Abstract:
A passageway is provided between branches of a multi-branch exhaust manifold to reduce the amount of backflow (iEGR) into the cylinders at low engine speeds. The passage is located upstream of the turbocharger and can be at the part of the manifold where the branches merge for entry into the turbo. The passageway allows exhaust pressure pulse modulation so that high iEGR levels (using iEGR through delayed exhaust valve closing for example) are avoided. The passage may be controllable to modulate the effect based on engine conditions.

Description:
TECHNICAL FIELD  
       [0001]     The disclosure relates to the field of internal combustion engines and more specifically to internal exhaust gas recirculation within such engines.  
       BACKGROUND  
       [0002]     The use of internal exhaust gas recirculation (iEGR) is a known method for reducing the amount of pollutants in the exhaust gasses of internal combustion engines. iEGR can be achieved by either introducing exhaust gas into the induction manifold or by allowing exhaust gas to flow back from the exhaust manifold into the combustion chamber during the induction stroke. DE2125368 teaches the principle of an internal exhaust gas recirculation arrangement in which exhaust gas is fed back to the combustion chamber during the intake stroke. However, problems due to exhaust gas pressure pulsations within the exhaust manifold have led to unsatisfactory results in emission control strategies. The present disclosure is aimed at overcoming one or more of the problems as described.  
       SUMMARY OF THE INVENTION  
       [0003]     In a first embodiment there is provided an internal combustion engine with a plurality of cylinders, each of the cylinders having a corresponding exhaust valve and the cylinders are divided into at least a first set and a second set. It furthermore includes an exhaust manifold, the exhaust manifold further having at least a first branch in direct fluid communication with the cylinders in the first cylinder set and a second branch being in direct fluid communication with the cylinders in the second cylinder set when the corresponding exhaust valves are in an open position.  
         [0004]     There is also an internal exhaust gas recirculation arrangement, allowing at least part of the exhaust gas to flow from the exhaust manifold into the cylinders during at least part of an intake stroke of said cylinders, and a passage located in or proximal to the exhaust manifold for fluidly connecting the first branch and the second branch adapted to reduce the flow of exhaust gas from the exhaust manifold into the cylinders.  
         [0005]     In a second embodiment there is provided a turbocharger for a multi-cylinder internal combustion engine. The internal combustion engine has a plurality of cylinders, each of the cylinders having a corresponding exhaust valve, and the cylinders are divided into sets. It further includes an exhaust manifold having at least two branches, each of the branches is in direct fluid connection with the cylinders in one of the cylinder sets when the corresponding exhaust valves are in a open position. There is also an internal exhaust gas recirculation arrangement, allowing at least part of the exhaust gasses to flow back from the exhaust manifold into the cylinders during an intake stroke of the cylinders. The turbocharger has an exhaust gas inlet, at least part of the exhaust gas inlet is adapted to maintain the gas flow separation from the cylinder sets, and a passage adapted to fluidly connect at least the at least two branches to reduce the back flow of exhaust gasses from the exhaust manifold into the cylinders. The passage is located in the exhaust gas inlet of the turbo charger.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a partial schematic isometric view of an internal combustion engine according to the present disclosure.  
         [0007]      FIG. 2  is a partial schematic RHS view of the same engine as shown in  FIG. 1 .  
         [0008]      FIG. 3  is a schematic isometric view of an exhaust manifold according to the present disclosure.  
         [0009]      FIG. 4  is a representation of a passage within an exhaust manifold such as that shown in  FIG. 3 .  
         [0010]      FIG. 5  is a schematic representation of a passage similar to that shown in  FIG. 4 , but with an additional valve.  
         [0011]      FIG. 6  is a schematic cross-sectional view of a combustion chamber and the porting arrangement of an internal combustion engines such as shown in  FIGS. 1 and 2 . 
     
    
     DETAILED DESCRIPTION  
       [0012]      FIGS. 1 and 2  show an internal combustion engine  10 . The engine  10  is shown as a six cylinder in-line, turbo-charged, compression ignition engine, but this is for illustrative purposes only. The principle of the disclosure applies to engines with more or less cylinders, to engines configured differently such as V-style engines, to naturally aspirated engines and to spark ignited engines.  
         [0013]     The engine  10  has a plurality of cylinders  11 , a cylinder block  12  and a cylinder head  14 , assembled together with a sealing arrangement in between (not shown). Connected to the cylinder head is an induction arrangement  15 , in this example shown as and induction manifold  16  with an induction pipe  18  for supplying the engine with air for the combustion process. Also connected to the cylinder head, but in this example at the opposite side of the induction arrangement, is an exhaust manifold  30  and connected thereto a turbocharger  22 . For clarity purposes not all connections to and from the turbocharger are shown, but they are mostly conventional.  
         [0014]     The exhaust manifold  30  as shown in detail in  FIG. 3  is a possible variant of the one shown in  FIGS. 1 and 2 , but the principle is the same and identical indices are used where appropriate. The exhaust manifold is a multi-branch manifold, in this case two branches are present, a first branch  32  and a second branch  34 . Each branch has three ports  32   a - c,    34   a - c,  each port  32   a - c,    34   a - c  corresponding to a single cylinder of the engine  10 . Each branch is therefore connected to three cylinders thereby artificially dividing the engine in two sections of three cylinders. The three cylinders in a group are likely to be adjacent to each other, but that may be varied if deemed appropriate. The two branches may have supporting bridge pieces  39 ,  41  in between them that do not provide fluid communication between the two branches. At the downstream end of the exhaust manifold  30  there is a flange  36  to allow a connection to the turbocharger  22 . Even though the branches may share a common wall  38 , they do not allow any mixing of the gas flows except via a passage  40  which in this example is located in the common wall as shown in  FIG. 4 . Alternatively the passage may also be a connection between the two branches upstream of the common wall  38 , for example by an external pipe (not shown). Yet another alternative is where the inlet of the turbocharger is substantially a mirror image of the corresponding counterparts of the exhaust manifold, namely the flange and the common wall. The inlet section of the turbocharger therefore appears to be an extension of the exhaust manifold. In that case the passage may be located in that part of the turbocharger that appears to extend the common wall of the exhaust manifold.  
         [0015]     Systems that maintain separate gas flows as described are common where the turbocharger  22  operates via a pulse wave method. This method relies on a compact flow of gas to ensure a quick responsive behavior of the turbocharger, the quick response relying on a separation of the various gas flows from the cylinder groups until proximal to the turbine of the turbocharger.  
         [0016]     The passage  40  may be controllable by a valve  42  as shown in  FIG. 5 . The valve is a simplistic representation of a butterfly valve, but any other suitable valve such as a sliding valve or an iris type valve may be used. The valve may be operated and/or controlled mechanically, electronically, hydraulically or pneumatically. Examples may be a pressure sensor in combination with an electronic control unit and electric motor, or an exhaust gas pressure actuated membrane directly connected with the valve via mechanical means.  
         [0017]     One of the cylinders  11  of the engine  10  is partially shown in  FIG. 6 . The piston  52 , the combustion chamber  53 , the intake valve  56  and the exhaust valve  54  are conventional, and there may be more than just one intake valve and/or exhaust valve per cylinder. The opening and closing of the exhaust valve and the intake valve follow a fixed timing pattern relative to the angle of the crankshaft (not shown) but may also be controlled by a variable valve timing arrangement. The valves can be actuated by any suitable means such as a camshaft  58  and rocker arm  60 , or via hydraulic or electronic arrangements (not shown).  
       INDUSTRIAL APPLICABILITY  
       [0018]     The internal combustion engine  10  uses the principle of iEGR via an iEGR arrangement  50  to improve emissions performance over a standard combustion process. iEGR can be achieved by either opening the intake valve  56  during the exhaust stroke of the piston  52  or by opening the exhaust valve  54  during the induction stroke of the piston. The principle used for this disclosure is the latter whereby during the induction stroke of the piston  52  part of the previously expelled exhaust gas is sucked back from the exhaust manifold  30  into the combustion chamber  53 .  
         [0019]     In conventional combustion cycles the exhaust valve  54  is opened mainly during the period wherein the piston  52  is performing its exhaust stroke. The period that the exhaust valve  54  is opened may not be identical to the period in which the piston is in the exhaust stroke, the valve opening period may be either shorter or longer, but is usually not much longer than the period of the exhaust stroke. Hence no, or an insignificant amount of, exhaust gas is sucked back into the combustion chamber  53 .  
         [0020]     In this particular iEGR system the exhaust valve  54  is open during at least part of the piston&#39;s  52  downward inlet stroke, so there is a substantial overlap in the periods that both the inlet  56  and exhaust valves are at least partially open. However, when the piston is approaching its top dead center (TDC) position, i.e., the end of the upward exhaust stroke, valve lifts must be reduced. One of the reasons for reducing valve lift is that if the exhaust valve is not recessed deeply into the cylinder head  14 , the clearance between the piston at TDC and the exhaust valve may not be sufficient to avoid interference. The exhaust valve may even have to be closed completely to avoid clashing with the piston. In that case, the exhaust valve is reopened after the piston has passed its TDC position to allow at least some of the previously expulsed exhaust gas to flow back into the combustion chamber  53  when the piston continues its downward induction stroke.  
         [0021]     Another variant uses a design that allows enough clearance between a partially opened exhaust valve  54  and the piston  52  at TDC, for example where the exhaust valve is recessed deeply into the cylinder head  14 . The exhaust valve therefore does not have to be closed completely and so rather than reopening the exhaust valve, the exhaust valve follows a delayed closure pattern. The non-closure of the exhaust valve during the TDC position of the piston has the added benefit of gaining a better advantage of the pumping effect of the piston.  
         [0022]     In addition to the various valve events and iEGR for controlling combustion, injection events are also crucial. Whereas traditionally one injection took place per cycle, nowadays it is common to have multiple injection events per cycle, e.g. split injections or pilot, pre- or post-injections in addition to a main injection. All these events influence the amount of exhaust gasses released at certain periods during a combustion cycle. Exhaust manifolds such as manifold  30  are designed to accommodate these exhaust gas pulses in a controllable manner so that the pulses do not interfere negatively with each other. However, interference problems may occur at several points in the speed range of an engine  10  as the manifold shape is a compromise to give an overall acceptable result across the operating range of the engine. A manifold with multiple branches that do not allow any fluid communication improves the pulsating action upon the turbine of the turbocharger and therefore the functioning of the turbocharger, but has the disadvantage that exhaust gas pressure pulses may cause the iEGR levels to be too high.  
         [0023]     For example, emissions legislation may regulate the maximum level of emissions over certain engine speeds, e.g., 1400 rpm. With two manifold branches that do not allow any fluid communication until proximal to the turbocharger, iEGR is required above 1400 rpm to meet the emissions regulation. Even though control systems such as waste gates are available to improve turbocharger efficiency throughout the speed range, the efficiency is still likely to vary. Especially at low speeds the turbocharger is less likely to easily supply a sufficient quantity of combustible air for an optimized combustion process. If exhaust gasses would flow back into the combustion chamber, the combustion process would be even less optimal and problems such as power loss and visible smoke may occur. Therefore it would in this example be very beneficial to be able to reduce the amount iEGR at low engine speeds.  
         [0024]     A passage such as passage  40  allows a control of the amount of iEGR by reducing exhaust gas pressure pulses via a pressure relief. Due to the nature of combustion cycles and the firing orders employed, the branches  32 ,  34  of the manifold  30  are out of synchronization with regards to pressure and pressure pulses.  
         [0025]     This translates into a flux situation wherein the branches alternate in low and high pressures without being equal except at crossover points where the pressure simultaneously rises in one branch whilst falling in the other branch. The different pressures allow some gas to flow from the branch with the higher gas pressure to the branch with the lower gas pressure. Therefore the pressure peaks are absorbed which then obviously leads to less iEGR if the exhaust valve is open during the intake stroke.  
         [0026]     If the passage is not variable or controllable, the passage is sized such that at all engine speeds the pressure relief from the first branch into the second branch and vice versa is performing to an overall acceptable level. However, more emphasis may be given to overcome a problem in a particular speed range such as the problem associated with low speed situations. If the passage is controllable it is likely that, to overcome the problems as indicated, the passage will be at a high degree of, or even maximum, opening at low engine speeds whilst it may be at a lower degree of, or minimum, opening at high engine speeds.  
         [0027]     Of course, it is to be understood that engines, subsystems, and especially manifolds with different characteristics combined with different operational demands may dictate different passage control regime.  
         [0028]     Although the preferred embodiments of this invention have been described herein, improvements and modifications may be incorporated without departing from the scope of the following claims.