Patent Publication Number: US-2004055299-A1

Title: Method and device for operating an exhaust gas turbocharger

Description:
DESCRIPTION  
       [0001] 1. Technical Field  
       [0002] The invention relates to the operation of an exhaust gas turbocharger. It relates particularly to a method for operating an exhaust gas turbocharger according to the features of the preamble of patent claim 1, to a device for carrying out this method according to the features of the preamble of patent claim 5 and to an exhaust gas turbocharger having such a device.  
       [0003] 2. Prior Art  
       [0004] Exhaust gas turbochargers are used for the charging of internal combustion engines, a turbine, driven by the exhaust gas, of the exhaust gas turbocharger driving a compressor via a common shaft. The compressor sucks in, via an intake line, a gas, usually air or a mixture of air and of a gas, usually fuel gas and/or exhaust gas, and compresses this. Via a compressor line which is connected to the compressor downstream and is connected to an intake duct of the internal combustion engine, the compressed gas is supplied to combustion chambers of the internal combustion engine. With the aid of the compressed gas, more fuel can be burnt in the combustion chambers of the internal combustion engine than would be the case with normal aspirating engines, and therefore the performance of the internal combustion engine can be increased. The gas quantity supplied to the combustion chambers, together with other parameters, such as the setting and distribution of the fuel mixture and the ignition point, essentially codetermines the current performance of the internal combustion engine. This means that, for example, in the case of a load take-up during the starting or acceleration of the engine, as high a gas quantity as possible should be supplied and, during the throttling of the engine, the latter should, if possible, be operated with a reduced gas quantity. Typically, the gas quantity supplied to the combustion chambers of the internal combustion engine is regulated with the aid of a throttle valve which is arranged downstream of the compressor and upstream of the combustion chambers, as is, for example, shown in the article “New high efficiency high speed gas engine the 3MW class” in CIMAC Congress 1998 Copenhagen, page 1393, FIG. 9, or is described in MTZ Motortechnische Zeitschrift 50 [MTZ Engine Journal 50] (1989) 5, page 231, FIG. 7.  
       [0005] Just as, during the operation of the exhaust gas turbocharger, different pressures prevail in the intake line upstream of the compressor and in the flow-carrying lines downstream of the compressor, different pressures may also arise in the line segments upstream of the throttle valve and downstream of the throttle valve due to operation by means of the throttle valve. It has been shown, for example, that, during the throttling of the internal combustion engine, when the throttle valve is essentially closed, a vacuum prevails in the region downstream of the throttle valve, as compared with the pressure in the region upstream of the throttle valve. Under full load, then, the compressor usually delivers full power, so that the pressure in the region upstream of the throttle valve, that is to say between the compressor and the throttle valve, is normally also higher than the pressure upstream of the compressor in the intake line. In order, in the event of a sudden shedding of load, to eliminate these undesirable pressure conditions and obtain a rapid pressure reduction upstream of the throttle valve, various bypass lines have been proposed, which connect the region between the compressor and the throttle valve downstream of the compressor to the intake line upstream of the compressor and make it possible for the compressed gas to flow out of the region between the compressor and the throttle valve back into the intake line upstream of the compressor. Examples of such bypass lines are described in DE-A-28 23 067 and DE-A-197 28 850. So that the bypass line can be used in a controlled way, one or more bypass valves are provided in the bypass line. The control of these bypass valves functions essentially by pressure control. In this case, the pressure differences which occur are partially utilized directly by pressure valves, even pressures from the exhaust gas region of the system being taken into account. The control also partially takes place electronically, temperature, rotational speed and other data of the system also being taken into account in addition to the pressure data.  
       [0006] Even during acceleration out of the part load range into, for example, the full load range, unsatisfactory pressure conditions may be established in gas supply lines and exhaust gas discharge lines in the internal combustion engine/exhaust gas turbocharger system. For example, in the part load range with a small opening angle of the throttle valve, an unnecessarily high pressure occurs between the compressor and the throttle valve and reacts via the compressor on the turbine and brakes the latter. The braked turbine, in turn, causes a build-up of exhaust gas in the region between the combustion chambers and the turbine, thus reducing the efficiency of the internal combustion engine. In order to reduce this build-up and the associated high pressure upstream of the turbine, it is possible nowadays for the flow to pass around the turbine by means of a valve-controlled exhaust gas bypass line (waste gate). However, this leads to very sluggish acceleration of the exhaust gas turbocharger in the event of a load take-up. In order to achieve an improved response time of the sluggishly reacting turbocharger, it has been proposed, in U.S. Pat. No. 4,774,812 and DE-A-198 24 476, likewise to provide a bypass line for bypassing the compressor on the compressor side. In the part load range, a bypass flow is led from the intake line upstream of the compressor into the region between the compressor and the throttle valve downstream of the compressor, so that little gas to no gas at all flows through the compressor and the exhaust gas turbocharger idles, driven only by the turbine. The above-described braking action of the compressor is thereby eliminated. In the event of a sudden acceleration out of part load operation into, for example, full load operation, the bypass line is, by contrast, closed, and the compressor already running at relatively high speed can build up a corresponding boost pressure relatively quickly. Both in U.S. Pat. No. 4,774,812 and in DE-A-198 24 476, the control of the valves in the bypass line and in the line in which the compressor is arranged takes place electronically. For this purpose, the most diverse possible operating data of the turbocharger and the internal combustion engine, detected via sensors, are processed in a control unit and a corresponding control signal is transmitted to the valves in the two lines.  
       [0007] Presentation of the Invention  
       [0008] These electronic controls of the valves, such as are described in U.S. Pat. No. 4,774,812 and DE-A-198 24 476, are complicated and involve a high outlay and, because of the necessary sensors, are also costly.  
       [0009] The object of the invention is, therefore, to present a simple cost-effective method for operating an exhaust gas turbocharger, in which the charging efficiency of the exhaust gas turbocharger during the load take-up of the internal combustion engine is improved. Further, a technically very simple and therefore also cost-effective device for carrying out this method is presented.  
       [0010] This object is achieved by means of a method having the features of patent claim 1.  
       [0011] As in the methods described in U.S. Pat. No. 4,774,812 and DE-A-198 24 476, in the method according to the invention, a main flow of a gas is supplied via an intake line to a compressor of the exhaust gas turbocharger, is compressed in the compressor and is led via a compressor line into an intake duct of the internal combustion engine, the gas quantity transferred to combustion chambers of the internal combustion engine via the intake duct being regulated by means of a throttle valve arranged between the compressor and the combustion chambers. However, in contrast to the methods described in U.S. Pat. No. 4,774,812 and DE-A-198 24 476, according to the invention, when the vacuum occurs in the region downstream of the compressor between the compressor and the throttle valve, as compared with the pressure in the intake line upstream of the compressor, this vacuum is utilized in order to generate a bypass flow which flows around the compressor from its side located upstream to its side located downstream. In other words, the bypass flow is generated, utilizing the vacuum prevailing in the region between the compressor and the throttle valve, is branched off upstream of the compressor from the main flow led by the compressor and is returned to the main flow again downstream of the compressor between the compressor and the throttle valve.  
       [0012] By the vacuum being utilized in order to generate the bypass flow, this method can be carried out very simply and cost-effectively. The return of the bypass flow into the main flow upstream of the throttle valve allows an uncomplicated control in terms of the opening and closing of the bypass line.  
       [0013] By contrast, in the solution according to the invention, only the pressure ratio between the pressure p 1  in the intake line and the pressure p 2  in the region between the compressor and the throttle valve is relevant. During starting, and even during load take-up in the low load range, the pressure p 1  in the intake line is higher than the pressure p 2  between the compressor and the throttle valve, so that the bypass flow through the bypass line takes place in the direction of the main flow, around the compressor, toward the combustion chambers. This improves the charging efficiency not only during the starting of the internal combustion engine, but, above all, also considerably during load take-up in the low load range. In normal operation, the pressure p 2  between the compressor and the throttle valve is higher than the pressure p 1  in the intake line. In the solution according to the invention, therefore, irrespective of the pressure p 3  in the region downstream of the throttle valve, a flow pressure in the direction of the intake line always prevails during normal operation. In the solution according to the invention, therefore, a simple pressure-controlled, nonreturn valve can be adopted instead of a complicated control for changing flow directions.  
       [0014] If the bypass flow is branched off from the main flow in the intake line downstream of a flowmeter, evidential data on the mass flow, which are important for setting the fuel mixture, are obtained via the flowmeter even with regard to the flow around the compressor. If the bypass flow is returned into the main flow again in the region of the compressor line, the exhaust gas turbocharger can be separated from the internal combustion engine in a very simple way, thus reducing the assembly costs.  
       [0015] This method can be carried out in a very simple way by means of a device according to the invention which can be connected to a conventional system consisting of an internal combustion engine and of an exhaust gas turbocharger. The conventional system of internal combustion engine and exhaust gas turbocharger has an exhaust gas turbocharger with a compressor driven via a turbine. Said compressor is flow-connected upstream to an intake line and downstream to a compressor line. The compressor line can be connected to an intake duct of the internal combustion engine to form a flow line, a throttle valve being provided in the flow line. The device according to the invention comprises a bypass line which, in the assembled state, is connected on its first side to the intake line upstream of the compressor and with its second side to the flow line between the compressor and the throttle valve. The bypass line is in this case designed in such a way that it allows only a flow around the compressor from the compressor side located upstream to the compressor side located downstream. This can be made possible in the simplest and most cost-effective way by the bypass line having provided in it at least one regulating element, for example a nonreturn valve, which allows a flow from the compressor side located upstream to the compressor side located downstream, but prevents a flow in the opposite direction. The nonreturn valve is designed as a pressure-sensitive valve and is acted upon from one side by the pressure p 1  and from the other side by the pressure p 2 . This makes it possible to have a very simple automatically resulting control which is not susceptible to faults and moreover is still highly cost-effective. Possibilities for the configuration of such a nonreturn valve are, for example, a spring-assisted ball valve or disk valve. Depending on the geometry of the bypass line, it may be expedient to provide more than one nonreturn valve.  
       [0016] The device according to the invention may be provided in new turbochargers, but it is also suitable for the retrofitting of existing exhaust gas turbochargers.  
       [0017] If an exhaust gas turbocharger for charging an internal combustion engine is already provided with a device according to the invention, this is highly advantageous for assembly. The bypass line is then advantageously connected to the compressor line downstream of the compressor, so that, during assembly, it does not have to be connected separately to the intake duct of the internal combustion engine. Admittedly, it is also conceivable that the second side of the bypass line is not connected to the compressor line of the exhaust gas turbocharger, but is designed for connection to the intake duct of the internal combustion engine. In this case, the throttle valve must be arranged in the intake duct of the internal combustion engine, and, during assembly, the bypass line must also be connected upstream of the throttle valve to the intake duct of the internal combustion engine.  
       [0018] Internal combustion engines equipped with an exhaust gas turbocharger and having a device according to the invention achieve a higher charging efficiency both during starting and, above all, during any load take-up from idling, when the throttle valve is opened rapidly, and, as long as the pressure p 2  is lower than the pressure p 1 , the still slowly rotating compressor acts as a throttle.  
       [0019] Further preferred embodiments are the subject matter of further dependent patent claims. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
     [0020] The subject of the invention is explained in more detail below with reference to a preferred exemplary embodiment illustrated in the accompanying drawing in which, purely diagrammatically:  
     [0021]FIG. 1 shows an exhaust gas turbocharger with a device according to the invention, connected to an internal combustion engine;  
     [0022]FIG. 2 shows part of a compressor side of an exhaust gas turbocharger in section along its longitudinal axis, with an integrated bypass line; and  
     [0023]FIG. 3 shows a further embodiment of an exhaust gas turbocharger with an integrated bypass line, in an illustration according to FIG. 2. 
    
    
     [0024] The reference symbols used in the drawings and their significance are listed in summary in the list of reference symbols. The embodiment described is one example of the subject of the invention and has no restrictive effect.  
     [0025] Ways of Implementing the Invention  
     [0026]FIG. 1 shows an exhaust gas turbocharger  10  with a turbine  12  and with a compressor  14 , the turbine  12  and the compressor  14  being arranged on a common shaft  16 . An exhaust gas line  22  leads from an internal combustion engine  20  having combustion chambers  21  to the turbine  12 . Exhaust gases are supplied to the turbine via the exhaust gas line  22  and drive the turbine  12  so that the compressor  14  also begins to operate via the common shaft  16 . Exhaust gases are discharged downstream of the turbine  12  via a discharge line  24 .  
     [0027] The compressor  14  draws in air under the pressure p 1  via an intake line  26  arranged upstream. As indicated by the line  27  depicted by dashes, it is also possible to branch off part of the exhaust gas from the discharge line  24  by means of a connecting line and admix it, upstream of the compressor  14 , to the air sucked in via the intake line. A fuel gas may also be admixed to the sucked-in air from a fuel gas container  29   a ,  29   b ,  29   c ,  29   d . This admixing may take place both upstream  29   a  of the compressor  14  and at various locations downstream  29   b ,  29   c ,  29   d  of the compressor (in each case indicated by dashes). Sucked-in air and also an air/exhaust gas and air/fuel gas mixture or a mixture of air, fuel gas and exhaust gas are gases, and for this reason only gas will continue to be referred to. The sucked-in gas is led via the compressor  14 , is compressed by the latter and is fed downstream into a compressor line  28 . The compressor line  28  is connected to an intake duct  32  of the internal combustion engine  20  with the aid of a flanged connection  30 . The compressor line  28  and the intake duct  32  together form a flow line  34  in which a throttle valve  36  is arranged. Although this is not generally customary, it is admittedly also conceivable that the throttle valve  36  is arranged in the compressor line  28  of the exhaust gas turbocharger  10  instead of in the intake duct  32  of the internal combustion engine  20 . In the example shown here, a charge air cooler  38  is arranged downstream of the throttle valve  36 . Downstream of the charge air cooler  38 , the intake duct  32  is connected to the combustion chambers  21  of the internal combustion engine  20 .  
     [0028] The exhaust gas turbocharger  10  has a device  40  according to the invention with a bypass line  42  which is connected on its first side  44  to the intake line  26  upstream of the compressor  14  and with its second side  46 , downstream of the compressor, to the compressor line  28  between the compressor  14  and the throttle valve  36 . It is, of course, also conceivable to connect the second side  46  of the bypass line  42  between the compressor  14  and the throttle valve  36  to the intake duct  32 , instead of to the compressor line  28 , as is indicated by the dashed line  43 . The bypass line  42 ,  43  is equipped with simple nonreturn valves  48  which allow only a flow around the compressor  14  from the upstream side to the downstream side of the compressor  14 . The nonreturn valves  48  open automatically when the ambient pressure p 1  becomes higher than the pressure p 2  prevailing in the region between the compressor  14  and the throttle valve  36 . This occurs whenever the throttle valve  36  is opened completely, such as, for example, during the starting of the internal combustion engine  20 ; but, above all, also highly efficiently in the case of a load take-up from idling, because the slowly rotating compressor  14  then acts as a throttle.  
     [0029] Thus, whenever the pressure p 1  in the intake line  26  is higher than the pressure p 2  in the region between the compressor  14  and the throttle valve  36 , the nonreturn valves  48  open due to the vacuum p 2  downstream of the compressor  14 , and a bypass flow B occurs, which is branched off from the main flow A upstream of the compressor  14 . The bypass flow B diverted from the main flow A is led through the bypass line  42 ,  43  from the upstream side around the compressor  14  to the downstream side of the compressor  14  and is returned into the main flow A upstream of the throttle valve  36  and downstream of the compressor  14 . If a flowmeter  18  is provided in the intake line  26 , it is advantageous to branch off the bypass flow B from the main flow A in the intake line  26  downstream of the flowmeter  18 . Evidential data on the mass flow is thereby obtained via the flowmeter  18  even in the case of the flow around the compressor.  
     [0030] It is, of course, conceivable to provide only one nonreturn valve  48  instead of the plurality of nonreturn valves  48  or to provide, instead of the nonreturn valve or nonreturn valves  48 , one or more other regulating elements which allow the flow to pass through the bypass line  42 ,  43  only in the direction from the upstream side of the compressor  14  to the downstream side of the latter.  
     [0031]FIG. 2 shows part of the compressor side of an exhaust gas turbocharger  10  in section along the longitudinal axis  51  of the latter, in which the device  40  according to the invention is integrated into the casing  50  of the exhaust gas turbocharger  10 . The compressor wheel  53 , which is arranged with its hub  54  on the shaft  16 , acts as the compressing element  52  in the compressor  14 . The moving blades  56  of the compressor wheel  53  are fastened to the hub  54 . Air, depicted as the main flow A, is sucked in via the intake line  26 , which is connected to the surroundings  58 , and is led via the compressor wheel  53  and a diffuser  60  into a spiral casing  62  of the compressor  14 , said spiral casing being an integral part of the compressor line  28 . In this case, the air is compressed from the ambient pressure p 1  to the pressure p 2 . A connecting orifice  64  in the spiral casing  62  connects the spiral flow duct in the spiral casing  62  to a cavity  66  in the compressor-side part of the casing  50  of the exhaust gas turbocharger  10 . The cavity  66  is connected to the surroundings  58  via a valve orifice  68  which is closed, by means of a flap  70  designed, in interaction with the valve orifice  64 , as a nonreturn valve  48 , as long as the ambient pressure p 1  is lower than the pressure p 2  in the spiral casing  62 . If, however, a vacuum p 2  prevails in the spiral casing  62 , as compared with the ambient pressure p 1 , as occurs precisely in the case of a rapid load take-up from idling, then the flap  70  opens counter to the force of a spring  72 , for example into the position  74  illustrated by dashes, and ambient air flows through the cavity  66  of the casing  50  until the pressures p 1  and p 2  are equal again or the pressure p 2  is higher than the ambient pressure p 1  again. The cavity  66  in the casing  50  thus serves, in this case, as a bypass line  42  for bypassing that element in the compressor  14  via which the sucked-in gas, air, is compressed. The cavity  66  thus serves for bypassing the compressor wheel  52  from the upstream side with the ambient pressure p 1  to the downstream side with the pressure p 2 .  
     [0032]FIG. 3 shows a second example of such a bypass line  42  integrated in the casing  50  of the exhaust gas turbocharger  10 . The construction is basically the same as in FIG. 2. However, the cavity  66  serving as a bypass line  42  is connected by means of the nonreturn valve  48 , instead of directly to the surroundings  58 , to a line  76  which, in turn, can be flow-connected (not illustrated) to the surroundings  58 , to the intake line  26  and/or, for example, to the fuel gas container  29   a  and/or the connecting line  27 .  
     [0033] If the bypass line  42  is integrated in the casing  50  of the exhaust gas turbocharger  10 , then other nonreturn valves  48  or other mechanisms having the same action may be used instead of the simple flap device  70  with spring  72 . So as not to influence the flow conditions in the spiral casing  62  adversely, the connecting orifice  64  in the spiral casing  62  may also be provided with a corresponding valve. The cavity  66  may also be designed as a duct incorporated in the casing and optimized in terms of flow, and the nonreturn valve or nonreturn valves may then be designed, for example, as ball valves. As described in FIG. 1, however, a bypass line  42  not integrated into the casing may also be used, this being especially suitable, in particular, for the retrofitting of existing systems.  
     [0034] List of Reference Symbols  
                                                      10   Exhaust gas turbocharger           12   Turbine           14   Compressor           16   Shaft           18   Flowmeter           20   Internal combustion engine           21   Combustion chamber           22   Exhaust gas line           24   Exhaust gas discharge line           26   Intake line           27   Connecting line           28   Compressor line           29a, 29b,   Fuel gas container           29c, 29d           30   Flanged connection           32   Intake duct           34   Flow line           36   Throttle valve           38   Charge air cooler           40   Device           42, 43   Bypass line           44   First side           46   Second side           48   Regulating element, nonreturn valve           50   Turbocharger casing           51   Longitudinal axis of the exhaust gas turbocharger           52   Compressing element           53   Compressor wheel           54   Hub           56   Moving blade           58   Surroundings           60   Diffuser           62   Spiral casing           64   Connecting orifice           66   Cavity           68   Valve orifice           70   Flap           72   Spring           74   “Open” position           76   Line