Abstract:
A method and apparatus for boosting the pressure of the air charge to an internal combustion engine, which has an exhaust gas recirculation (EGR) system and a turbocharger. The EGR system is arranged to recirculate exhaust gas from an engine exhaust outlet passage to the engine air inlet passage. An exhaust gas bypass passage is arranged to divert exhaust gas that would otherwise reach the turbocharger&#39;s impeller. The engine has a single, unitary control valve with a valve inlet arranged to receive exhaust gas from the engine exhaust outlet passage, and three valve outlets. A first of the valve outlets provides exhaust gas to the EGR system for recirculation to the engine air inlet passage, a second of the valve outlets provides exhaust gas to the exhaust gas bypass passage and a third of the outlets provides exhaust gas to the impeller.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for boosting the pressure of the air charge to an internal combustion (IC) engine which has an exhaust gas recirculation (EGR) system, and in particular to such an engine having a combined EGR/turbocharger bypass control valve for controlling the amount of recirculated exhaust gas and the power of a turbocharger compressor. The invention is particularly although not exclusively for use in a diesel engine. 
     2. Related Technology 
     One way of boosting the pressure of the air charge to an IC engine is to use a turbocharger, which typically has a rotary compressor for compressing the intake air driven by a turbine wheel powered by engine exhaust gas. The result is that more air is sent into an engine&#39;s combustion chamber, increasing engine power. 
     When air is compressed, it is simultaneously heated. So, compressing engine intake air raises the temperature of air sent into the engine&#39;s combustion chamber. The raised air temperature increases the temperature of the combustion chamber and the surrounding engine components, which can increase thermal stress and reduce engine lifetime. Compressed intake air is often therefore cooled to increase the amount by which it can be compressed without detrimentally increasing combustion chamber temperature. This cooling can also generally increase the amount of air provided in the combustion chamber at a given intake pressure, as cool air is denser than hot air. Intake air cooking can therefore help to increase engine power. 
     Emission regulations are now beginning to dictate that many automotive engines mix intake air with recirculated exhaust gas, as this can reduce NOX (e.g. Nitrogen Dioxide etc.) emissions. NOX is formed in far higher quantities above certain combustion temperatures. Mixing recirculated exhaust gas with engine intake air can lower the combustion temperature and therefore reduce NOX formation. However, exhaust gas is hot. Like compressed intake air, it therefore benefits from cooling before it enters an engine&#39;s combustion chamber. In particular, cooling recirculated exhaust gas can increase the amount of exhaust gas that can be provided in the combustion chamber at a given intake pressure (e.g. improve mass flow). 
     Coolers for cooling compressed intake air are usually referred to as charge air coolers or intercoolers. Intercoolers can be cooled by engine coolant or other liquids, but are more commonly air cooled. An air cooled intercooler typically comprises an arrangement of tubes through which the compressed intake air can flow. For most car and light truck engines, intercoolers can provide sufficient cooling capacity without being inconveniently large and have relatively straightforward, robust and maintenance free designs. They are typically make from aluminum or plastics, as they only have to deal with relatively low temperatures (less than around 200° C.). 
     Coolers for cooling recirculated exhaust gas are usually referred to as Exhaust Gas Recirculation (EGR) coolers. An EGR cooler typically comprises a cylindrical shell containing one or more heat exchange tubes through which the exhaust gas can flow. Liquid coolant is passed through the shell around the tubes. The coolant is therefore in a heat exchange relationship with the exhaust gas and can cool it. Liquid cooling is used as it can typically provide greater cooling capacity than air cooling for a given heat exchange surface area. Thus, the heat exchange tubes can have a relatively large diameter and small surface area, which makes the EGR cooler tolerant to the build up of soot inside the tubes. EGR cooler are typically made from steel. One reason for this is that exhaust gas can be hot enough to damage other materials such as aluminum and plastics, but steel is more tolerant to high temperatures. 
     So, when it is desired to cool both engine intake air and recirculated exhaust gas, two separate coolers are conventionally provided; an intercooler and an EGR cooler. An example of such an arrangement is disclosed in patent document EP 1,138,928 A2. However, it is possible to use a combined EGR and inlet air cooler, for example as disclosed in U.S. Pat. No. 6,167,703 B1. 
     All such prior art systems entail a significant amount of cost, owing to the provision of conduits between the inlet and exhaust sides of the engine, and also valves to control the flow of exhaust gasses and the control systems associated with the operation of such valves. It is therefore desirable to minimize, as far as possible, the costs associated with such hardware. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the invention, there is provided a compressor and exhaust gas recirculation (EGR) apparatus for an internal combustion engine (ICE). The apparatus includes a turbine impeller, and exhaust gas inlet leading to the impeller for providing exhaust gas from one or more combustion chambers of an ICE to drive the impeller, an exhaust gas outlet for venting exhaust gas from the impeller, a compressor arranged to be driven by the impeller, an air inlet for supplying inlet air to the compressor, a compressed air outlet leading from the compressor for providing compressed air to one or more combustion chambers of an IC engine, an exhaust gas bypass passage for controlling the amount of exhaust gas used to drive the impeller, and EGR passage for recirculating exhaust gas from the exhaust gas inlet to the compressed air outlet, and a combined turbine impeller and EGR control valve arranged to receive exhaust gas from the exhaust gas inlet and to control the relative proportions of exhaust gas flowing to: the compressed air outlet via the EGR passage; the exhaust, gas outlet via the exhaust gas bypass passage; and the impeller. 
     According another aspect of the invention, there is provided an IC engine having one or more combustion chambers, and engine air inlet passage leading to the combustion chambers, an engine exhaust outlet passage leading from the combustion chambers, a turbocharger with a turbine impeller arranged to be driven by exhaust gas from the engine exhaust outlet passage and a compressor driven by the impeller for compressing air admitted to the engine air inlet passage, an EGR system arranged to recirculate exhaust gas from the engine exhaust outlet passage to the engine air inlet passage, and an exhaust gas bypass passage arranged to divert exhaust gas that would otherwise reach the impeller, a control valve with a valve inlet arranged to receive exhaust gas from the engine outlet passage, and three valve outlets, a first one of the valve outlets providing exhaust gas to the EGR system for recirculation to the engine air inlet passage, a second one of the valve outlets providing exhaust gas to the exhaust gas bypass passage and a third one of the outlets providing exhaust gas to the impeller. 
     Also according to the invention, there is provided a method of operating an IC engine, the engine including a turbocharger having a linked turbine impeller/compressor and an exhaust gas impeller bypass, an EGR system, an a combined turbine impeller and EGR control valve, said method comprising the steps of: 
     i) providing exhaust gas from the engine in order to drive the impeller and power the compressor; 
     ii) using the compressor to compress inlet air supplied to the engine; 
     iii) using the bypass to divert exhaust gas from reaching the impeller; 
     iv) using the EGR system to recirculate a portion of exhaust gas produced by the engine; 
     v) using the combined turbine impeller and EGR control valve to control both the amount of the exhaust gas diverted by the bypass and recirculated by the EGR system, and the amount of exhaust gas reaching the impeller. 
     The use of a combined turbine impeller and EGR control valve provides significant benefits. In particular, the arrangement permits a more efficient routing of conduits around an internal combustion engine for the exhaust gas recirculation from the outlet side of the engine to the inlet side of the engine. The turbocharger will normally be situated at a side of the engine convenient to receive from the engine the exhaust gas used to drive the impeller and to provide compressed inlet air to the engine. The use of the combined valve therefore allows the minimal use of conduits for exhaust gas recirculation which are in any event required to provide exhaust gas to the impeller and to provide compressed air to the engine. The invention therefore helps conserve space in the crowded environment of a typical internal combustion engine for a motor vehicle, as well as allowing a reduction in the complexity and number of components used in routing recirculated exhaust gas between the outlet and inlet sides of the engines. 
     The apparatus may advantageously include a housing which surrounds the impeller, compressor and control valve. This can help provide a compact unit which is easier to install during manufacture, and which has fewer components exposed to the harsh environment of a motor vehicle engine compartment. 
     The control valve, exhaust gas bypass passage and EGR passage are therefore preferably integrated within a unitary apparatus. 
     The EGR passage may be arranged to recirculate un-cooled exhaust gas from the exhaust gas inlet to the compressed air outlet, and the compressor is arranged to provide un-cooled compressed air to the compressed air outlet. By providing cooling separates from the turbocharger apparatus, the cooling may be provided at any convenient location with respect to the engine or engine compartment. 
     In a preferred embodiment of the invention, the control valve prevents exhaust gas from being recirculated whenever exhaust gas is allowed to bypass the impeller. This is useful in simplifying the design and operation of the combined control valve as exhaust gas recirculation is generally not desired at high engine speeds, when the turbocharger boost is significant and being limited by use of the bypass. 
     Alternatively, the control valve may control the proportions of exhaust gas being recirculated as exhaust gas bypasses the impeller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be further described, by way of example only, and with reference to the accompanying drawings, in which: 
         FIG. 1  is a block diagram of a conventional boosted IC engine utilizing a turbocharger unit with a conventional intercooler and conventional EGR system and EGR cooler. 
         FIG. 2  is a schematic illustration of a boosted IC engine according to a first embodiment; 
         FIG. 3  is a schematic illustration of a boosted internal combustion engine according to a second embodiment of the invention of the invention similar to the first embodiment in which the combined turbine impeller and EGR valve is integrated within the turbocharger unit; 
         FIG. 4  is a plot showing the proportion of recirculated exhaust gas in the total gasses admitted in the air inlet to the engine in the embodiments of the invention; and 
         FIG. 5  is a plot showing the proportions of exhaust gas directed by the combined turbine impeller and EGR valve to EGR and the turbine impeller bypass in the embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrate in schematic form a prior art turbocharged engine  1  utilizing exhaust gas recirculation (EGR). The engine  1  incorporates conventional compressed intake air cooling using a conventional air cooled intercooler  2  and conventional EGR cooling via an EGR cooler  4 . The coolers  2 ,  4  may be formed from aluminum or steel, and the EGR cooler  4  may employ engine coolant through coolant inlets and outlets (not shown) to cool recirculated exhaust gas. 
     A main engine exhaust gas passage  6  leads from an exhaust manifold  8  on the output side of one or more combustion chambers  10  of the engine  1 . The engine exhaust gas passage  6  conveys exhaust gas  12  from the exhaust manifold  8  towards a turbocharger exhaust gas inlet  13  that leads to a turbine impeller  14  of a turbocharger  16 . Exhaust gas  18  exits the turbocharger  16  via a turbocharger exhaust outlet passage  20 . An upstream EGR passage  22  branches from the main engine exhaust gas passage  6  to the EGR cooler  4 . The upstream EGR passage  22  forms together with the EGR cooler  4  and a downstream EGR passage  37  an EGR path between the outlet and inlet sides  8 ,  34  of the combustion chambers  10 . 
     The impeller  14  of the turbocharger  16  is coupled by a shaft  24  to a rotary compressor  26  for compressing engine intake air  28  received at a turbocharger air inlet  27  from an upstream air inlet passage  29 . The impeller  14  can therefore drive the rotary compressor  26  under power of exhaust gas inlet  13 . A turbocharger air outlet  31  from the compressor  26  is connected to a compressed air outlet passage  33  for conveying hot compressed engine intake air  30  to the intercooler  2 . Although not shown, a compressor bypass and bypass control valve may be provided between the upstream air inlet passage  29  and the compressed air outlet passage  33  in order to help regulate the compressed inlet air  30 . 
     The intercooler  2  is arranged to receive the hot compressed engine intake air  30  from the rotary compressor  26 , cool it, and provide cooled compressed air  36  to an engine air inlet passage  35  that leads to an inlet manifold  34  on the intake side of the combustion chambers  10 . 
     Similarly, the EGR cooler is arranged to receive a portion  38  of the hot exhaust gas  12  output by the combustion chambers  10  via the EGR branch passage  22 , cool it, and to provide cooled recirculated exhaust gas  40  to the downstream EGR passage  37  which meets the engine air inlet passage  35  at a confluence point or mixing point  32 , at which the cooled recirculated exhaust gas  40  is mixed with the cooled compressed air  36  prior to admission to the combustion chambers  10 . 
     An EGR regulator valve  42  is positioned between the EGR cooler  4  and the mixing point  32  to control the amount of cooled exhaust gas  40  that is recirculated to the mixing point  32  to control the amount of cooled exhaust gas  40  that is recirculated to the mixing point  32  and hence provided to the intake manifold  34  and combustion chamber  10 . 
     In order to control and limit the exhaust gas portion  25  provided to the impeller  14  and hence the power drawn from the total exhaust gasses  12 , a turbocharger exhaust gas bypass passage  44  is provided between a branch point  46  on the downstream exhaust gas outlet passage  20  and a confluence point  48  on the exhaust outlet nassae  20 . Flow of bypass exhaust gas  50  along the bypass passage  44  is controlled by a wastegate valve  52 . 
     One or more engine control units (ECU)  54  is arranged to control via control lines  56 ,  58  the operation the valves  42 ,  52  and hence the amount of recirculated exhaust gas  50  and the power boost provided by the turbocharger  16 . 
       FIG. 2  illustrates in schematic for a turbocharged engine  101  having EGR, according to a first embodiment of the invention. For convenience, features corresponding with those of the prior art engine  1  are indicated using the same reference numerals. 
     The invention differs from the prior art in that there is just one, unitary EGR/bypass control valve  60  for controlling the flow the engine exhaust gas  12  to the turbocharger impeller  14 , a turbocharger bypass  144 , and an exhaust gas recirculation path comprising an upstream EGR passage  122 , and EGR cooler  104  and a downstream EGR passage  137 . 
     The control valve  60  is a three-way rotary valve that has one inlet  61  into which the exhaust gas  12  from the main exhaust passage  6  flows. The valve has three outlets, a first one of which  62  is connected to the turbocharger exhaust gas inlet  13 , a second one of which  63  is connected to the upstream EGR passage  122  and a third one of which is connected to the bypass passage  144 , the latter joining the exhaust outlet passage  20  at confluence point  148 . The control valve  60  is configured to control the relative proportions of exhaust gas  125 ,  138 ,  150  supplied to the impeller  14 , the EGR system  122 ,  104 ,  137  and the exhaust gas bypass passage  144 . 
     As with the first embodiment 1, compressed air  30  from the turbocharger air outlet  31  from the compressor  26  is connected to a compressed air outlet passage  33  for conveying the hot compressed engine intake air  30  to the intercooler  2 . The cooled compressed air  36  in the engine air inlet passage  35  is then mixed with cooled recirculated exhaust gas  140  are mixed at a confluence point  132  upstream of the inlet manifold  34 . 
     The mixing point  132  comprises a venturi (not shown). More specifically, the mixing point  132  has a constricted throat for passing the cooled compressed engine intake air  36 . An inlet is provided in the side wall of the constricted throat for admitting the cooled exhaust gas  140 , after which the gas combination  36 ,  140  is provided to the inlet manifold  34  on the intake side of the combustion chambers  10 . 
     An engine control unit (ECU)  154  is arranged to control, via a control line  156 , the operation the control valve  60  and hence the amount of recirculated exhaust gas  140 , bypass exhaust gas  150  and exhaust gas  125  provided to the impeller  14 , and hence the power boost provided by the turbocharger  16 . 
     The amount of exhaust gas that is recirculated  138  to the mixing point  132  is controlled by varying the amount of exhaust gas that flows through the various valve outlets  62 ,  63 ,  64  of the control valve  60 . The amounts of both compressed intake air  30  and recirculated exhaust gas  138  that pass through, respectively the intercooler  2  and the EGR cooler  104  are varied depending on engine load, as shown in  FIG. 4 , which shows a plot of the proportion of recirculated exhaust gas  140  in the total gas combination  36 ,  140  provided to the inlet manifold  34 . As can be seen, the proportion is a maximum of about 40% at a minimum engine load of 10%, and declines to zero at an engine load of about 50%. 
       FIG. 5  shows how the control valve  60  under the control of the ECU  154  determines the proportions of exhaust gas flowing to the three valve outlets  62 ,  63 ,  64 . At a minimum engine load of 10%, about 20% of the exhaust gas  12  is provided to the EGR path  122 ,  104 ,  137 , none is provided to the bypass passage  144 , meaning than 80% flows  125  to the impeller  14 . 
     As engine load increases up to about 50%, there is still no exhaust gas provided to the bypass passage  144 , and the proportion of the exhaust gas  12  provided to the EGR path  122 ,  104 ,  137  drops steadily to zero, at which point all of the exhaust gas  12  flows  125  to the turbocharger impeller  14 . 
     Above 50% engine load, the amount of exhaust gas provided 125 to the bypass  144  increases in order to limit the speed of the turbocharger  16 , and hence the engine power, while none of the exhaust gas  12  is provided to the EGR path  122 ,  104 ,  137 . Above an engine speed of 90%, all the exhaust gas  12  bypasses the impeller  14 . 
       FIG. 3  shows a boasted internal combustion engine according to a second embodiment  201  of the invention. The second embodiment  201  differs from the first embodiment in having a unitary EGR/bypass control valve  160  that is integrated within a turbocharger unit  116 . Again for convenience, features corresponding with those of the prior art engine  1  or engine according to the first embodiment  101  are indicated using the same reference numerals as before. 
     As with the second embodiment  101 , the control valve  160  is a rotary valve which has a single valve inlet  161  that receives all the engine exhaust gas  12 , and three outlets  162 ,  163 ,  164  that convey varying proportions of exhaust gas  225 ,  238 ,  250  to the impeller  114 , an EGR passage  222 , and a turbocharger bypass passage  244 . These exhaust gas proportions  225 ,  238 ,  250  are controlled as described above with reference to  FIGS. 4 and 5  in order to control the amount of recirculated exhaust gas  238  and the power of a compressor  126  in the turbocharger unit  116 . 
     The second embodiment  201  of the invention results in significant benefits in terms of a reduction in the number of components and exhaust gas connections which need to be provided. Because the valve  160  is internal to the turbocharger  116 , so are the EGR passage  222 , the bypass passage  244  and the confluence points  232 ,  248 . 
     As with the first embodiment, the EGR confluence point  232  comprises a venturi (not shown) that has a constricted throat for passing un-cooled compressed engine intake air  130 . An inlet is provided in the side wall of the constricted throat for admitting the un-cooled exhaust gas  238 , after which the un-cooled gas combination  130 ,  238  is provided to a turbocharger compressed air outlet  131  and into an un-cooled compressed air passage  133  upstream of a combined intercooler  65  for cooling the mixture of compressed air  130  and exhaust gas  238 . The combined intercooler may employ engine coolant through coolant inlets and outlets (not shown) to cool the mixture of compressed air  130  and recirculated exhaust gas  238 . 
     The combined intercooler  65  provides a cooled gas mixture  136  into to an engine air inlet passage  135  that leads to the inlet manifold  34  on the intake side of the combustion chambers  10 . 
     The invention therefore also facilitates the use of a single combined intercooler  65 , rather than two separate coolers for the compressed air and recirculated exhaust gas, thus providing further benefits in terms of reduced part count and space consumed within a motor vehicle engine compartment. 
     The control valve  160 , EGR passage, bypass passage  244 , and EGR and bypass confluence points  232 ,  248  are preferably all housed within a turbocharger housing (not shown), for example a machined casting. More specifically, the control valve  160  may have a body cast in a casing of the turbocharger  116  around the impeller  114 . 
     In the illustrated embodiments  101 ,  201 , all the gas combination, that is, all the intake air and recirculated exhaust gas always passes through separate or combined coolers. However, in another embodiment (not shown), a bypass passage is connected from upstream of the EGR or combined cooler  104 ,  65  to a point downstream of the cooler  104 ,  65 . For example, in the second embodiment, such a bypass passage can be connected from between the mixing point  232  or the compressor outlet  131  and the air inlet passage  135  to the intake manifold  34  of the combustion chambers  10 . This bypass passage allows EGR or combined gas cooling to be bypassed during engine warm up and such like. 
     The engine  101 ,  201  of the described embodiments is preferably a diesel engine. However, the invention can equally be applied to a petrol (or “gasoline”) engine, Liquid Petroleum Gas (LPG) engine or such like. Similarly, the described engines  101 ,  201  are intended for automotive applications, usually for cars and light trucks. However, it may of course be used in a broad range of other applications, such as for an electrical generator. 
     In the foregoing description, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be evident, however, to one skilled in the art that the present invention may be practiced without using these specific details. In other instances, well-known methods and structures have not been described in detail so as not to unnecessarily obscure the present invention. 
     For example, it may in some applications of the invention be desirable to simultaneously direct some of the exhaust gas through the bypass while some gas is directed through the EGR system. Similarly the recirculated exhaust gas need not be directed through a venturi in the mixing of the recirculated exhaust gas and the inlet air. 
     Likewise, the described embodiments of the invention are only examples of how the invention may be implemented. Modifications, variations and changes to the described embodiments will occur to those having appropriate skills and knowledge. These modifications, variations and changes may be made without departure from the scope of the invention defined in the claims.