Abstract:
An exhaust gas recirculation system for an internal combustion engine includes an exhaust manifold and at least one exhaust flow control valve located between the engine and the exhaust manifold. The exhaust flow control valve diverts a portion of the exhaust gas from each cycle of one cylinder and feeds that diverted portion to another of the cylinders through an exhaust gas recirculation passage, bypassing the exhaust manifold, whereby an exhaust stroke of a piston within the one cylinder serves to pump exhaust gas through the exhaust flow control valve in another cylinder.

Description:
FIELD OF THE INVENTION 
     This invention pertains to a controllable, high pressure exhaust gas recirculation (EGR) system for engines and reduction of emissions. 
     THE PRIOR ART 
     EGR is conventionally used as a method to control (reduce) the emissions of oxides of nitrogen (primarily NO 2  and NO) from engines. In a conventional EGR, a portion of the exhaust gas from the engine is returned to the engine to become a portion of later cylinder charge. Because the oxygen content of the cylinder charge is reduced and the temperature of the gases during and after combustion is reduced, oxides of nitrogen are reduced. 
     In reciprocating internal combustion engines, during the exhaust gas stroke not all of the exhaust gas leaves the cylinder. This gas that remains (the residual gas) is mixed with the fresh air charge during the intake process. EGR systems increase and provide control of higher than baseline residual gas concentrations in the cylinder. EGR systems may also control EGR flow temperatures and EGR flow within the cylinder. 
     EGR systems may be categorized in accordance with the flow path of the exhaust gases therein and in accordance with the nature of the processes the recirculated exhaust gas undergoes in the flow path. 
     Internal EGR Systems: In this class of EGR systems, the parameters that influence the concentration of residuals in the cylinder are utilized to change the amount of residual gas. Important parameters are exhaust valve timing, intake valve timing, and exhaust backpressure. To the extent that one or more of these parameters is variable and controllable, the resultant system can control EGR. In this class of systems, in essence, the cylinder provides its own EGR. 
     External EGR Systems: In this class of EGR systems, exhaust gas is routed into the cylinder, and the exhaust gas introduced into a given cylinder is provided from more than just that one cylinder. 
     All prior art methods and devices used to perform the function of exhaust gas recirculation involve picking up part of the exhaust gas flow downstream of the exhaust valve and transferring it to an introduction point in the intake system of the engine. 
     A conventional EGR system is depicted in FIG.  1 . FIG. 1 is a schematic of the air and exhaust flows through an engine and the routes for exhaust gas recirculation. While FIG. 1 is a schematic of a turbocharged engine for the purposes of illustration, such conventional EGR systems can be used with non-turbocharged engines (naturally aspirated engines), as well as with supercharged engines. In a non-turbocharged engine, the units C and perhaps D and J can be eliminated, and in the supercharged unit, J would be eliminated. 
     The inlet air and exhaust gas components of the conventional system illustrated in FIG. 1 are labeled A through M, respectively and the junctions between adjacent components are labeled  1  through  12 , respectively. 
     Exhaust gas may be picked up at one of points  9 ,  10 ,  11 , and  12 , and introduced into the engine at one of points  1 ,  2 ,  3 ,  4 , and  5 . In the external loop, the EGR treatment apparatus N is one that is used to control recirculated exhaust gas temperature, to filter or catalyze the exhaust gas, or for other purposes. The EGR pump apparatus O can be any of the commonly know pumps whose purpose is to increase the pressure of the recirculated exhaust gas to allow the recirculated exhaust gas to be introduced at the desired location. The exhaust gas after-treatment apparatus K treats the exhaust gas to remove gaseous and/or particulate pollutants. The heat exchanger D in the intake charge stream is typical of current practice with boosted engines and is used to lower or otherwise control the temperature of the inlet charge. 
     The flow of EGR is controlled by means of a valve called an EGR valve which can be placed in any of the dotted lines in FIG.  1 . The purpose of the EGR valve is to control the flow of EGR into the engine since too little EGR may not give the emission reduction desired and too much EGR can cause combustion problems which can lead to increased smoke, particulates, and unburned fuel emissions. 
     External systems have a subclass system in which the EGR is admitted through the intakes valve(s). These External Intake-valve-admitted (EI) systems represent current practice for many engines. The two basic types of EI systems are those in which the pressure is characterized as High (EIH) or Low (EIL). An example of an EIH system would be one in which the EGR pickup is in the high pressure area—upstream of the turbocharger turbine (at  9  in FIG.  1 ), and the EGR admission is downstream of the turbocharger compressor (at  3  in FIG.  1 ). This high pressure circuit is an example of an EIH system. An example of an EIL system is one in which the EGR pickup is downstream of the exhaust after-treatment device (at  11  in FIG.  1 ), and the EGR inlet is downstream of the air cleaner (at  2  in FIG.  1 ). 
     The challenges that EGR systems must meet are good cylinder-to-cylinder distribution and fast transient response. If the same amount of exhaust gas relative to fresh charge is not provided to each cylinder, less than optimum performance will result. If the system cannot respond quickly enough to changes in power required of the engine, then the transient response of the engine will be poorer. 
     A substantial problem with current practice is the ability of an EGR system to respond quickly to changes. Consider the case of a fuel injection engine in which the fuel charge is controlled electronically. With modern fuel injection systems, the change in fuel injected can be quite rapid, changing from a very low quantity, for example, the ideal fuel injection amount, to the full load injection amount on the next injection event. For a Diesel engine, the fact that fuel changes can be made from cycle to cycle has potential for fast response to load demands, if the changes in the air and EGR charge into the engine can be made as quickly. Unfortunately, for current practice the response of the air/EGR charge is much slower than that of the fuel. In the example given, the transition from low fuel quantity to high fuel quantity will result in unacceptable emissions of smoke and particulate matter because for most systems, as the fuel quantity injected increases beyond a given level, the EGR amount is reduced to provide adequate oxygen in the charge to result in good combustion. In the example given, when the fuel is increased dramatically there is too much exhaust gas in the inlet system and even if the EGR valve is switched to the OFF (no flow) position, it takes some time for the volume between the EGR valve and the inlet valves to attain the proper value of EGR (much lower or even zero) for the example case. 
     Therefore, current systems have their transient response limited by the response of the air/EGR system which is much slower than it could be, leading to poorer transient response and vehicle driveability. The response is slow because the volume of the EGR system from exhaust valve to intake is too large compared to the displacement of the engine. 
     For current practice EGR systems, the EGR flow is a function of (1) the pressure difference between the EGR pickup point and the EGR admission point and (2) the EGR valve opening. For current high pressure systems for use with turbocharged engines, the relationship pressure difference is such that EGR is possible only over a narrow engine load range from zero to about 30 percent, since above that range the EGR admission point pressure exceeds the pressure at the EGR pickup, and EGR flow is not possible. This problem is discussed in SAE paper 970542. 
     The conventional EGR systems are not fast enough to provide the desired control during transients and, accordingly, a faster responding system is needed. In addition, the prior art systems are incapable of recirculating exhaust gas during some engine conditions due to an adverse pressure gradient, leading to the need for a higher pressure system. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an exhaust gas recirculation (EGR) system which responds more quickly to changes in engine operation, i.e. a faster transient response. 
     Another object of the present invention is to provide an EGR system capable of generating high pressures to enable EGR flow over a wide variety of engine conditions. 
     A further object of the present invention is to provide such a faster response EGR system which is applicable to engines of any aspiration type, naturally aspirated, turbocharged, or supercharged. 
     Another object of the present invention is to utilize the engine as a pump for the EGR. 
     The foregoing objectives are achieved by the present invention. Toward this end, the present invention provides a unique exhaust circulation system which controls the flow of EGR in a manner different from the prior art, with emphasis placed on control of EGR from the exhaust side of the engine. 
     The exhaust gas recirculation system of the present invention is adaptable to most, if not all, internal combustion engines having a plurality of cylinders defining respective combustion chambers, each with its own intake and exhaust valves. The exhaust recirculation system of the present invention includes at least one exhaust gas manifold for receiving exhaust gas from the plural cylinders through exhaust lines respectively connected to exhaust valves of the cylinders. An exhaust gas flow control valve is associated with each of the cylinders and is located within one of the exhaust lines. The exhaust gas flow control (EFC) valves each receive exhaust gas from the cylinder associated therewith and apportions the received exhaust gas between a first portion fed to the exhaust manifold and a second portion fed to another cylinder through an exhaust gas recirculation passage. 
     The present invention may use an exhaust manifold, portions of which are smaller in flow diameter than the conventional exhaust manifolds. 
     The present invention adds passages, valving, and controls to the conventional exhaust system to allow the exhaust to be pumped from one cylinder into another using the engine&#39;s own cylinders as exhaust gas pumps, thus providing a high pressure, fast acting EGR system. 
     Control of the flow from the pumping cylinder to the receiving cylinder is obtained via the action of the Exhaust Flow Control (EFC) valve. This valve controls the exit of exhaust gases to the exhaust manifold. When the EFC valve blocks the path of the exhaust gases to the exhaust manifold, exhaust gas cannot enter the exhaust manifold and, therefore, is pumped from the pumping cylinder into the receiving cylinder. When the EFC valve does not block the path of the exhaust gas to the exhaust manifold, exhaust gas can pass through to the exhaust manifold. There can be one EFC valve for each cylinder or one for more than one cylinder. 
     For example, in a 4-cylinder engine there are two intake events and two exhaust events for each crankshaft revolution. This means that if, for example, one EFC valve controls the EGR flow for all four cylinders, then the EFC valve must open and close two times during one engine revolution. In an embodiment with two EFC valves controlling the EGR flow of four cylinders, i.e., two cylinders per EFC valve, each EFC valve opens and closes once during one engine revolution. In an embodiment with four EFC valves, each EFC valve opens and closes once during two engine revolutions. 
     Any of a number of types of valves can be used for the EFC valve in the present invention, including poppet valves, rotary valves, disc valves, etc. 
     Admission of the pumped EGR is usually to the cylinder via the intake valves. The admission can also be via the exhaust valves, or via both intake and exhaust valves, but a more complicated valve event control is needed. The flow paths for the recirculated exhaust gas can be fully contained within the engine cylinder head, or some parts of the flow path can be external to the cylinder head, and the flow paths can include EGR flow treatment such as heat exchangers and/or filters. 
     Since the engine is also a pump for the EGR, the performance of the pumping piston in transferring exhaust gas to the receiving cylinder is important. For effective transfer of exhaust gas, the volume of the flow passage from the pumping piston to the receiving cylinder should be small compared to the displacement of the pumping cylinder. For the most flexible system, the volume of the pumping passage could be selected so that the pressure generated by the pumping cylinder exceeds the highest value of inlet manifold pressure for the engine. In this case, EGR can be used at any operational condition of the engine, if necessary. 
     This pumped EGR system has a rapid response to commands for changes in EGR rate. The EGR rate is controlled by the timing of the EFC valve(s), and the volume of the transfer passages is small. 
     For the fastest response to a command to reduce EGR rate, an additional flow control valve is positioned at the entrance to the intake port in the embodiment in which the pumped EGR is admitted to the intake system. These valves may be reed valves or check valves or other valves known to those skilled in the art. In this case, the volume to purge approaches zero, and the response is determined by the response of the main EFC valve(s). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a prior art exhaust gas recirculation system. 
     FIG. 2 is a schematic representation of an exhaust gas recirculation system according to a first embodiment of the present invention. 
     FIG. 3 is a schematic representation of an exhaust gas recirculation system according to a second embodiment of the present invention. 
     FIG. 4, is a schematic representation of an exhaust recirculation system according to a third embodiment of the present invention. 
     FIG. 5 is a schematic view of a preferred camshaft arrangement. 
     FIG. 6 is a schematic view of the cylinder head showing the camshafts, a phase varying device and four of the camshaft lobes. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 2 shows one preferred embodiment wherein the present invention is applied to a turbocharged, 4-cylinder, four stroke cycle engine. The embodiment has the firing order:  31 - 33 - 34 - 32 . Cylinder  33  pumps exhaust gas into cylinder  31 , cylinder  34  pumps exhaust gas into cylinder  32 , cylinder  32  pumps EGR into cylinder  34 , and cylinder  31  pumps EGR into cylinder  32 . This embodiment has one EFC valve unit for each cylinder, for a total of four (4) EFC valve units. Each EFC valve unit ( 41 ,  42 ,  43  and  44 ) incorporates two poppet valves. The EFC valves are driven from a camshaft which, in turn, is driven from the camshaft of the engine and which operates at the same speed as the engine&#39;s camshaft, one-half of the engine&#39;s crankshaft speed. Cams on the EFC camshaft operate the EFC valves. One of the poppet valves in each EFC valve unit controls flow to the EGR passage, while the other poppet valve in the EFC valve unit controls flow to the exhaust manifold  50 . The two poppet valves associated with a given cylinder have a degree of overlap, which is denoted by θ o . In the this embodiment, the valve event for the valve controlling flow to the exhaust manifold precedes the valve event for the valve controlling the EGR flow (the reverse is also possible). 
     During the engine exhaust event, the EFC valves  41 ,  42 ,  43  and  44  receive exhaust gas from cylinders  31 ,  32 ,  33  and  34  through exhaust passages  311 ,  321 ,  331  and  341 , respectively, and apportion the exhaust flow first to the exhaust manifold  50  through exhaust passages  412 ,  422 ,  432  and  442  and to the respective EGR passages  411 ,  421 ,  431  and  441 . 
     By way of example, EFC valve  41  receives exhaust gas from a single combustion chamber within cylinder  31 , more specifically, from an exhaust valve El of cylinder  31  through exhaust line  311 . EFC valve  41  apportions the received exhaust gas, in sequence, to feed a first portion to the intake port I 2  of cylinder  32 , through EGR passage  411  and through heat exchanger HX 1  and through the one-way reed valve R 2 . EPC valves  41 ,  42 ,  43  and  44  operate in similar fashion. 
     Referring to FIG. 2, the combination of exhaust passages  311  and  412 , for example, can be regarded as a single exhaust line with flow therethrough regulated by EFC valve  41 . 
     As is further shown in FIG. 2, EGR passages  411 ,  421 ,  431  and  441  are respectively provided with one-way valves, i.e. conventional reed valves R 1 , R 2 , R 3  and R 4 . Further, EGR passages  441  and  421  pass through heat exchanger HX 2  whereby the recirculated exhaust is cooled by countercurrent heat exchange with engine coolant prior to entering cylinders  33  and  34  through intake poppet valves I 3  and I 4 , respectively. 
     The amount of EGR is varied by changing the phase of the EFC valves in relation to the cylinder exhaust valve. Changing the phase of the EFC valves&#39; camshaft so that the EFC poppet valve controlling the flow into the EGR passage is open for a greater portion of the cylinder exhaust event increases the EGR rate, and changing the phase of the EFC valves&#39; camshaft so that the poppet valve controlling the flow into the EGR passage is open for a lesser portion of the cylinder exhaust event decreases the EGR rate. The mechanism for altering the phasing of the EFC valves&#39; camshaft can be a helical spline which is known to those skilled in the art and which has been used to change timing of engine valves and to change the timing of fuel injection pumps. 
     The pumped EGR flow path includes heat exchangers which can be of the counterflow type and which uses engine coolant as the heat exchange medium. Reed valves are positioned at the points where EGR flow enters the intake manifold. 
     For the subject invention, the performance of the system depends on the ratio of the volume of the EGR passage to the displacement of one cylinder (V E   p /D cyl ), the ratio of the duration of the EFC valve(s) to the exhaust valves (θ d /θ e ), the ratio of the lift of the EFC valves to the lift of the exhaust valves (L d /L e ) the overlap between the valve controlling the flow into the exhaust manifold and the valve controlling the flow into the EGR passage (θ o ), and the phasing of the EFC valve events to the exhaust timing of the engine (θ p ). 
     For the subject invention, the extreme and preferred ranges of the important parameters are shown in Table 1. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Parameter Values 
               
             
          
           
               
                 Parameter 
                 Extreme Range 
                 Preferred Range 
               
               
                   
               
               
                 VE p /D cyl   
                 0.01 to 1.00 
                 0.02 to 0.50 
               
               
                 θ d /θ e   
                 0.25 to 1.50 
                 0.50 to 1.00 
               
               
                 L d /L e   
                 0.25 to 1.50 
                 0.75 to 1.25 
               
               
                 θ o   
                     0° to θ d /2 
                 30° to 90° 
               
               
                   
               
             
          
         
       
     
     The materials required for this invention are similar to those used for exhaust systems today. Any new materials which can be used for exhaust valves, manifolds, etc. can also be used for this invention. 
     FIG. 3 shows a second embodiment of the present invention applied to an engine having multiple (two or more) exhaust valves. In FIG. 3, this second embodiment is shown as applied to an engine with two intake valves I 1  and I 2  and two exhaust valves E 1  and E 2  per each of cylinders  60 ,  62 ,  64  and  66 . In this embodiment, the exhaust valve ports are separated. One exhaust port E 1  from each cylinder leads to the exhaust manifold  70 , through one of exhaust passages  611 ,  612 ,  613 ,  614 , and the other exhaust port E 2  from each cylinder leads to one of the EGR passages  615 ,  616 ,  617  and  618 . The two exhaust valves E 1  and E 2  in each cylinder have a degree of overlap, and the exhaust valve E 1  which controls the flow to the exhaust manifold  70  leads the exhaust valve E 2  which controls flow to one of the EGR passages. In this embodiment, the amount of EGR is controlled by varying the phasing of the exhaust valve camshaft of the engine in the same way that the phasing of the EFC valves&#39; camshaft is controlled in the first preferred embodiment discussed earlier. 
     Many configurations of this embodiment are possible, depending on the base engine valve configuration. Configurations include those applicable to: (1) an engine with two conventional gas exchange valves, (2) an engine with three conventional gas exchange valves, (3) an engine with four conventional gas exchange valves, and (4) and engine with five gas exchange valves. 
     In another possible modification of the subject invention, the EGR admission point is positioned downstream of the inlet valve, so that the EGR is pumped directly into the receiving cylinder. In this case, the reed valve is replaced with a poppet valve as the EGR admission valve. In effect, the valve that controls the EGR distribution is moved to the receiving cylinder, and its operation admits EGR directly to the cylinder. 
     A third preferred embodiment (the most preferred embodiment) is shown in FIG.  4 . In this embodiment, the cylinder head configuration is such that there are four valves per cylinder. Two of these valves in each cylinder are conventional intake and exhaust valves. For the four cylinder engine configuration depicted, the conventional intakes are  81 CI,  82 CI,  83 CI, and  84 CI for cylinders  81 ,  82 ,  83  and  84 , respectively. The conventional exhaust valves are  81 CE,  82 CE,  83 CE, and  84 CE for cylinders  81 ,  82 ,  83  and  84 , respectively. 
     In FIG. 4, the cylinder head  91  contains two camshafts, the conventional camshaft  100  and the EGR camshaft  200 . On the conventional camshaft are lobes CI 1 , CE 1 , CI 2 , CE 2 , CI 3 , CE 3 , CI 4  and CE 4  control valves which are shown as  81 CI,  81 CE,  82 CI,  82 CE,  83 CI,  83 CE,  84 CI and  84 CE, respectively, in FIG.  4 . On the EGR camshaft are lobes EO 1 , EI 1 , EI 2 , EO 2 , EO 3 , EI 3 , EI 4  and EO 4  control valves which are shown as  81 EO,  81 EI,  82 EI,  82 EO,  83 EO,  83 EI,  84 EI and  84 EO, respectively, in FIG. 4. A camshaft phasing device  300  is shown attached to the EGR camshaft  200 . 
     The EGR system is positioned on one side of the cylinder head to reduce package volume and to provide for reduced transfer passage volume. The transfer passages ( 81 E 82 ,  82 E 84 ,  83 E 81 , and  84 E 83  are all enclosed in a heat exchanger (not shown in FIG. 4) to provide for temperature control of the recirculated pumped exhaust gas. The heat exchanger can be integral with the cylinder head or a separate unit or units. 
     As shown in FIG. 5, the valves for the engine depicted in FIG. 4 are operated by two separate camshafts. The conventional intake and exhaust valves are operated by one camshaft  100  (the conventional camshaft) and the EGR valves are operated by another camshaft  200 . Control of the relative phasing of the EGR camshaft and the conventional camshaft can be obtained via use of a helical spline  300  or other devices known to those skilled in the art, which are used to vary camshaft timing in engines and other machines. 
     Consider an exhaust event. For the geometry shown in FIG. 4, consider the situation where cylinder  83  is on its exhaust stroke. (The other cylinders will behave in a similar manner.) Cylinder  83  can pump its exhaust to the exhaust manifold  90  via conventional exhaust valve  83 CE and passage  831 , or it can pump its exhaust into cylinder  81  via passage  83 E 81 , reed valve R 81 , and EGR inlet valve  81 EI. 
     If conventional exhaust valve  83 CE is closed, and EGR outlet valve  83 E 0  is open, the piston in cylinder  83  will pump the exhaust gas through passage  83 E 81  and when the pressure exceeds the opening pressure of reed valve R 81 , into cylinder  81  past EGR inlet valve  81 E 1 , if it is open. This provides for EGR flow. 
     When conventional exhaust valve  83 CE opens, the pressure in the cylinder and in the passage  83 E 81  drops, reed valve R 81  closes, and the piston pumps the exhaust gas out of the cylinder through the passage  831  into the exhaust manifold  90 . 
     It can be seen that controlling the relative phasing between the valve event for valve  83 E 0  and valve  83 CE will control the amount of EGR, and when valve  83 CE opens, the EGR is effectively stopped. 
     The EGR flow can be scheduled prior to or after the conventional exhaust flow depending on the desired result. 
     The valve timing for both the conventional camshaft  100  and the EGR camshaft could be variable, or one or the other could vary relative to the other. A preferred embodiment is one in which the conventional camshaft  100  has fixed timing, and the EGR camshaft phasing is varied to control the EGR rate, via a helical spline or other method known to those skilled in the art. 
     FIG. 6 shows an end view of the cylinder head  91 . In this view the conventional camshaft lobes CI 1  and CE 1  on camshaft  100  can be seen as well as the valve  81 CI which is operated by camshaft lobe CI 1 . On the exhaust camshaft  200  side lobes EO 1  and EI 1  can be seen as well as valve  81 EO which is controlled by lobe EO 1 . The camshaft phasing device  300  is shown attached to exhaust camshaft  200 . 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.