Abstract:
In a method for controlling an actuating device of a valve element of an intake system and/or an exhaust gas system of the internal combustion using an actuating variable, a periodic compensation signal is applied, at least intermittently, to the actuating device. The compensation signal generates a periodic counterforce at the valve element which is directed in the opposite direction from the periodic force exerted by the undesired disturbing vibrations of the valve element.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method and a system for controlling an operation of an actuating device of a valve element of an intake system and/or an exhaust gas system of an internal combustion engine.  
       BACKGROUND INFORMATION  
       [0002]     In modern internal combustion engines, the air flow in the intake system and/or the exhaust gas flow in the exhaust gas system are controlled or regulated by electronically controlled valve devices. The appropriate valve devices are, for example, a throttle valve, and exhaust gas recirculation valve, a bypass valve of a supercharger, etc. Such valve devices normally include a channel through which the air stream and the exhaust gas stream flow, a rotatable or displaceable valve element which controls the flow quantity as a function of its setting, an electrical actuating device, for instance a DC motor, a mechanical connection between the valve element and the actuating device, a sensor that records the current setting of the valve element, and a control and regulation device that ascertains the actuating signal that is applied to the actuating device in order to obtain a desired position of the valve element.  
         [0003]     The known control and regulation devices typically include a digitized, closed control loop by which the actuating signal is determined that is applied to the actuating device. The basis for this is the actual value of the setting of the valve element recorded by the sensor and a setpoint value.  
         [0004]     An object of the present invention is to provide a control method so that the internal combustion engine operates at as high an efficiency as possible, so that the fuel usage is optimized and the emission of pollutants is reduced.  
       SUMMARY OF THE INVENTION  
       [0005]     In usual internal combustion engines, in normal operation, the flow in the intake channel as well as in the exhaust gas channel are subjected to periodic pressure fluctuations that are brought about by the discontinuous flow to and from the combustion chambers based on the opening and closing intake and exhaust valves. These pressure fluctuations generate periodic disturbing forces at a valve element of a valve device situated in such a channel, which lead to undesired vibrations (“disturbing vibrations”) of this valve element, which, in turn, reduce the efficiency in the flow channel.  
         [0006]     The method according to the present invention compensates for such disturbing vibrations of the valve element of a valve device situated in a flow channel, in that a compensation signal is generated which generates a periodic counterforce at the valve element which is directed in the opposite direction from the periodic force exerted by the air flow on the valve element. The disturbing vibrations of the valve element are reduced in this manner or are even completely eliminated, so that the air flow or the exhaust gas flow are able to flow past the valve element at a higher efficiency. Finally, the fuel consumption of the internal combustion engine is reduced thereby, and its exhaust emission behavior is improved. In the process, the advantages according to the present invention are achieved without the dynamics of the valve device being made worse, for example, by mechanical damping elements. Lastly, the advantages according to the present invention are able to be implemented solely by a software design approach, by which an additional compensation signal is generated which is, for example, added to the actual actuating variable and which acts in the counterphase and at the same frequency and the same amplitude of the observed “disturbing vibrations.” 
         [0007]     It is particularly advantageous if the method according to the present invention is subdivided into an initialization portion and a compensation portion. During the initialization portion, the actual compensation of the undesired vibrations is prepared by ascertaining starting variables and/or fixed variables that are used in the generation of the compensation signal. The actual compensation signal is generated only during the compensation portion, and it is based, at least at the beginning, on the starting values ascertained during the initialization portion. As starting values, advantageously, first of all an amplitude and a phase of the current vibrations of the valve element are ascertained.  
         [0008]     During the compensation portion, the properties of disturbing vibrations of the valve element, that are still present, continue to be currently recorded or ascertained, and are used to generate and/or optimize the compensation signal. In this context, the compensation signal is generally characterized by three essential parameters: amplitude, frequency and phase difference from the disturbing vibrations.  
         [0009]     The amplitude of the compensation signal is advantageously ascertained while taking into consideration the starting amplitude ascertained during the initialization portion as fixed value, and a frequency of the current vibrations of the valve element. This is possible to do using little computation effort, and leads to a stable and surprisingly efficient optimization. In practice, a look-up table may be constructed for this purpose, using frequency analysis, from values previously recorded, for instance, on a test stand, which gives the appropriate amplitude of the compensation signal with the aid of the frequency used of the disturbing vibrations and the fixed starting amplitude.  
         [0010]     The frequency of the compensation signal is optimally equal to the frequency of the disturbing vibrations, and the frequency, in turn, can in many cases be derived very simply from the current rotary speed of the internal combustion engine, namely, in all those cases in which the disturbing vibrations are related to the rotary speed-dependent, discontinuous charging and discharging of the combustion chambers.  
         [0011]     The phase difference between the compensation signal and the disturbing vibrations of the valve elements corresponds to a starting value. The latter is ascertained in a similar way as the amplitude, as a function of the frequency of the disturbing vibrations and the starting phase ascertained during the initialization portion, which leads to a rapid reduction in the disturbing vibrations, while requiring small computational effort.  
         [0012]     The method according to the present invention may use the phase difference as the optimization parameter. This means that the phase difference is changed within an admissible range in such a way that the ascertained amplitude of the current disturbing vibrations is minimized.  
         [0013]     According to the present invention, a monitoring algorithm is provided for switching between initialization portion and compensation portion, which algorithm carries out the switching as a function of certain conditions. This may be implemented by software technology. The conditions are selected, in this instance, in such a way that it is ensured that the compensation signal has no undesired effect on the setting of the valve element. In particular, the functional section, and consequently the application of the compensation signal to the actuating element is terminated, and an initialization portion is initiated anew when certain parameters lie outside predefined ranges and/or the optimization of the phase difference that is carried out leads to no satisfactory result. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  shows a schematic representation of an internal combustion engine having a valve element configured as a throttle valve in an intake port.  
         [0015]      FIG. 2  shows a functional diagram for illustrating the generation of an actuating variable for controlling an actuating device of the throttle valve shown in  FIG. 1 , as well as a compensation signal that is applied to the actuating device.  
         [0016]      FIG. 3  shows a flowchart for illustrating a method for generating the compensation signal.  
         [0017]      FIG. 4  shows a flow chart for illustrating an initialization portion of the method of  FIG. 3 .  
         [0018]      FIG. 5  shows a flow chart for illustrating a compensation portion of the method of  FIG. 3 .  
     
    
     DETAILED DESCRIPTION  
       [0019]     In  FIG. 1 , the overall internal combustion engine bears reference numeral  10 . It includes a motor block  12  having several combustion chambers, which are not individually shown, however, in  FIG. 1 . Combustion air is supplied to these chambers via an intake port  14 , in which there is situated a throttle valve  16 . In this respect, the throttle valve forms a valve element by which the fresh air quantity which reaches the combustion chambers of the internal combustion engine via intake port  14  is able to be adjusted.  
         [0020]     The setting of throttle valve  16  is influenced by an actuating device  18 , for instance, a DC motor or a stepper motor. The current setting of throttle valve  16  is recorded by a position sensor  20 . A rotary speed of a crankshaft  22  of internal combustion engine  10  is recorded by a rotary speed sensor  24 .  
         [0021]     The operation of internal combustion engine  10  is controlled or regulated by a control or regulating device  26 . To do this, among other things, an actuating variable is generated in control or regulating device  26 , which is supplied to actuating device  18 . The actuating variable, among other things, is a function of the signal of position sensor  20 , so that a closed loop control circuit is formed.  
         [0022]     The flow speed inside intake port  14  is subjected to periodic fluctuations which are caused by the discontinuous charging of combustion chambers of internal combustion engine  10 . These fluctuations of the flow speed within intake port  14  are able to lead to undesired vibrations within intake port  14  (“disturbing vibrations”) of throttle valve  16 .  
         [0023]     As may be seen in  FIG. 2 , an actuating variable S is supplied to actuating device  18 , which variable S is composed of a positioning signal S pos  and a compensation signal S comp . Positioning signal S pos  is generated within the scope of a closed loop control circuit in a control block  28 . Into control block  28  there is fed, among others, a signal S ist  (actual quantity) that corresponds to the setting of throttle valve  16 , this signal being made available by position sensor  20 , and a signal S soll  (setpoint quantity) that corresponds to a desired setting of throttle valve  16 . The latter is determined, for example, as a function of a desired torque of internal combustion engine  10 .  
         [0024]     Compensation signal S comp  is determined in block  30  shown in  FIG. 2 , based on the current rotary speed nmot of crankshaft  22  of internal combustion engine  10 , which speed nmot is ascertained by sensor  24 , as well as based on actual quantity S ist  and setpoint quantity S soll . Position changes of throttle valve  16 , which are provoked by the above-named flow fluctuations in intake port  14 , are compensated for or at least reduced by compensation signal S comp .  
         [0025]     In block  30 , for the generation of compensation signal S comp , the method proceeds in two portions that are separate from each other (see  FIG. 3 ): in an initialization portion  32 , starting (or initial) variables A ini  and P ini  are determined for the ascertainment of compensation signal S comp . As long as initialization portion  32  is running, a compensation signal S comp  is not output. In a compensation portion  34 , the actual parameters A comp , F comp , dP comp  of compensation signal S comp  are ascertained and compensation signal S comp  is output. A comp  is the amplitude, F comp  is the frequency and dP comp  is the phase difference of compensation signal S comp  with respect to the disturbing vibrations.  
         [0026]     The execution of initialization portion  32  will now be explained in greater detail, with reference to  FIG. 4 . In initialization portion  32  a starting amplitude A ini  and a starting phase P ini  of the current disturbing vibrations are ascertained. To do this, first, in a block  36 , the difference between the two signals S ist  and S soll  is formed (“difference signal”), and from this the absolute quantities are formed. In block  38 , the maximum values that come about are recorded, and in block  40  signals formed from the maximum values are low-pass filtered. Finally, the starting amplitude is obtained by this nonlinear processing of signals S ist  and S soll .  
         [0027]     A similar nonlinear processing leads to starting phase P ini  in  42 . For this, the last zero crossing before the end of initialization portion  32  of the absolute quantity of the difference signal determined in block  36  is recorded, and the starting phase that is determined is stored as reference value for periodic compensation signal S comp .  
         [0028]     The sequence of compensation portion  34  may be seen in detail in  FIG. 5 . Compensation portion  34  includes three steps: in a first step  44 , the properties of the current disturbing vibrations are ascertained or updated. In the problem at issue, this refers to frequency F and amplitude A of the disturbing vibrations. The disturbing vibrations in intake port  14  considered in the present case are caused, as was explained above, by the discontinuous charging of the individual combustion chambers of internal combustion engine  10 . The charging is directly coupled to rotary speed nmot of internal combustion engine  10 , which, in turn is recorded by sensor  24 . Therefore, frequency F of the disturbing vibrations is gathered in the present exemplary embodiment directly from current rotary speed nmot of crankshaft  22  of internal combustion engine  10 . Amplitude A of the current disturbing vibrations is obtained, in turn, analogously to the method explained in connection with  FIG. 4 .  
         [0029]     In a second step  46  within compensation portion  34 , the properties and parameters F comp , A comp  and dP comp  of periodic compensation signal S comp  are determined, based on the parameters which were ascertained during initialization portion  32  and during first step  44  within compensation portion  34 .  
         [0030]     Frequency F comp  of compensation signal S comp  is set equal to frequency F of the disturbing vibrations that was ascertained in first step  44 . Amplitude A comp  of periodic compensation signal S comp  is determined with the aid of a formula based on amplitude A ini , which was ascertained during initialization portion  32 , and frequency F. In the present exemplary embodiment, the formulaic connection in  48  is implemented by processing the elements of a look-up table. The elements of the look-up table, in turn, were obtained by a frequency analysis of values ascertained on a test stand.  
         [0031]     Phase difference dP comp  is obtained by an on-line optimization in  49 . For this purpose, in the present exemplary embodiment, compensation signal S comp  is changed starting from a starting value dP ini  in such a way that amplitude A of the disturbing vibrations, ascertained in  44 , decreases. Starting value dP ini  for the phase difference is ascertained from a formula that is based on phase position P ini , which was ascertained during initialization portion  32 , and frequency F. Here, too, the implementation of the formulaic connection in  50  takes place by the processing of values stored in a look-up table. These values, in turn, were obtained from such values that were measured on a test stand, using frequency analysis.  
         [0032]     Compensation portion  34  having online optimization  49  is carried out repeatedly in iterative fashion, so as to optimize phase difference dP comp  of compensation signal S comp , starting from starting value dP ini  in such a way that amplitude A of the disturbing vibrations tends to a minimum. In the present case, a gradient-based algorithm is used as the online optimization algorithm.  
         [0033]     A third step (reference numeral  52 ) in  FIG. 5  of compensation portion  34  includes the determination and output of actual compensation signal S comp , based on ascertained parameters A comp , F comp  and dP comp . The ascertainment of compensation signal S comp  is based on a time-periodic mathematical function that is characterized by frequency, amplitude and phase. In the present case, a square-wave signal  54  is selected for this time-periodic function.  
         [0034]     The switchover between initialization portion  32  and compensation portion  34  takes place using a monitoring algorithm  56 . Switchover is carried out from initialization portion  32  to compensation portion  34  when properties A ini  and P ini , that are required for compensation portion  34 , of the current disturbing vibrations of throttle valve  16  have been recorded and ascertained.  
         [0035]     The switchover in the opposite direction, that is, from compensation portion  34  to initialization portion  32 , takes place when compensation signal S comp  can no longer compensate for, or reduce the disturbing vibrations in the desired manner. This is detected in the present exemplary embodiment when frequency F and/or amplitude A lie outside a certain frequency range and amplitude range. The same applies to the case in which the absolute setting of throttle valve  16  lies outside a certain range. Finally, a switchover takes place from compensation portion  34  to initialization portion  32  when the online optimization of phase difference dP comp  in  49  is not (any longer) in a position significantly to reduce amplitude A of the disturbing vibrations. An appropriate boundary value is able to be used for this too.