Abstract:
A method for regulating the speed of an internal combustion engine. According to the invention, a second regulation difference (dR 2 ) is calculated by a second filter in the event of dynamic changes of state. In this way, in the event of dynamic changes of state, a speed regulator defines a power-determining signal (ve) according to a first regulation difference (dR 1 ) and the second regulation difference (dR 2 ). The inventive method thus increases the dynamics of the control loop.

Description:
PRIORITY CLAIM 
   This is a 35 U.S.C. §371 National Stage of International Application No. PCT/EP2003/012786, filed on Nov. 15, 2003. Priority is claimed on that application and on the following application: 
   Country: Germany, Application No. 102 53 739.9, Filed: Nov. 19, 2002. 
   BACKGROUND OF THE INVENTION 
   The invention concerns a method for the closed-loop speed control of an internal combustion engine. 
   The speed of a drive unit is typically automatically controlled to an idling speed and a final speed. A drive unit is understood to mean either an internal combustion engine-transmission unit or an internal combustion engine-generator unit. To achieve closed-loop speed control, the speed of the crankshaft is detected as a controlled value and compared with an engine speed set value, i.e., the reference input. The resulting control deviation is converted by a speed controller to a correcting variable for the internal combustion engine, for example, an injection quantity. The problem with a control loop of this type is that torsional oscillations, which are superimposed on the controlled value, can be amplified by the speed controller. This can lead to instability of the closed-loop control system 
   The problem of instability is countered by a speed filter in the feedback path of the closed-loop speed control system. EP 0 059 585 B1 describes a speed filter of this type, in which the timing values of a shaft teeth are detected by means of an operating cycle of the internal combustion engine. The operating cycle is defined as two revolutions of the crankshaft, corresponding to 720°. These tooth timing values are then used to calculate a filtered tooth timing value by taking the arithmetic mean. This filtered tooth timing value corresponds to the filtered actual speed value, which is then used for the automatic control of the internal combustion engine. 
   A closed-loop speed control system for automatically controlling a drive unit with a speed filter of this type in the feedback path is described, for example, in DE 199 53 767 C2. 
   However, the problem with this two-revolution filter in the feedback path is that stable behavior of the drive unit is accompanied by deterioration of the design load behavior. 
   SUMMARY OF THE INVENTION 
   The goal of the invention is to optimize the closed-loop speed control system with respect to design load behavior. 
   In accordance with the invention, a second filter is used to compute a second filtered actual speed from the actual speed of the internal combustion engine, and then a second control deviation is computed from this second filtered actual speed. In the event of a dynamic change of state, the speed controller computes a power-determining signal, for example, an injection quantity, from the first and second control deviations. In this regard, the power-determining signal in the event of a dynamic change of state is substantially determined from the second control deviation. 
   A dynamic change of state occurs when a large deviation between set and actual speed values is present, for example, when a load application or load rejection occurs. The second filter is realized, e.g., as a mean value filter with a filter angle of 90°, for fast detection of this dynamic event. Compared to the two-revolution filter, a filtered speed value is present at a significantly earlier point in time, i.e., the dynamic change of state is detected faster. 
   The invention offers the advantage that couplings with a low natural frequency can be used. Since the second filter constitutes a pure software solution, it can be subsequently integrated in already existing engine control software. 
   When a dynamic change of state occurs, the second control deviation acts on a proportional component (P component) or a DT 1  component of the speed controller. Suitable characteristic curves are provided for this purpose. 
   Preferred embodiments of the invention are illustrated in the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  shows a system diagram; 
       FIG. 2  shows a closed-loop speed control system; 
       FIG. 3  shows a functional block diagram of the speed controller; 
       FIG. 4  shows a characteristic curve; 
       FIG. 5  shows a functional block diagram of the speed controller (second embodiment); and 
       FIG. 6  shows a characteristic curve. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a system diagram of the overall system of a drive unit  1 , for example, an internal combustion engine-generator unit. It comprises an internal combustion engine  2  with an engine load  4 . The internal combustion engine  2  drives the engine load  4  via a shaft with a transmission element  3 . In the illustrated internal combustion engine  2 , the fuel is injected by a common-rail injection system. This injection system comprises the following components: pumps  7  with a suction throttle for conveying the fuel from a fuel tank  6 ; a rail  8  for storing the fuel; and injectors  10  for injecting the fuel from the rail  8  into the combustion chambers of the internal combustion engine  2 . 
   The internal combustion engine  2  is automatically controlled by the electronic control unit (EDC)  5 . The electronic control unit  5  contains the usual components of a microcomputer system, for example, a microprocessor, interface adapters, buffers, and memory components (EEPROM, RAM). The relevant operating characteristics for the operation of the internal combustion engine  2  are applied in the memory components in input-output maps/characteristic curves. The electronic control unit  5  uses these to compute the output variables from the input variables.  FIG. 1  shows the following input variables as examples: a rail pressure pCR, which is measured by means of a rail pressure sensor  9 ; an actual speed nM(IST) of the internal combustion engine  2 ; an input variable E; and a signal FP for the power presetting by the operator. In a motor vehicle application, this corresponds to the position of the accelerator pedal. Examples of input variables E are the charge air pressure of the turbochargers and the temperatures of the coolant/lubricant and the fuel. 
   As output variables of the electronic control unit  5 ,  FIG. 1  shows a signal ADV for controlling the pumps  7  with a suction throttle and an output variable A. The output variable A is representative of the other control signals for automatically controlling the internal combustion engine  2 , for example, the injection start SB and a power-determining signal ve, which corresponds to the injection quantity. 
     FIG. 2  shows a functional block diagram of the closed-loop speed control system. The input variable of the closed-loop speed control system is a set speed nM(SL). The output variable of the closed-loop speed control system is the unfiltered actual speed nM(IST). A first filter  12  for computing the first actual speed nM 1 (IST) from the current unfiltered actual speed nM(IST) is provided in a first feedback path. The first filter  12  is usually designed as a two-revolution filter, i.e., it averages the actual speed NM(IST) over one operating cycle corresponding to 720° of the crankshaft. A second filter  13  for computing a second actual speed nM 2 (IST) from the current unfiltered actual speed nM(IST) is provided in a second feedback path. The second filter  13  is realized, e.g., as a mean value filter with a filter angle of a 90° crankshaft angle. The second filter  13  thus has significantly greater dynamics than the first filter  12 . 
   A first control deviation dR 1  is computed at a first comparison point A. It is determined from the set speed nM(SL) and the first actual speed nM 1 (IST). The first control deviation dR 1  is the input variable of the speed controller  11 . A second control deviation dR 2  is computed at a second comparison point B. It is determined from the set speed nM(SL) and the second actual speed nM 2 (IST). The second control deviation dR 2  is also supplied to the speed controller  11 . The internal structure of the speed controller  11  will be explained in connection with the description of  FIGS. 3 and 5 . The speed controller  11  determines a correcting variable from the input variables. In  FIG. 2 , this correcting variable is designated as a power-determining signal ve. The power-determining signal ve represents the input variable for the controlled system, which in the present case is the internal combustion engine  2 . The output variable of the controlled system corresponds to the unfiltered actual speed nM(IST). The automatic control system is thus closed. 
   The invention is designed in such a way that during steady-state operation of the drive unit, the speed controller  11  computes the power-determining signal ve exclusively as a function of the first control deviation dR 1 . When a dynamic change of state occurs, the speed controller  11  determines the power-determining signal ve as a function of the first control deviation dR 1  and the second control deviation dR 2 . 
     FIG. 3  shows a functional block diagram that represents a first embodiment of the internal structure of the speed controller  11 . The speed controller  11  comprises a proportional component (P component)  15  for determining a proportional component ve(P) of the power-determining signal ve, an integral-action component (I component)  16  for determining an integral-action component ve(I) of the power-determining signal ve, a characteristic curve  14 , and a summation unit  18 . The first control deviation dR 1  is the input variable for the P component  15  and the I component  16 . The second control deviation dR 2  is supplied to the characteristic curve  14 . The output variable of the characteristic curve  14  is a factor kp 2 , which acts on the P component  15 . Another input variable of the P component  15  is a factor kp 1 . The characteristic curve is shown in  FIG. 4 . Values of the second control deviation dR 2  are plotted in the positive/negative direction on the x-axis. The y-axis represents the factor kp 2 . A first limiting value GW 1  and a second limiting value GW 2  are plotted on the x-axis. At very large negative values of the second control deviation dR 2 , the factor kp 2  is limited to a value GW 3 . A negative control deviation is present when the second actual speed nM 2 (IST) is greater than the set speed nM(SL). At positive second control deviations dR 2  that are greater than the second limiting value GW 2 , the factor kp 2  is limited to the value GW 4 . In the region between the first limiting value GW 1  and the second limiting value GW 2 , the factor kp 2  is set to the value zero. It is apparent from the characteristic curve  14  that in the steady state, i.e., where the second control deviation dR 2  is almost zero, the factor kp 2  has a value of zero. Consequently, the P component  15  of the speed controller  11  is determined in this case exclusively from the first control deviation dR 1 . In the event of dynamic changes of state, i.e., where there is a large negative or positive second control deviation dR 2 , the factor kp 2  acts on the P component  15  of the speed controller  11 . The P component of the power-determining signal is now computed as a function of the first control deviation dR 1  and the factors kp 1  and kp 2 :
   ve ( P )= dR 1·( kp 1 +kp 2) 
where
     ve(P)=proportional component of the power-determining signal ve   dR 1 =first control deviation   kp 1 =first factor   kp 2 =second factor   
   The factor kp 1  can either be preset as a constant or computed as a function of the first actual speed nM 1 (IST) and/or the I component ve(I). 
   Another possibility for computing the P component ve(P) is to use the control deviation dR 2  directly for the computation of the P component  15 :
 
 ve ( P )= dR 1 ·kp 1 +dR 2 ·kp 2
 
where
     ve(P)=proportional component of the power-determining signal ve   dR 1 =first control deviation   dR 2 =second control deviation   kp 1 =first factor   kp 2 =second factor   

   This embodiment is shown by the dotted line in  FIG. 3 . The P component and the I component are added in the summation unit  18 . The sum corresponds to the power-determining signal ve. 
     FIG. 5  shows a functional block diagram of a second embodiment of the internal structure of the speed controller  11 . In this embodiment, in contrast to the embodiment shown in  FIG. 3 , the second control deviation dR 2  is supplied to the P component  15  and simultaneously to a DT 1  component  17 . The DT 1  component  17  computes the DT 1  component ve(DT 1 ) of the power-determining signal ve. The summation unit  18  then computes the power-determining signal ve from the addends of the P component, I component, and DT 1  component. The DT 1  component  17  is computed by a characteristic curve  19 , which is shown in  FIG. 6 . The time t is plotted on the x-axis. The y-axis corresponds to the DT 1  component ve(DT 1 ) of the power-determining signal ve. When there is a sudden change in the second control deviation dR 2 , it is assigned a corresponding value ve(DT 1 ) by the characteristic curve  19 . Two limiting values GW 1  and GW 2  are plotted on the graph. The DT 1  component is deactivated if the second control deviation dR 2  becomes smaller than the first limiting value GW 1 , i.e., the signal ve(DT 1 ) then has a value of zero. The DT 1  component is activated if the second control deviation dR 2  becomes greater than the second limiting value GW 2 . The effect of the limiting value GW 2  is that, when there are dynamic changes of state, i.e., when the second control deviation dR 2  has large positive or negative values, the DT 1  component is also incorporated in the computation of the power-determining signal ve. When a steady state exists, i.e., where the second control deviation dR 2  is practically zero, the power-determining signal ve is determined exclusively from the P component and the I component. 
   Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.