Abstract:
The invention describes a method and an arrangement for the regulation of the rail pressure in an internal combustion engine. In the method, the rail pressure is regulated, with a target high pressure being predefined. Said target high pressure is filtered, before being input, by way of a target high pressure filter which is configured as a dynamic target high pressure filter.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of PCT application No. PCT/EP2013/002828, entitled “METHOD FOR RAIL PRESSURE REGULATION IN AN INTERNAL COMBUSTION ENGINE”, filed Sep. 19, 2013, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a method and arrangement for the regulation of the rail pressure in an internal combustion engine, wherein the rail pressure is regulated by way of a control unit. 
         [0004]    2. Description of the Related Art 
         [0005]    Various fuel injection systems are commonly used in internal combustion engines. Common rail fuel injection describes a fuel injection system wherein a high pressure pump brings fuel to a high pressure level. The fuel comes into a pipe system, known as the rail, where it is under pressure. The common rail system allows separation of the pressure generation from the actual injection process. The rail pressure is regulated by a pressure control valve or a suction throttle and is monitored by a rail pressure sensor. An automatic control is provided for this, wherein the target rail pressure is preset. 
         [0006]    The internal combustion engine can basically be in a steady state operational state or a transient operational state. In the steady state operational state the rotational speed, as well as the rail pressure are already stable. In the transient operational state this is not the case. In order to reduce fluctuations of the target high pressure in the steady state operational state, a target high pressure filter having a long dwell time is required. In contrast, in the transient operation a target high pressure filter having a very short dwell time is required. In the prior art, a PT1-filter with a constant time constant was used. In order to enable a good steady state performance of the high pressure control circuit this time constant must be set very high. This had the disadvantage that the target high pressure is delayed too much during transient operations. 
       SUMMARY OF THE INVENTION 
       [0007]    One embodiment of the method according to the invention serves to regulate rail pressure in an internal combustion engine, wherein the rail pressure is regulated by way of a controller, whereby a target high pressure is preset which is filtered by way of a target high pressure filter prior to input into the control system. A dynamic target high pressure filter is used as the target high pressure filter whose filter parameter is varied, depending on the operational state of the internal combustion engine. Regulation occurs via a pressure regulator, a controller and a pressure sensor on the rail. 
         [0008]    In one embodiment a time constant of the filter and in another embodiment a filter angle is varied as a filter parameter. In one embodiment a suction throttle is used as pressure regulator. A pressure regulating valve can be utilized alternatively or additionally on the rail. Steady state and transient operating conditions can be considered for the internal combustion engine. In the steady state operation the filter parameter, the time constant, or the filter angle are typically selected to a large value. In the transient operation the filter parameter, the time constant, or the filter angle are typically selected to a small value. 
         [0009]    In one embodiment the transient air mass ratio is the decisive value for the differentiation of steady state and transient operation. The filter parameter may also be calculated over a curve from the transient air mass ratio. Moreover an arrangement to regulate rail pressure in an internal combustion engine that is suitable in particular for implementation of the previously discussed method is provided. This arrangement, which represents a high pressure control circuit includes a controller into which a target high pressure is input, and a target high pressure filter with which the target high pressure is filtered prior to input into the controller, wherein the target high pressure filter is designed dynamically, and whose filter parameter is variable in dependency on the operational condition of the internal combustion engine. A PT1-filter or a mean value filter can be used as dynamic target high pressure filter. 
         [0010]    This method provides good filter performance in steady state operation with a large time constant or respectively large filter angle, and at the same time low filtration in transient operation with a small time constant or respectively small filter angle. This makes possible steep gradients in the target high pressure performance characteristics graph. In transient operation, emissions are reduced and the acceleration process improved. A calculation of the filter parameter, the time constant and/or the filter angle occurs hereby, in dependency on the transient air mass ratio. A PT1-filter is a transmission element which has a proportional transmission behavior with a delay of the first order. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  illustrates a high pressure control circuit according to the current state of the art; 
           [0013]      FIG. 2  illustrates one embodiment of the present invention; 
           [0014]      FIG. 3  illustrates an additional high pressure control circuit according to the current state of the art; 
           [0015]      FIG. 4  illustrates another embodiment of the present invention; 
           [0016]      FIG. 5  illustrates the calculation of an air mass ratio; 
           [0017]      FIG. 6  illustrates the calculation of a dynamic time constant; 
           [0018]      FIG. 7  illustrates the calculation of a dynamic filter angle; 
           [0019]      FIG. 8  illustrates the calculation of a target high pressure; and 
           [0020]      FIG. 9  illustrates time diagrams. 
       
    
    
       [0021]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIG. 1  illustrates a high pressure control circuit  10  of a common rail system according to the current state of the art. Target high pressure P soll   KF  is first determined from a three-dimensional performance characteristics graph  12  with input values of target torque M soll  and engine speed n ist . This is filtered by a PT1 filter  14  with the pre-definable time constant T stat . The actual high pressure P ist  is deducted from the target high pressure. The result is the high pressure control deviation e p  which represents the input value for the high pressure regulator. 
         [0023]    The drawing also shows a controller  16 , a computation unit  18  for a disturbance variable whose output represents a volume flow, a unit  20  for limitation which outputs a manipulated variable, a performance characteristics graph  22  that represents a pump characteristic curve, flow regulator  24 , a computation unit  26  for a PWM-signal, a flow filter  28 , a suction throttle  30 , whereby flow regulator  24 , computation unit  26 , suction throttle  30 , and flow filter  28  form a flow control circuit  32 , a rail pressure pump  34 , a rail  36 , and a pressure filter  38 . 
         [0024]    Note that contradictory criteria applies to the design of time constant T stat : 
         [0025]    The three-dimensional target high pressure performance characteristics graph  12  is determined by the engine test department. An attempt is made to be as flexible as possible, in order to implement random gradients. Very steep performance characteristics graph gradients can, however, lead to instabilities in steady state operation which is prevented by a large time constant T stat  of the target high pressure filter. However, in dynamic processes, a large time constant T stat  of the target high pressure filter leads to an undesirable delay of the target high pressure. The consequences could be higher emission values and a poorer load assumption behavior of the engine. 
         [0026]    The present inventors recognized that a filter needs to be developed that would display a very strong delay behavior in steady state operation, and a low or no delay behavior in transient operation. In this way, it is possible to design the target high pressure performance characteristics graph almost randomly without having to accept disadvantages in transient operation. In addition, emissions can be reduced with such a filter since the target high pressure in the transient operation has a better transition behavior or, in other words, a shorter reaction time. 
         [0027]      FIG. 2  illustrates one embodiment of the invention which is identified with reference number  50 . This arrangement  50  represents a high pressure control circuit with PT1 filter with a dynamic time constant. The illustration shows performance characteristics graph  52 , a PT1-filter  54 , a controller  56 , a computation unit  58  for a disturbance variable whose output represents a volume flow, a unit  60  for limitation which outputs a manipulated variable, a performance characteristics graph  62  that represents a pump characteristic curve, a flow regulator  64 , a computation unit  66  for a PWM signal, a flow filter  68 , a suction throttle  70 , whereby flow regulator  64 , computation unit  66 , suction throttle  70  and flow filter  68  form a flow control circuit  72 , a rail pressure pump  74 , a rail  76  and a pressure filter  78 . The time constant of target high pressure filter  14  is no longer input constantly, but is instead calculated through a two-dimensional curve  80 , depending on the transient air mass ratio. 
         [0028]      FIG. 3  illustrates a high pressure control circuit  100  with a mean value filter having a constant filter angle according to the current state of the art. The illustration shows a performance characteristics graph  102 , a mean value filter  104 , a controller  106 , a computation unit  108  for a disturbance variable whose output represents a volume flow, a unit  110  for limitation which outputs a manipulated variable, a performance characteristics graph  112  that represents a pump characteristic curve, a flow regulator  114 , a computation unit  116  for a PWM signal, a flow filter  118 , a suction throttle  120 , whereby flow regulator  114 , computation unit  116 , suction throttle  120  and flow filter  118  form a flow control circuit  122 , a rail pressure pump  124 , a rail  126 , and a pressure filter  128 . 
         [0029]      FIG. 4  is an additional embodiment of the present invention  150 , namely a high pressure control circuit having a dynamic filter angle. The illustration shows a performance characteristics graph  152 , a mean value filter  154 , a controller  156 , a computation unit  158  for a disturbance variable whose output represents a volume flow, a unit  160  for limitation which outputs a manipulated variable, a performance characteristics graph  162  that represents a pump characteristic curve, a flow regulator  164 , a computation unit  166  for a PWM signal, a flow filter  168 , a suction throttle  170 , whereby flow regulator  164 , computation unit  166 , suction throttle  170  and flow filter  168  form a flow control circuit  172 , a rail pressure pump  174 , a rail  176 , and a pressure filter  178 . The filter angle of mean value filter  154  is no longer input constantly, but is instead calculated through a two-dimensional curve  180 , depending on the transient air mass ratio. 
         [0030]    The calculation of the transient air mass ratio is illustrated in  FIG. 5 : The actual air mass  208  m L  is calculated in a computation unit  206  from charging air pressure  200  p 5 , charging air temperature  202  T 5 , and cylinder volume  204  V H . From a 3D-performance characteristics graph, standard air mass  218  m LN  is calculated from engine target torque  210  Tq and engine speed  212  nist, depending on load shifting condition  214 . Actual air mass  208  is now divided by standard air mass  218 , resulting in dimensionless actual air mass ratios  220 . This is filtered with the assistance of a PT1 filter  222 . The output variable of this filter is the filtered air mass ratio  224 . Transient air mass ratio  226  is resultant from the difference of actual air mass ratio  220  and filtered air mass ratio  224 . 
         [0031]      FIG. 6  shows an example of a two-dimensional curve  250  (dynamic time constant) over which the dynamic time constant T dyn  of target high pressure filter is calculated. The curve is herein divided into three ranges: a steady state range  252  and two dynamic ranges  254  and  256 . Steady state range  252  of curve  250  represents the steady state operating range of the engine. The transient air mass ratio assumes values herein of for example between −0.05 and 0.05. In the steady state operating range of the engine, the time constant of the filter is to assume large values, for example 2 seconds, which causes effective filtering of the target high pressure. 
         [0032]    In the case of a transient process, for example when load shifting, the transient air mass ratio assumes larger values. In the case of a load increase these are negative, and in the case of a load decrease these are positive. For an increasing air mass ratio, a decreasing dynamic time constant T dyn  is defined, so that two negative slopes of a curve result. If the transient air mass ratio exceeds the amount, for example value 0.6, then T dyn  is held for 0.02 seconds constantly on the very small value. 
         [0033]    In an additional embodiment of the target high pressure filter a mean value filter can for example also be utilized in addition to the PT1 filter. Averaging of the target high pressure can herein occur over an angle for example 720° crankshaft or a constant time for example 0.5 seconds. 
         [0034]    A high pressure control circuit  100  with a mean value filter  104  is illustrated as the target high pressure filter in  FIG. 3 . The target high pressure is hereby averaged through the pre-settable filter angle Φ stat .  FIG. 4  also shows a mean value filter  154  where the filter angle is determined over a two-dimensional curve  180  dependent on the transient air mass ratio. This curve  280  is shown in more detail in  FIG. 7 . A stationary operating range  282  is again limited by the two values −0.05 and 0.05 of the air mass ratio. The filter angle in this region is 720° crank angle. Dynamic or respectively transient ranges  284  and  286  are defined by values of the transient air mass ratio which are greater than 0.05. With an increasing air mass ratio the filter angle decreases, resulting in that the filter efficiency becomes less and less. If the air mass ratio ultimately reaches a value 0.6, then the filter angle is equal to 0° crank angle, thereby deactivating the filter. The curves illustrated in  FIGS. 6 and 7  can obviously be applied. 
         [0035]      FIG. 8  shows a flow diagram for calculating the target high pressure. Engine speed nist is calculated in step S 1 . Target torque M soll  is calculated in step S 2 . This target torque is the sum of speed regulator output value and frictional torque. Standard air mass m LN  is calculated in step S 3 . This is the output value of a three-dimensional performance characteristics graph with input values of engine speed n ist  and target torque M soll . In step S 4  the actual air mass (charge air mass) mL is calculated, depending on the charge air pressure, the charge air temperature, and the cylinder volume. In step S 5  the air mass ratio is calculated from the actual air mass and the standard air mass. In step S 6  the air mass ratio is filtered through a PT1-filter. In step S 7  the transient air mass ratio is calculated from the filtered air mass ratio and the actual air mass ratio. From the transient air mass ratio the dynamic filter time constant T dyn  is calculated in step S 8  from a 2-dimensional characteristic curve. From the engine target speed and the target torque the unfiltered target high pressure p soll   KF  is calculated in step S 9  with the assistance of a three-dimensional performance characteristics graph (high pressure demand map). The filtered target high pressure p soll   dyn  is calculated in step S 10  with the assistance of the target high pressure filter (high pressure demand filter). The target high pressure filter uses hereby the dynamic filter time constant T dyn . This concludes the program flow chart. 
         [0036]      FIG. 9  represents the time diagrams of a load increase process of a generator motor. The first diagram  300  shows the motor speed n ist . At point in time t 1  the load is increased, leading to a decline of the motor speed n ist . At a point in time t 5  the motor speed has again built up to the target speed (1500 1/min.) Second diagram  302  shows the target torque (M soll ) of the motor. With the decline of the motor speed, the torque regulator increases the target torque, so that this increases as of point in time t 1 . At point in time t 5  the target torque is also built up. The third diagram  304  shows the transient air mass ratio. In steady state operation, or in other words before point in time t 1 , the transient air mass ratio has a zero value. By increasing the load to time point t 1  the actual air mass ratio decreases whereas the filtered air mass ratio only changes minimally at this time. This results in that the transient air mass ratio becomes negative. At time points t 2  and t 6  the transient air mass ratio assumes the value of −0.05, at time points t 3  and t 4  the value −0.6. At time point t 2  the transient air mass ratio has again built up to the stationary zero value. 
         [0037]    The fourth diagram  306  shows time constant T dyn  of the high pressure filter which was calculated from the transient air mass ratio according to  FIG. 6 . In steady state operation that is up to time point t 1 , the time constant assumes the value of 2.0 seconds. After time point t 2 , the time constant becomes smaller, since the transient air mass ratio falls below value −0.05 at this point in time. From time point t 3  to time point t 4  the transient air mass ratio is smaller than or equal to the value of −0.6. The time constant of the high pressure filter therefore assumes the value of 0.02 seconds in this time range according to  FIG. 6 . At time point t 6  the transient air mass ratio exceeds again the value of −0.05 and subsequently levels off at zero value. This results in that the time constant of the high pressure filter according to  FIG. 6  increases from value 0.02 to value 2.0 seconds from time point t 4  to time point t 6 , and as a result is identical with this value. 
         [0038]    The fifth diagram  308  shows the target high pressure before p soll   KF  and after p soll   dyn  the high pressure filter for the case in which a dynamic time constant according to  FIG. 6  is used for the high pressure filter. A progression of the target high pressure p soll   stat  is indicated for comparison with the broken line, in case that a constant time constant of 2.0 seconds is used. In steady state operation the target high pressure always has a value of 1200 bar before time point t 1 . By increasing the load and simultaneous decline of the engine speed the target high pressure respectively begins to increase. Before the high pressure filter p soll   KF  the target high pressure reaches its steady state end value of 1800 bar at time point t 5 , since at this time point the engine speed n ist  and the target torque M soll  are built up to their steady state final values. 
         [0039]    The target high pressure after the filter reaches the steady state final value at time point t 7  if the dynamic time constant T dyn  is used, which is illustrated by the dotted line p soll   dyn . If a constant time constant of 2.0 seconds is used, then the target high pressure reaches its steady state final value only at time point t 9 . One recognizes that a dynamic filter time constant facilitates a better transitional performance of the target high pressure than a static or respectively constant filter time constant, without having to accept a deterioration of the steady state filter performance. 
         [0040]    The described method offers, at least in some of the embodiments, several advantages: A better transitional performance of the target high pressure is achieved in transient operation. This allows for emissions to be reduced in transient engine operation. Moreover, a better acceleration performance of the engine is achieved with increasing target high pressure, since the target high pressure in this case increases faster and a higher high pressure is advantageous for the dynamic performance. Moreover, this provides more freedom in designing the high pressure performance characteristics graph (high pressure demand map) since steep gradients in the performance characteristics graph do not lead to instabilities. In steady state operation a filter having very good filter efficiency can be used, without thereby compromising the transient operation. 
         [0041]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.