respective top dead center position, each piston and the cylinder head  14  define a combustion chamber therebetween. Cylinder head  14  can be constructed as a single part cylinder head or a multi-part cylinder head. In the embodiment shown, cylinder head  14  includes a plurality of exhaust valves  30 , including an end cylinder exhaust valve  30   a.    
     Exhaust manifold  16  has cylinder ports fluidly connected to cylinder head  14  to receive combustion products from combustion cylinders  28  and transports the combustion products to at least one of a primary exhaust outlet  34  and a secondary exhaust outlet  36  through which the combustion products are discharged. 
     Turbocharger  18  includes a turbine  38  and a compressor  40 . Turbine  38  is driven by the exhaust gases which flow from outlet  34  of exhaust manifold  16 . Turbine  38  is coupled with compressor  40  via shaft  42  and rotatably drives compressor  40 . Compressor  40  receives combustion air from the ambient environment (as indicated by line  44 ) and provides compressed combustion air via fluid conduit  46 . 
     ATAAC  20  receives the compressed combustion air from compressor  40  via fluid conduit  46  and cools the combustion air. In general, ATAAC  20  is a heat exchanger including one or more fluid passageways through which the compressed combustion air flows. Cooling air flows around the fluid passageways to cool the combustion air transported through the passageways. The cooled combustion air is transported from ATAAC  20  through outlet  48 . 
     Mixing vessel  22  receives the cooled and compressed combustion air from ATAAC  20  at inlet  50 . In addition, mixing vessel  22  also receives exhaust gas from exhaust manifold  16  via fluid conduit  52  at a second inlet  54 . The exhaust gas flows through fluid conduit  52  and enters into mixing vessel  22  in a parallel flow arrangement with respect to the cooled and compressed combustion air entering through first inlet  50 . The combustion air and exhaust gas mix within mixing vessel  22  and the mixture is transported through an outlet  56  to intake manifold  24 . Intake manifold  24  provides the mixture of charged combustion air and exhaust gas to the individual combustion cylinders  28 . 
     EGR system  26  includes an EGR valve assembly  58 , a valve actuator  60 , a controller  62 , a sensor  64 , and an energy source  66 . 
     Preferably, valve actuator  60  is a fluid actuator and energy source  66  is a fluid source, such as a fluid pump. The working fluid can be, for example, hydraulic oil or air. A connector  68  provides a conduit which fluidly connects valve actuator  60  to source  66 . Accordingly, energy source  66  supplies fluid under pressure via connector  68  to valve actuator  60 . The fluid under pressure is selectively supplied to a fluid piston  70  which effects the operation of EGR valve assembly  58 . 
     Valve actuator  60  is further electrically coupled to controller  62  via a conductor  72 . Controller  62  sends control signals via conductor  72  to a switching device (not shown) in valve actuator  60 , which in turn selectively permits passage of the pressurized fluid from energy source  66  to fluid piston  70 . 
     Those skilled in the art will recognize that, alternatively, valve actuator  60 , energy source  66  and connector  68  could be formed from electrical components analogous to the above-described and preferred fluid components. 
     Preferably, controller  62  includes a microprocessor and associated memory (not shown) which effect the generation of appropriate control signals based upon one or more cyclical engine operating characteristics, such as for example, crankshaft rotational position, exhaust valve lift position, etc. Assuming that internal combustion engine  10  is a four stroke engine, a complete cycle (intake, compression, power, and exhaust) occurs during two revolutions of the crankshaft (i.e., 720°). The exhaust valves, which are typically operated by a camshaft driven by the crankshaft, are each selectively opened for a duration of, for example, about 220° to 280° of crankshaft rotation during each cycle. 
     Thus, preferably, sensor  64  communicates with crankshaft  12  to sense a rotational position, or crank angle, of crankshaft  12 . Such a crankshaft rotational position sensor, which includes a driven portion and a stationary portion (not shown), is well known in the art. The driven portion moves in conjunction with the rotation of crankshaft  12 , and the stationary portion includes a pickup which detects the movement of the driven portion. Thus, sensor  64  could be accomplished, for example, by using an encoded wheel and associated reader, or a magnet and an associated Hall-effect transistor. 
     Sensor  64  generates a sense signal which is supplied via conductor  74  to controller  62  for processing. Controller  62  processes the sense signal and generates the control signal, which is supplied via conductor  72  to valve actuator  60 . Upon receiving the control signal, valve actuator communicates with EGR valve assembly  58  via piston  70  to effect the operation of EGR valve assembly  58 . More particularly, EGR valve assembly  58  is controlled to permit the intermittent passage of a flow of exhaust gas from exhaust manifold  16  through fluid conduit  52  to mixing vessel  22 . 
     As shown in FIG. 2, preferably, EGR valve assembly  58  is associated with exhaust gas from only one of cylinders  28 , and is formed integral with exhaust manifold  16 . EGR valve assembly  58  includes a poppet EGR valve  76  which is held in a normally closed, or first, position  86  by a return spring  78 . In the normally closed position  86 , a beveled surface  80  of valve  76  contacts an annular EGR valve seat  82  formed in exhaust manifold  16 , and piston  70  is retracted into valve actuator  60 . When EGR valve  76  in the closed position  86 , all exhaust gas from all cylinders  28  is supplied to primary exhaust outlet  34 . When piston  70  of valve actuator  60  is extended, EGR valve  76  is moved to an open, or second, position  88  (shown by phantom lines) and EGR valve  76  effectively blocks the exhaust path from exhaust manifold inlet  84  to primary exhaust outlet  34 , and opens an exhaust flow path from exhaust manifold inlet  84  through secondary exhaust outlet  36 . Accordingly, the selective operation of EGR valve  76  to the open position results in a flow of exhaust gas to mixing vessel  22  of a pulsed nature, as illustrated in FIGS. 3A-3C. 
     FIG. 3A, in relation to FIG. 1, graphically illustrates the exhaust valve and intake valve operation cycle for cylinder  28   a  of internal combustion engine  10  in terms of valve lift, and further in relation to crankshaft rotational position, or crank angle, of crankshaft  12 . For purposes of this discussion, cylinder  28   a  is assumed to be the sixth cylinder of a total of six cylinders  28  of internal combustion engine  10 . The associated intake valve (not shown) begins to open at a crank angle of about 320° and becomes fully closed at about 560°, resulting in a duration of about 240°. The associated exhaust valve  30   a  begins to open at a crank angle of about 100° and becomes fully closed at about 360°, resulting in a duration of about 260°. When exhaust valve  30   a  is in open position  88 , a flow of exhaust gas is directed from cylinder  28   a  into exhaust manifold  16 . Exhaust valve  30   a  is closed during the remaining 460° of the four stroke cycle. 
     FIG. 3B graphically depicts the exhaust gas flow from sixth cylinder  28   a . As shown, about 50 percent of the exhaust gas flow occurs between crank angles of about 100° to about 180°, with peak flow occurring at about 160°. 
     FIG. 3C graphically depicts exhaust manifold pressure at a location near exhaust inlet  84  of sixth cylinder  28   a . Peak exhaust pressure occurs at a crank angle of about 170°. 
     FIG. 3D graphically illustrates the operation of EGR valve  76  in relation to the crank angle of crankshaft  12 , which can be further compared to FIG. 3A to determine a relationship to the exhaust valve lift of exhaust valve  30   a . As illustrated in FIG. 3D, EGR valve  76  is operable between the closed position  86  and the open position  88  to permit a variable amount of exhaust gas from cylinder  28   a  to be diverted through secondary exhaust outlet  36  (see FIG.  2 ). Assuming a six cylinder engine, and by way of example, diverting 100 percent of the exhaust gas from cylinder  28   a  to secondary exhaust outlet  36  will result in an EGR rate of about 17 percent for internal combustion engine  10 , whereas diverting 50 percent of the exhaust gas from cylinder  28   a  to secondary exhaust outlet  36  will result in an EGR rate of about 8 percent. 
     Preferably, controller  62  includes control logic which permits a selection of an EGR rate in a range from 0 percent through 17 percent, resulting in the diversion of 0 percent through 100 percent of the exhaust gas from sixth cylinder  28   a  to intake manifold  24 . By changing the time of application of the control signal from controller  62  to valve actuator  60 , the EGR valve timing can be varied. For example, as shown in FIG. 3D, if the EGR valve is actuated at a crank angle of about 100° for a duration of about 280°, an EGR rate of 17% is achieved. If, however, an EGR rate of about 8 percent is desired, the lift start for EGR valve  76  is delayed until a crank angle of about 180° and maintained for a duration of 200°. Alternatively, the timing of the closing of EGR valve  76  can be changed, or the timing of both the opening and closing of EGR valve  76  can be varied, to provide the desired EGR rate. Thus, by collectively comparing the illustrations of FIGS. 3A-3D, it is shown that the EGR rate of internal combustion engine  10  depends upon the timing of valve opening of EGR valve  76  and/or the duration of opening of EGR valve  76  in relation to the lift position of exhaust valve  30   a , and further in relation to the crank angle of crankshaft  12 . 
     INDUSTRIAL APPLICABILITY 
     During use, a plurality of pistons (not shown) reciprocate within combustion cylinders  28  (see FIG.  1 ). Combustion occurs within combustion cylinders  28  either via compression ignition in the case of a diesel engine or via spark ignition in the case of a gasoline engine. The exhaust gases which are discharged from combustion cylinders  28  flow through exhaust manifold  16  to turbine  38  of turbocharger  18 . Turbine  38  rotatably drives compressor  40  which receives combustion air and provides compressed combustion air to ATAAC  20 . The cooled and compressed combustion air flows into mixing vessel  22 . In addition, exhaust gas is controllably injected into mixing vessel  22  in a parallel relationship with respect to the combustion air. 
     Controller  62  includes preprogrammed instructions for processing information relating to at least one cyclical engine operation characteristic, such as crankshaft rotational position information or exhaust valve lift information, for controlling an EGR rate of internal combustion engine  10 . Preferably, this information is supplied to controller  62  by sensor  64 , which is in communication with crankshaft  12 . Depending upon the desired EGR rate, the timing of the opening, closing and/or duration of EGR valve  76  is determined, and a suitable control signal is generated. The control signal is supplied to valve actuator  60 , which in turn effects a change in the position of EGR valve  76  from a closed, or first, position to an open, or second position, based upon the cyclical engine operation characteristic information. 
     When EGR valve  76  is in the closed position  86 , the exhaust gas from all cylinders is supplied to primary exhaust outlet  34 . When EGR valve  76  is in the open position  88 , EGR valve  76  effectively blocks the exhaust path from exhaust manifold inlet  84  to primary exhaust outlet  34 , and opens an exhaust flow path from exhaust manifold inlet  84  through secondary exhaust outlet  36  to intake manifold  24  via mixing vessel  22 . Thus, an exhaust gas flow through secondary exhaust outlet  36  is recirculated back through the intake manifold  24  for combustion in combustion cylinders  28 . 
     Accordingly, an exhaust gas recirculation system of the invention advantageously provides variable valve timing for an EGR valve based on at least one cyclical engine operating characteristic. 
     Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.