Patent Publication Number: US-6665607-B2

Title: Method and device for controlling an internal combustion engine

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and a device for controlling an internal combustion engine. 
     BACKGROUND INFORMATION 
     Such a method and such a device for controlling an internal combustion engine are known from the German Published Patent Application No. 195 27 218. There, a method and a device are described for controlling the smooth running of an internal combustion engine. A manipulated variable can be preset on the basis of at least one measured quantity, which here is the speed of the internal combustion engine. To form the manipulated variable, the measured quantity is filtered by at least one filter means. Usually in the case of a smooth-running control, each cylinder of the internal combustion engine is assigned a control which, as a function of a system deviation allocated to it, forms a manipulated variable for the cylinder assigned to it. The system deviation is derived from the actual values and setpoint values allocated to the individual cylinders. The time intervals between two combustions or the duration of at least one segment, which is defined by a segmental wheel, are used as the actual value. The setpoint values are preferably yielded by an averaging using all actual values. 
     The spacing between two pulses on a so-called segmental wheel is usually designated as a segment. In this context, the interval between two combustions is generally divided into two segments. The segmental wheel can be placed on the camshaft or the crankshaft and delivers two pulses per combustion process. Alternatively, the segment pulses can also be generated on the basis of other signals. 
     The actual and setpoint values are preferably ascertained in a frequency-specific manner, i.e. the output signal of the speed sensor is filtered by band-pass filters, and the actual and setpoint values for a frequency are formed on the basis of this filtered signal. Provision is made to weight the amplification of the band-passes and/or the frequency-specific system deviation. These weighting factors are usually stipulated within the framework of the application. It is also provided that, to form the frequency-specific actual values for different frequencies and different vehicle types, different segments are selected which take into account the frequency-specific and vehicle-specific phase shifts between quantity oscillation and rotational-speed oscillation. Therefore, it is likewise established within the framework of the application, which segments are utilized for actual value formation and/or setpoint value formation. 
     Due to this stipulation of the segment selection and of the band-pass amplification, a considerable outlay results in the application. 
     SUMMARY OF THE INVENTION 
     Using the procedure of the present invention, the outlay can be markedly reduced in the application. In particular, the time expenditure and the requirement for measuring technology can be reduced, since no external measuring instruments are necessary. 
     Because an excitation variable is superimposed on the manipulated variable, and because properties of the filter means are determined on the basis of the resulting reaction of the measured quantity, the properties of the filter means can be adapted individually to the respective vehicle. 
     According to the present invention, the properties of the filter means are determined in preferred operating states. The determination is preferentially carried out at the end of the vehicle manufacture and/or within the framework of servicing the vehicle. Thus, the properties can be optimally selected over the entire service life of the vehicle. 
     It is particularly advantageous if the filter means are constructed as a band-pass filter with adjustable amplification. In this case, the band-pass amplification is adapted. 
     If the filter means ascertains an actual value and/or a setpoint value by evaluating specific rotational-speed segments, then this segment selection is designated as a property of the filter means. 
     The amplification and the segment selection determine the properties of a smooth-running control. The performance of the vehicle can be favorably influenced by a precise adaptation of these variables to the respective vehicle. 
     It is particularly advantageous if a periodic variable is used as excitation variable whose frequency corresponds to the crankshaft frequency, the camshaft frequency and/or an integral multiple of these frequencies. These frequencies correspond to the disturbances generally occurring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a block diagram of the device according to the present invention. 
     FIG. 2 shows a detailed representation as a block diagram of the actual-value determination. 
     FIG. 3 shows a flow chart for the purpose of illustrating the procedure according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     In the following, the procedure of the present invention is presented using a smooth-running control as an example. However, the procedure according to the present invention is not limited to this exemplary embodiment; it can also be used for other open-loop and/or closed-loop controls for internal combustion engines. It can be used in particular when a manipulated variable is specifiable starting from at least one measured quantity. If this manipulated variable acts upon the internal combustion engine, this results in a corresponding change in the measured quantity. 
     FIG. 1, in a rough schematic fashion, shows a smooth-running control for an internal combustion engine as a block diagram. The internal combustion engine is designated by  100 . A fuel-quantity-demand input  110  sends a fuel-quantity demand MW via a node  115  to a volume-flow controlling unit (not shown) of internal combustion engine  100 . Speed N of the internal combustion engine is detected by a sensor  125 . A corresponding signal arrives at a smooth-running control  130 . The speed signal is evaluated by filtering  140  which then in turn applies a corresponding signal to a manipulated-variable determination element  145 . Manipulated-variable determination element  145  determines a correction quantity K which is combined in node  115  with fuel-quantity demand MW. 
     Usually a fuel-quantity demand MW is determined by fuel-quantity-demand input  110  starting from the driver command which, for example, is acquired with an accelerator pedal. This variable or a variable corresponding to this variable is supplied to the volume-flow controlling unit of internal combustion engine  100 , this volume-flow controlling unit then establishing the fuel quantity to be injected corresponding to this signal. Solenoid valves, piezoelectric actuators or other actuators are generally used as volume-flow controlling unit, which establish the start of injection, the end of injection and thus also the injection quantity as a function of their trigger signal. 
     It is usually desired that all cylinders of an internal combustion engine contribute the same torque to the total torque. Because of tolerances, the individual cylinders contribute differently to the total torque in response to the same trigger signal. To compensate for this, a smooth-running control is provided which, on the basis of the speed signal, provides a suitable correction value K that is determined such that all cylinders contribute the same torque to the total torque. 
     To this end, as presented in the related art, a cylinder-specific actual value and setpoint value are calculated on the basis of the speed value, and the actual value is adjusted to the setpoint value. A suitable filtering  140  is shown in detail in FIG.  2 . 
     The filter means preferably includes at least one band-pass with adjustable amplification. Furthermore, filter means  140  determines at least one actual value and/or at least one setpoint value by evaluating specific segments of a speed signal. The properties of the filter means are determined by the amplification of the band-pass and the segments which are utilized for forming the actual values and/or setpoint values. 
     FIG. 2 shows actual-value determination  140  in detail. Elements already described in FIG. 1 are marked with corresponding reference numerals in FIG.  2 . The output signal of sensor  125  is supplied to a first filter  210  and a second filter  220 . The output signal of first filter  210  arrives, via a node  215 , at a first setpoint-value determination element  212  and a first actual-value determination element  214 . The output signal of second filter  220  arrives, via a node  225 , at a second setpoint-value determination  222  and a second actual-value determination  224 . 
     An amplification-factor input  230  applies a specifiable amplification factor to each node  215  and  225 . The output variables of band-passes  210  and  220  are multiplicatively combined with this amplification factor. In this manner, it is possible to implement band-passes with adjustable amplification. 
     Output signal NWS of first setpoint-value determination  212  arrives with a positive algebraic sign, and output signal NWI of first actual-value determination  214  arrives with a negative algebraic sign, at a node  216 . First system deviation NWL arrives at a summing point  240 , and from there at block  145 . 
     Output signal KWS of second setpoint-value determination  222  arrives with a positive algebraic sign, and output signal KWI of second actual-value determination  224  arrives with a negative algebraic sign, at a node  226 . Second system deviation KWL arrives at summing point  240 . 
     Available at the output of summing point  240  is system deviation L which is routed to manipulated-variable determination  145  that contains the actual smooth-running regulator. 
     In the specific embodiment shown of an internal combustion engine having four cylinders, filters  210  and  220  are band-pass filters whose mid-frequency in the case of filter  210  lies at the camshaft frequency, and in the case of filter  220  lies at the crankshaft frequency. In refinements of the present invention, still further filters can be provided having integral multiples of the crankshaft frequency and/or the camshaft frequency. 
     In particular in the case of an internal combustion engine having 2*1 cylinders, 1 being a natural number, 1 band-passes can be provided whose mid-frequencies lie at an integral multiple of the camshaft frequency. 
     The speed signal is divided into spectral components by band-passes  210  and  220 . The first, second and third actual-value calculators and the first, second and third setpoint-value calculators ascertain frequency-specific setpoint and actual values for each spectral component. The setpoint and actual values are preferably calculated differently for the individual spectral components. 
     The speed signal is divided for the individual frequencies by band-passes  210  and  220 . First actual-value input  214  and second actual-value input  224  calculate a frequency-specific actual value for each frequency. Correspondingly, it can be provided that first setpoint-value input  212  and second setpoint-value determination  220  calculate a frequency-specific setpoint value for each frequency. 
     Alternatively to the adjustable amplification of band-passes  210  and  220 , provision can also be made for the frequency-specific system deviations to be weightable by weighting factors. The weighting factors and/or the amplification of the band-passes is/are selected such that the closed-control-loop amplification is identical for all frequencies. 
     The segment selection is preferably carried out in a frequency-specific manner. This means different segments are utilized for calculating the actual values and/or the setpoint values for the individual frequencies. The frequency-specific system deviation is then ascertained in nodes  216  and  226 . Furthermore, the segment selection can be preset nearly arbitrarily. 
     In the related art, the properties of the filter means are ascertained within the framework of the application and stored in the control unit. These application quantities are no longer corrected. As a result, the smooth-running control no longer operates optimally due to the effects of ageing. 
     Therefore, according to the present invention, the properties of the filter means, which in the following are also designated as control parameters, are adapted. This holds true in particular for the amplification of the band-passes and for the segment selection. To that end, the procedure of the present invention is as follows. 
     The allocation of a rotational-speed reaction to the causative cylinder is crucial for the functioning of the smooth-running control. Namely, this cylinder should receive more or less fuel quantity accordingly. The allocation can be determined from the frequency response characteristic. The phase shift between fuel quantity and speed is decisive for the frequency response characteristic. The segments into which the reaction falls are calculated on the basis of the phase shift. These segments are evaluated for forming the actual values. Actual-value determinations  214  and  224  and/or setpoint-value determinations  212  and  222  evaluate the segments thus ascertained for forming the actual values and/or setpoint values. That is to say, the segment selection is calculated as a function of the phase shift of the controlled system. 
     For each frequency considered, one or more segments result into which the reaction following the injection falls. The segments are usually different for each frequency. 
     In certain operating states in which such an adaptation is possible, an excitation variable is superimposed on the manipulated variable that is applied to the fuel-quantity positioner. Preferably a periodic signal is superimposed on the fuel-quantity signal. This quantity excitation produces rotational-speed oscillations which have a similar effect as the tolerances of the system, i.e. rotational-speed oscillations occur. The response of internal combustion engine  100  can be determined on the basis of the quantity excitation and the resulting rotational-speed oscillations. The response of the internal combustion engine is defined by the phase shift and the controlled system gain. 
     Starting from the phase shift thus ascertained and the controlled system gain or the amplitude response, the control parameters are then calculated. They are basically the amplification of the band-passes and the segment selection. 
     FIG. 3 shows a suitable procedure as a flow chart. In a first step  300 , it is checked whether an operating state exists in which the adaptation can be carried out. It is particularly advantageous if the adaptation is triggered by external influences. Thus, the adaptation can preferably be carried out after the installation of the internal combustion engine during its first operation. It is also advantageous if the adaptation is carried out at regular intervals when the internal combustion engine, that is to say, the vehicle is serviced. 
     The normal operation of the internal combustion engine is not impeded during an adaptation at the end of the assembly line or within the framework of servicing. It is also possible to carry out the adaptation in certain stationary operating states such as in idle running. 
     If such an operating state is achieved, then in step  310 , the quantity excitation is carried out, i.e. an additional signal is superimposed on fuel-quantity demand MW. By preference, this additional signal, also designated as excitation variable, is a periodic signal whose frequency preferably corresponds to the crankshaft frequency, the camshaft frequency and/or an integral multiple of these frequencies. 
     Subsequent query  320  checks whether a waiting time has elapsed since the quantity excitation in step  310 . If this is not the case, the excitation variable continues to be superimposed on the fuel-quantity demand If the waiting time has elapsed, then the resulting rotational-speed oscillations are detected in step  330 . In subsequent step  340 , a counter Z is increased. Query  350  checks whether counter Z is greater than a value K. Value K corresponds to the number of the various quantity excitations. 
     If query  350  detects that number Z is greater than value K, i.e. various quantity excitations were implemented and the corresponding rotational-speed oscillations were detected, then in step  360 , the response of the engine, which is determined in particular by the amplification, the amplitude response and the phase shift by the engine, is ascertained. The control parameters are ascertained in step  370  on the basis of these quantities. 
     This means that various quantity excitations are generated in succession and the corresponding engine speed is analyzed in order to determine the control parameters of the smooth-running control. In this context, the analysis phase is subdivided into a transient phenomenon, which is defined by the waiting time in step  320 , in which the internal combustion engine and the operating parameters achieve stationary states again. The engine-speed amplitudes are subsequently measured. The controlled system gain and the phase shift, which are caused by the internal combustion engine, are calculated on the basis of the quantity excitation and the speed amplitude. 
     On the basis of these values for the controlled system gain and the phase shift, which can vary from internal combustion engine to internal combustion engine, smooth-running control  130  calculates the control parameters for the smooth-running control such as, in particular, the segment selection and the amplification of band-pass filters  210  and  220 . 
     According to the present invention, the control unit independently ascertains the control parameters for the smooth-running control. 
     It is particularly advantageous that standard quantities can be used for the control parameters within the framework of the usual application, the standard quantities then being overwritten during the first operation of the internal combustion engine with values ascertained according to the present invention. Within the course of operation of the internal combustion engine, e.g. within the framework of servicing, ageing effects can be compensated by a new application. This means that application expenditure is sharply reduced, the accuracy of the data being markedly improved at the same time. In particular, ageing effects and deviations between internal combustion engines of the same type can be perceptibly reduced.