Abstract:
A method for regenerating a soot-laden particle filter in the exhaust gas train of a diesel engine in a vehicle, wherein the engine is equipped with a fuel injection system having an injection valve for each cylinder and an exhaust braking device including a butterfly valve in the exhaust gas train upstream of the particle filter. An exhaust braking phase is initiated by closing the butterfly valve, thereby causing hot exhaust gas to be compressed upstream of the butterfly valve. Regeneration of the particle filter is then initiated by injecting diesel fuel into the cylinders substantially after the respective pistons pass top dead center, and allowing the hot exhaust gas mixture containing unburned fuel and air to flow past the butterfly valve so that the mixture ignites the soot and then supports combustion of the soot, thereby regenerating the particle filter.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a method for the regeneration of a particle filter installed in the exhaust gas train of a vehicular diesel engine and partially loaded with separated soot particles, where the diesel engine is equipped with an exhaust brake device, to which a butterfly valve in the exhaust gas train upstream of the regeneration site belongs, and with a fuel injection system with an injection valve for each cylinder. 
         [0003]    2. Description of the Related Art 
         [0004]    In utility vehicles with diesel engines, particle filters are provided in the exhaust gas trains to satisfy the legally imposed exhaust gas regulations. Oxidation catalysts are installed upstream of the particle filters to increase the concentration of NO x  in the exhaust gas, and in some cases SCR catalysts can be installed downstream. These particle filters are loaded to a greater or lesser extent with the soot separated from the exhaust gas. At sufficiently high exhaust gas temperatures (&gt;350° C.), the soot is oxidized almost continuously. If the exhaust gas temperatures are not high enough, it is known that thermal regeneration can be initiated and supported by the injection of a certain amount of fuel into the exhaust gas train upstream of the particle filter to be regenerated. The diesel fuel, serving as an HC carrier, is injected here by means of specially provided fuel metering devices. The heat released during the oxidation of the vaporized hydrocarbons (HC) in the exhaust gas train heats the particle filter to the ignition temperature of the collected soot. An open and closed-loop electronic control system, which is usually very complex, ensures that suitable starting conditions are provided for this type of regeneration. Especially in the case of vehicles like route buses and delivery trucks, which are operating under non-steady-state conditions most of the time, this known method of initiating the regeneration of soot-loaded particle filters usually results in the consumption of comparatively large amounts of fuel, which, as a result of increasing fuel prices, is strongly reflected in vehicle operating costs. 
       SUMMARY OF THE INVENTION 
       [0005]    It is therefore an object of the invention to improve the regeneration method of the general type in question so that it can be implemented more simply in terms of design and apparatus and also so that, upon its application, the extra amount of fuel consumed is less than that of the previously mentioned known regeneration methods. 
         [0006]    According to the invention, the particle filter is regenerated during an exhaust braking phase by injecting diesel fuel into the cylinders substantially after the respective pistons pass top dead center, thereby creating a hot gas mixture containing unburned fuel and air. The hot gas mixture is allowed to flow past the butterfly valve so that the mixture ignites the soot and then supports combustion of the soot, thereby regenerating the particle filter. 
         [0007]    In contrast to conventional methods, the inventive method allows the soot particle-loaded particle filter to be regenerated only during the times that the exhaust brake is operating. This means that the inventive method can be applied only in conjunction with diesel engines which have an exhaust brake device, to which a butterfly valve installed in the exhaust gas train upstream of the particle filter and either upstream or downstream of the turbine of an exhaust gas turbocharger also belongs. The butterfly valve is usually in the pass-through position, but it is switched into its blocking position during a normal exhaust braking phase, as a result of which the gas backed up in the blocked-off area of the exhaust gas line cooperates with the pistons in the individual engine cylinders to increase the braking power. So that the engine does not stall out during the braking process, however, the butterfly valve is not completely closed, or a small bypass channel, located in the area of the butterfly valve and passing around it, is opened by a valve, so that a small amount of the gas can flow from the backed-up area into the following section of the exhaust gas line. Since the butterfly valve is closed when the driver releases the fuel throttle, almost no fuel is admitted for combustion. As a result, the exhaust gas is little more than the air ingested during the intake stroke. 
         [0008]    The previously described specific relationships which are present during an exhaust braking phase, in conjunction with the fuel injection system inside the engine, can be used especially effectively to regenerate a particle filter partially loaded with soot particles. The inventive type of regeneration can be realized with the use of the existing technical devices already on the engine; that is, there is no need in practice for any additional design measures or apparatus; on the contrary, the only additional step required is increase the “depth” of the open and closed-loop control system to handle the regeneration function with the existing devices. In general, therefore, according to the invention, a particle filter partially loaded with soot particles will never be regenerated except during exhaust braking phases of the engine: it will be started after the exhaust braking phase has been initiated, and it will continue during the rest of the exhaust braking phase. During such an exhaust braking phase, the speed of the diesel engine is decelerated to a lower-to-medium rpm range significantly below the nominal rpm&#39;s, and a certain quantity of diesel fuel is injected via the engine&#39;s own injection valves into the cylinders of the exhaust-braked diesel engine, namely, at a time which is significantly after top dead center (TDC). In addition, technical control measures are taken to ensure that part of the hot gas mixture which then is present in the backpressure area of the blocked-off exhaust gas line and which contains a certain amount of unburned fuel and the air which has become highly compressed during the exhaust braking process can flow through the butterfly valve or bypass it. During the regeneration of the partially soot-loaded particle filter, this hot gas mixture which has passed through or by the butterfly valve acts during the exhaust braking phase as a highly efficient oxidizing agent, which, at the beginning of the regeneration phase, brings about the initial ignition of the soot and then supports its accelerated oxidation/combustion. 
         [0009]    Because every regeneration of the particle filter according to the inventive method leads to the consumption of a certain amount of fuel, it is advisable, before the initiation of a regeneration phase, to question, i.e., to determine, the necessity of a particle filter regeneration. This is done, for example, by detecting the pressure values representative of the degree to which the filter is loaded with soot particles, such as the exhaust gas backpressure in the exhaust gas train. It is also possible to specify in advance a value range for the degree of soot loading and either to set the regeneration process in motion immediately whenever the actual soot load lies within the specified value range, or, depending on the situation, to initiate it after a certain time delay. In this case, a certain nominal range will be predefined for the evaluation of the detected pressure values representative of the soot particle load. By comparing the transmitted actual pressure values with the pressure values of the nominal range, it is then possible, depending on the position of the actual pressure values within this range, to determine whether a regeneration is necessary at once or whether it can instead be started at a later time. In this way, it is possible to avoid the unnecessary consumption of fuel. 
         [0010]    The quantity of fuel needed to regenerate the particle filter can also be limited by adjusting it within a regeneration phase as a function of detected actual temperature values of the particle filter, namely, by adjusting it to comparatively large injection quantities at low particle filter temperatures and to smaller injection quantities at higher particle filter temperatures. The start of a fuel injection or of a fuel injection sequence can, in terms of technical control measures involved, lie within in a range between “minimally after TDC”, e.g., 5 crankshaft degrees after TDC, and “maximally after TDC”, e.g., 120 crankshaft degrees after TDC, and the quantity of fuel to be injected can also be adjusted variably to suit the circumstances. 
         [0011]    To limit the consumption of fuel required for particle filter regeneration even more, it is also effective to determine the actual regeneration state of the particle filter within a regeneration phase. Once again, this can be done by detecting operating values representative of this state such as the exhaust gas backpressure in the exhaust gas train. The regeneration phase is terminated as soon as an operating value representative of a sufficient degree of regeneration has been obtained. 
         [0012]    It is known in the case of certain diesel engines installed in MAN trucks and busses that, to avoid the coking which might occur as a result of the overheating of the injection nozzle heads projecting into the combustion chambers during an exhaust braking phase when the exhaust braking rpm&#39;s are in the range of the nominal rpm&#39;s and the compressed air takes on extremely high temperatures, fuel can be injected into the cylinders for a brief period of time to cool the injection nozzle bores. See the diagram in  FIG. 2 , which illustrates these relationships. In the load-versus-rpm diagram according to  FIG. 2 , DM designates the torque curve of the diesel engine at full load, BK the brake power curve obtained when the diesel engine is operating in exhaust braking mode, and an the fuel injection map for nozzle cooling during exhaust braking mode. As can be seen, the nozzle-cooling injection map an lies in the area of the nominal rpm value nm of the diesel engine. The nominal rpm line is designated nN. When the braking rpm value of the diesel engine is in this heat-critical rpm range, fuel is injected briefly to cool the injection nozzles. The injection of fuel to cool the injection nozzles, however, is not related in any way to the inventive particle filter regeneration method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a torque vs. RPM diagram, showing the fuel injection map, according to the invention; 
           [0014]      FIG. 2  is a torque vs. RPM diagram, showing the fuel injection map, according to the prior art; and 
           [0015]      FIG. 3  is a schematic diagram of a diesel engine for practicing the inventive method. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    In the following, the inventive method is explained in greater detail on the basis of the diagram of  FIG. 1  and a schematic diagram of a diesel engine according to  FIG. 3 . 
         [0017]      FIG. 3  shows a schematic diagram of a diesel engine  1  installed in a vehicle such as a truck, bus, or other utility vehicle. Each of six cylinders  2  has two outlet valves, each of which communicates with an exhaust gas-collecting manifold  4  by way of an outlet channel  3 . In the case shown here, the cylinders  2  are divided into two banks of three each, and each bank is connected to one manifold  4 . Both manifolds  4  lead to the turbine  5  of an exhaust gas turbocharger  6  and are components of the exhaust gas train of the diesel engine  1 , which, on the outlet side of the turbine  5 , is connected to a section  7 , in which a particle filter  8  is installed. In the example shown here, an oxidation catalyst  9  is installed upstream of the particle filter  8 . This catalyst is responsible for producing a significant increase in the quantity of NO x  present in the exhaust gas, whereas the particle filter  8  serves the primary purpose of separating/filtering out and of oxidizing the soot particles present in the exhaust gas. 
         [0018]    A compressor  10  is connected to the turbine  5  of the exhaust gas turbocharger  8 . This compressor compresses the charge air and sends it through a charge air line  11  and the intake channels  12  branching off from it into the cylinders  2 , which receive the charge air in a controlled manner through the intake valves, two per cylinder. 
         [0019]    The diesel engine  1  is equipped with a common rail injection system, the main components of which are a high-pressure delivery pump  13 , a high-pressure distribution rail  14 , and six injection valves  16 , each of which is connected to the rail  14  by a high-pressure connecting line  15 . So that they can be actuated, the injection valves  16  have electromagnetic-electronic control heads, which receive their injection control commands via electrical control lines  17  from a computer-based electronic control unit  18 . This unit  18  includes as its main components a CPU (Central Processing Unit), a data storage unit, and input/output interface devices. 
         [0020]    The diesel engine  1  is also equipped with an internal exhaust pressure braking device, e.g., one like that which is known in professional circles as the MAN-EVB®, over a million of which have already been installed in MAN engines. This exhaust braking device includes a butterfly valve  19 , which can be located in the exhaust gas train of the diesel engine either upstream or downstream of the turbine  5  of the exhaust gas turbocharger  6 . In the example according to  FIG. 3 , the butterfly valve  19  is installed directly upstream of the inlet to the turbine  5 , i.e., between the turbine and the manifold  4 . The valve  19  can be switched between its normal position (=full pass-through) and a blocking position (=exhaust braking mode position) by a servomotor  20 , which preferably also receives control commands from the control unit  18 . The blocking position can be such that the gas in the blocked-off section of the exhaust gas train, i.e., the gas in the area of the manifold  4 , is indeed backed up, but nevertheless a small amount of this backed-up gas is still allowed to pass through. The possibility is also available of using the butterfly valve  19  to block off the exhaust gas train completely and to allow a small amount of the backed-up gas to flow through a bypass line  22 , which can be opened and closed by a valve or butterfly valve  21 . This version is shown in dotted line in  FIG. 3 . The servomotor  21 ′ of the valve or butterfly valve  21  also receives its control commands from the control unit  18 . 
         [0021]    Pressure sensors  23  and  24 , installed upstream and downstream of the particle filter  8 , detect the pressures prevailing in the exhaust gas train  7  at the measurement sites in question and transmit them as actual pressure values to the control unit  18  via measurement lines  25 ,  26 . A temperature sensor  28  detects the temperature in the particle filter  8 , and a temperature sensor  28  detects the temperature in the oxidation catalyst  9 . The actual temperature values thus detected are also transmitted to the control unit  18 , in this case via measurement lines  29 ,  30 . 
         [0022]    In the following, the inventive method for regenerating the particle filter  8  is explained in greater detail on the basis of the diagram of  FIG. 1  in conjunction with a diesel engine  1  of the type illustrated in  FIG. 3  and described above. This method is characterized in that a particle filter  8  partially loaded with separated soot particles is never regenerated except during exhaust braking mode. In the diagram according to  FIG. 1 , M d  stands for the torque, and n M  stands for the rpm&#39;s of the diesel engine  1 . The nominal rpm value of the diesel engine  1  is indicated in the diagram by the line nm. The full-load torque curve is indicated in the diagram by DM. The course of the exhaust braking power which occurs during exhaust braking is indicated in the diagram by the curve BK. A regeneration phase for the particle filter  8  is started when the driver of the vehicle initiates an exhaust braking phase; the control unit  18  receives this control input via the signal line  31  and transmits the commands by means of which the butterfly valve  19  and, if present, the valve or butterfly  21  are moved into their exhaust braking mode positions. The control unit  18  knows the exhaust gas backpressure in the exhaust gas train  7  on the basis of the pressure values which are being transmitted continuously to it by the pressure sensors  23 ,  24  or which it accepts from them at regular intervals. 
         [0023]    This exhaust gas backpressure, which the control unit  18  either already knows prior to an exhaust braking phase or which, alternatively, it knows only after the start of an exhaust braking phase by requesting the pressure values from the pressure sensors  23 ,  24 , is representative of the degree to which the particle filter  8  is loaded with soot particles. Because the inventive regeneration method causes a certain amount of fuel to be consumed, it is advisable to determine the necessity for regenerating the particle filter  8  beforehand, e.g., on the basis of the detected exhaust gas backpressure, and then, as a function of that determination, to initiate the regeneration by means of the additional inventive measures only if necessary. As part of the process for determining the necessity for regeneration, a certain nominal range can be predefined for the evaluation, to be conducted by the control unit  18 , of the detected pressure values representative of the soot particle loading of the particle filter  8 . By comparison of the detected actual pressure values with the pressure values of the nominal range in the control unit  18 , it is determined on the basis of the location of the actual pressure values within the latter whether it is necessary to regenerate the particle filter immediately or whether the regeneration can be started at some later time. As a result, it is possible to limit the amount of fuel which must be consumed for regeneration. 
         [0024]    The regeneration measures themselves are specified by the control unit  18 . If an exhaust braking phase has been initiated and if it has been found that it is necessary to regenerate the particle filter, the particle filter regeneration process is started and then executed within this exhaust braking phase. Via the engine&#39;s own injection valves  16 , a certain quantity of diesel fuel is injected into the cylinders  2  of the exhaust pressure-braked diesel engine at a time which is, in each case, significantly after the top dead center (TDC) point. In addition, the control unit  18  initiates control measures by which some of the hot gas mixture now present in the blocked-off part  4  of the exhaust gas train, consisting of a certain amount of vaporized, unburned fuel and a certain amount of air, which has become highly compressed during the exhaust braking mode, can pass through or bypass the butterfly valve  19 . This hot gas mixture then arrives in the downstream particle filter  8 , in which, acting as a highly efficient oxidizing agent, it produces an initial ignition of the soot deposited there and then supports its accelerated oxidation. 
         [0025]    In the diagram of  FIG. 1 , the area in which the fuel is injected for the regeneration of the particle filter  8  is shown by the injection map c. It size, designated by the boundary line b, is defined by the injection times and injection quantities used during a regeneration phase. From the diagram according to  FIG. 1 , it can be seen from the injection map c that the regeneration of the particle filter  8  during an exhaust braking phase occurs within an rpm range of the decelerated diesel engine  1  which is significantly below the nominal rpm value nm of the diesel engine  1 , i.e., in its lower-to-medium rpm range. Within an activated regeneration phase controlled by the control unit  18  during an exhaust braking phase, the timing of the start of the fuel injection into each cylinder  2  is fixed in a range between minimally after TDC, e.g., approximately 5 crankshaft degrees after TDC, and maximally after TDC, e.g., 120 crankshaft degrees after TDC, and the quantity of fuel to be injected, defined on the basis of the length of the injection time, is fixed as a function of the detected actual temperature value of the particle filter  18 , so that comparatively long injection times with large injection quantities are used at lower particle filter temperatures, whereas shorter injection periods with smaller injection quantities are used at higher particle filter temperatures. It is also possible, however, to divide the injection period into several shorter timed injections. 
         [0026]    During a regeneration phase activated within an exhaust braking phase, it is advisable to determine the actual degree to which the particle filter  8  has been regenerated so as not to cause the consumption of an unnecessary amount of fuel. This is accomplished again by detection of operating values relevant to the purpose, such as the exhaust gas backpressure in the exhaust gas train  7  by means of the pressure sensors  23 ,  24  and their evaluation by the control unit  18 . The control unit  18  takes care of terminating a regeneration phase as soon as it detects an operating value representative of a satisfactory degree of regeneration. 
         [0027]    The invention provides a highly efficient method for the regeneration of particle filters, especially of the type installed in vehicles in which, as a result of their intended uses, a high particle filter temperature sufficient for continuous, independent regeneration is not or only seldom reached. 
         [0028]    The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.