Abstract:
The invention relates to an internal combustion engine, especially of a motor vehicle, which comprises an air path for intake air in which a mechanically driven charge unit ( 20 ), especially a compressor, which can be connected and disconnected by means of a coupling ( 36 ), an exhaust gas turbocharger ( 18 ), an intake pipe ( 32 ), connected to air inlets of a cylinder block ( 10 ) of the internal combustion engine, and a charge cooler ( 34 ) are mounted. One pressure outlet ( 35 ) of the mechanically driven charge unit ( 20  is directly connected to the intake pipe ( 32 ) and one pressure outlet ( 24 ) of the exhaust gas charger ( 18 ) is connected to an intake inlet ( 28 ) of the mechanically driven charge unit ( 20 ). The pressure outlet ( 24 ) of the exhaust gas charger ( 18 ) is connected to the intake inlet ( 28 ) of the mechanically driven charge unit ( 20 ) via an on-off butterfly valve ( 26 ) and upstream of said on-off butterfly valve ( 26 ) to the intake pipe ( 32 ) via a load butterfly valve ( 30 ). The charge cooler ( 34 ) is integrated into the intake pipe ( 32 ) to give an intake/charge cooler module.

Description:
This is a U.S. national stage of application No. PCT/EP2005/013730, filed on Dec. 20, 2005. Priority is claimed on that application and on the following application: 
     Country: Germany, Application No.: DE 10 2005 004 122.1 Filed: Jan. 28, 2005 
     BACKGROUND OF THE INVENTION 
     The invention concerns an internal combustion engine, especially of a motor vehicle, with an air path for intake air, in which are installed a mechanically driven supercharger, especially a compressor, which can be connected and disconnected by means of a coupling; an exhaust gas turbocharger; an intake pipe connected with the air intakes of a cylinder block of the internal combustion engine; and a charge air cooler. A pressure outlet of the mechanically driven supercharger is directly connected to the intake pipe, and a pressure outlet of the exhaust gas turbocharger is connected to a suction intake of the mechanically driven supercharger. The invention also concerns a method for operating this internal combustion engine. 
     U.S. Pat. No. 4,903,488 discloses an internal combustion engine with an air path for intake air, in which a compressor, an exhaust gas turbocharger, and a throttle valve are arranged, where an outlet of the compressor is connected with an inlet of the exhaust gas turbocharger, and the throttle valve is arranged downstream of the exhaust gas turbocharger. A compression throttle valve is arranged in an air passage that bypasses the compressor, and this valve optionally closes exclusively this air passage that bypasses the compressor. 
     DE 32 27 459 A1 discloses a system of this general type for supercharging an internal combustion engine. It comprises a combination of an exhaust gas turbocharger with a compressor that is mechanically driven by the shaft of the internal combustion engine. This compressor provides the supercharging during start-up and in the lower speed ranges. It is switched off when a sufficient supercharging pressure of the turbocharger is reached and switched back on when this pressure drops. A pressure outlet of the mechanical compressor opens directly into an intake pipe of the internal combustion engine. In a preferred embodiment, all the charge air is passed from the exhaust gas turbocharger through the mechanically driven compressor, which, during idling, is fully open for the full delivery of the charge air. As long as the exhaust gas turbocharger does not deliver sufficient charge air due to the engine speed being too low, i.e., during start-up and in the low engine speed range, the internal combustion engine is supercharged by the mechanical compressor. When the exhaust gas turbocharger reaches sufficient output in the higher engine speed ranges, the mechanical compressor runs idle, i.e., in the engine speed ranges in which the outputs of the mechanical charger would drop. Alternatively, a system with a bypass line for the compressor is proposed, where the bypass line is closed by a valve during the operation of the compressor. This valve is opened as soon as the compressor is no longer mechanically driven, i.e., in the higher load ranges, in which the exhaust gas turbocharger can make a sufficiently high charge pressure available. 
     SUMMARY OF THE INVENTION 
     The objective of the invention is to improve an internal combustion engine of the type described above with respect to its design, assembly, and manner of operation. 
     To this end, the invention provides that, in an internal combustion engine of the aforementioned type, the pressure outlet of the exhaust gas turbocharger is connected to the suction intake of the mechanically driven supercharger via an on-off butterfly valve and to the intake pipe via a load control butterfly valve upstream of the on-off butterfly valve, where the charge cooler is integrated in the intake pipe to form an intake/charge cooler module. 
     This has the advantage that, due to the special arrangement of the superchargers in the air path to the intake pipe and the incorporation of the charge cooler in the intake pipe, an otherwise necessary throttle valve can be eliminated, and at the same time a very small volume is present between the mechanically driven supercharger and the combustion chamber, so that there is a significant improvement in the dynamic behavior. 
     It is advantageous for the on-off butterfly valve to be designed in such a way that, in the completely closed state, it essentially seals the air path to the suction intake of the mechanically driven supercharger against a secondary air flow through the mechanically driven supercharger. 
     In accordance with the invention, in a method of the aforementioned type, it is provided that, in those operating states of the internal combustion engine in which the instantaneous torque demand can be produced by the exhaust gas turbocharger, the on-off butterfly valve is brought into its completely closed position, the mechanically driven supercharger is deactivated, and the load is controlled by means of the load control butterfly valve and/or by adjustment of the turbocharger, and in those operating states of the internal combustion engine in which the instantaneous torque demand exceeds the maximum torque that can be produced by the exhaust gas turbocharger, the on-off butterfly valve is brought into its completely open position, the mechanically driven supercharger is activated, and the load control butterfly valve is closed to the extent necessary to reach the torque demand. 
     This has the advantage that the load control butterfly valve mounted in the intake/charge cooler module has a dual function, namely, on the one hand, it has the function of a conventional throttle valve in those operating states in which the exhaust gas turbocharger can make available the torque demanded of the internal combustion engine, and, on the other had, it has the function of a recirculated air control valve for a bypass line of the mechanically driven supercharger at high instantaneous torque demands that exceed the capacity of the exhaust gas turbocharger, so that an additional power control element in the air path can be dispensed with. 
     It is effective for the on-off butterfly valve to be closed during idling and in the lower partial-load range and to be completely open in all other operating states. 
     The invention is explained in greater detail below with reference to the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a preferred embodiment of an internal combustion engine of the invention. 
         FIG. 2  is load-speed diagram. 
         FIG. 3  is a graphic representation of the operation of the internal combustion engine of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a preferred embodiment of an internal combustion engine of the invention. It comprises an engine block  10 , an exhaust system  12 , and an air path for the intake of combustion air or fresh air. The following are mounted in the air path: an air filter  14 , a compressor  16  of an exhaust gas turbocharger  18 , and a mechanically driven supercharger  20 , for example, a compressor. A turbine  22  of the exhaust gas turbocharger  18  is installed in the exhaust system  12  of the internal combustion engine. A pressure outlet  24  of the exhaust gas turbocharger  18  is connected with a suction intake  28  of the mechanically driven supercharger  20  via an on-off butterfly valve  26 . Upstream of the on-off butterfly valve  26 , the pressure outlet  24  of the exhaust gas turbocharger  18  is connected with an intake pipe  32  via a load control butterfly valve  30 . In addition, a charge cooler  34  is provided, which is integrated in the intake pipe. The charge cooler  34  and intake pipe  32  together form an intake/charge cooler module. A pressure outlet  35  of the mechanically driven supercharger  20  is directly connected with the intake pipe  32 . This results in a very small volume between the mechanically driven supercharger  20  and the combustion chambers in the engine block  10 , and this in turn produces significant improvement of the dynamic behavior. The mechanically driven supercharger  20  is connected with a crankshaft  38  of the internal combustion engine by a coupling  36  and is mechanically driven by it. Depending on the operating state of the internal combustion engine, the mechanical connection between the mechanically driven supercharger  20  and the crankshaft  38  is produced or broken by the coupling  36 . Pressure transducers  78  for measuring the pressure in the air path and the intake pipe  32  are installed as part of the engine speed control system. 
     The term “on-off butterfly valve” means that this valve has only two different positions, namely, either completely open or completely closed (on-off valve). There is no provision for intermediate positions. The on-off butterfly valve  26  is designed in such a way that in its completely closed position, the air path to the suction intake  28  of the mechanically driven supercharger  20  is closed essentially flow-tight, so that secondary air flow through the mechanically driven supercharger  20  is prevented. 
     The compressor of the exhaust gas turbocharger  18  draws air in through the air filter  14  and, depending on the energy made available by the turbine  22  of the exhaust gas turbocharger  18 , conveys the air mass flow to the load control butterfly valve  30 . The power output of the exhaust gas turbocharger  18  and the turbine  22  is automatically controlled by a waste gate and possibly a variable turbine geometry of the exhaust gas turbocharger  18 . The load control butterfly valve  30  is flange-mounted directly on the intake/charge cooler module  32 ,  34 . 
       FIG. 2  shows a load-speed diagram, in which the engine torque Md is plotted on the vertical axis  40 , and the engine speed n mot  is plotted on the horizontal axis  42 . One graph  44  characterizes the maximum attainable engine torque as a function of the engine speed n mot  when the internal combustion engine is operated as a naturally aspirated engine (aspirated engine full load). One graph  46  characterizes the maximum attainable engine torque as a function of the engine speed when the internal combustion engine is operated with the turbocharger (turbocharger full load). One graph  48  characterizes the maximum attainable engine torque as a function of the engine speed when the internal combustion engine is operated with the turbocharger and mechanically driven supercharger  20  (supercharger and compressor full load). One graph  50  characterizes the maximum engine torque that can be delivered by the engine (maximum load). One trace  52  over the points  0  to  9  in the load-speed diagram of  FIG. 2  illustrates an example of a curve of torque versus speed. 
       FIG. 3  graphically illustrates for the points  0  to  9  of the trace  52  an angular position  54  of the load control butterfly valve  30  between a completely closed position  56  and an unthrottled position  58 , a pressure  60  after the compressor  16  of the exhaust gas turbocharger  18  between a minimum value  62  and a maximum value  64 , a position  66  of the on-off butterfly valve  26  between the position “off” or “completely closed”  68  and the position “on” or “completely open”  70 , and a state  72  of the coupling  38  between “closed” or “a mechanical connection between crankshaft  36  and mechanically driven supercharger  20  is produced”  74  and “open” or “a mechanical connection between crankshaft  38  and mechanically driven supercharger  20  is broken”  76 . 
     The trace  52  shows a curve of engine torque Md and engine speed n mot , where, from point  0  to point  1  of the trace  52 , the required engine torque rises, and from point  1  to point  4  of the trace  52 , the required engine torque Md jumps suddenly to a value that is above the naturally aspirated engine full load  44  and the turbocharger full load  46 . From point  4  to point  6  of the trace  52 , the required engine torque remains above the turbocharger full load  46  and on the maximum load  50 . At point  6 , the required engine torque falls below the turbocharger full load  46 , and at point  8  the required engine torque finally falls below the naturally aspirated engine full load  44 . This curve of the trace from point  1  to point  9  represents a typical start-up operation with a motor vehicle that has the internal combustion engine of the invention as its power plant, with the required engine torque being determined by a driver. 
     As is immediately apparent from a comparison with  FIG. 3 , load control takes place from point  0  to point  2  of the trace  52  by means of the load control butterfly valve  30 . During this stage, the on-off butterfly valve  26  is completely closed to prevent secondary air flow via the mechanically driven supercharger  20 . From point  2  to point  3  of the trace  52 , load control takes place by means of the turbine  22  of the exhaust gas turbocharger  18  (by a waste gate, variable turbine geometry, etc.). 
     When the required engine torque exceeds the turbocharger full load  46  at point  3  of the trace  52 , the on-off butterfly valve  26  is opened completely, the mechanically driven supercharger  20  is activated by connecting the coupling  36  (graph  72  jumps from “open”  76  to “closed”  74 ), and the load control butterfly valve  30  is closed until point  4  is reached. In this range, the load control butterfly valve  30  operates as a recirculated air butterfly valve of the mechanically driven supercharger  20 . The more completely the load control butterfly valve  30  is closed, the smaller is the mass flow flowing away from the intake pipe  32  via the load control butterfly valve  30 , i.e., the charge pressure increases with the closing of the load control butterfly valve  30  when the mechanically driven supercharger  20  is connected. 
     From point  4  to point  5 , the load control butterfly valve  30  is completely closed, the on-off butterfly valve  26  is opened, and the coupling  36  of the mechanically driven supercharger  20  is closed. As a result, the mass flow delivered by the compressor  16  of the turbocharger  18  is conveyed completely through the mechanically driven supercharger  20  and compressed to the maximum extent. Both superchargers operate with a maximum compression ratio. 
     At point  5 , the maximum attainable engine torque (graph  50 ) is reached. From point  5  to point  6 , the intake pipe pressure is adjusted to the level necessary for the maximum engine torque by opening the load control butterfly valve  30 . At point  6 , the load control butterfly valve  30  is completely opened, and the mechanically driven supercharger  20  is shut off by opening the coupling  36  and closing the on-off butterfly valve  26 . Starting at point  6 , the turbocharger  18  can produce the charge pressure necessary for the maximum engine torque solely via the waste gate, the variable turbine geometry, etc. Starting at point  7 , the charge pressure necessary for the required engine torque is reduced by the position of the waste gate, variable turbine geometry, etc., until the minimum charge pressure is reached at point  8  with the load control butterfly valve  30  completely open. To reduce the required torque further to point  9 , the load control butterfly valve  30  is then closed as far as necessary. 
     When the torque demand by the driver is low, the on-off butterfly valve  26  is closed, the coupling  36  of the mechanically driven supercharger  20  is opened, and the exhaust gas turbocharger  18  is adjusted via the waste gate, variable turbine geometry, etc., in such a way that as little charge pressure as possible is produced. Load control occurs here as in a naturally aspirated engine: the farther the load control butterfly valve  30  is opened, the higher is the air mass flow supplied to the engine. If the torque demand rises above the maximum torque that can be produced in the naturally aspirated engine mode (point  2  of the trace  52 ), then the air mass flow is increased by adjusting the turbine  22  of the exhaust gas turbocharger  18  (waste gate, variable turbine geometry, etc.) and thus increasing the intake pipe pressure, so that the required engine torque can be reached. The load control butterfly valve  30  remains open during this process. If a still higher torque is demanded (point  3  of trace  52 ), then the coupling  36  of the mechanically driven supercharger  20  is closed, and the on-off butterfly valve  26  is completely opened. The charge pressure in the intake pipe  32  is increased by closing the load control butterfly valve  30 . 
     Switching between dual charging and sole operation with the exhaust gas turbocharger  18  by cooperation between the load control butterfly valve  30  and the on-off butterfly valve  26  makes it possible, due to the dual function of the load control butterfly valve  30 , on the one hand, as a conventional throttle valve at low engine torques below the intake pipe full load  44  and, on the other hand, as a recirculated air butterfly valve during operation above the turbocharger full load  46 , to dispense with a throttle valve that would otherwise be necessary instead of the on-off butterfly valve  26 .