Abstract:
A method and control system are disclosed for controlling an internal combustion engine having fuel injector(s), a camshaft for actuating inlet and/or outlet valve(s), a valve-train adjusting device for controllable switchover between different valve actuating characteristics, and optionally a camshaft sensor which supplies a camshaft signal representing the camshaft angle, a crankshaft sensor which supplies a crankshaft signal representing the crankshaft angle, and a control unit which controls the fuel injectors to inject predetermined fuel quantities at predetermined injection instants, wherein these stipulations take place as a function of the switching state of the valve-train adjusting device. To obtain information about this switching state, cylinder pressure signal(s) supplied by a cylinder pressure sensor are evaluated with regard to interference signals, and the evaluation result is used in determining the switching state of the valve-train adjusting device for stipulating the fuel quantities to be injected and/or the injection instants.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application of International Application No. PCT/EP2011/061331 filed Jul. 5, 2011, which designates the United States of America, and claims priority to DE Application No. 10 2010 027 214.0 filed Jul. 15, 2010, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a method and a control unit for controlling an internal combustion engine. 
         [0003]    The disclosure thus relates in particular for example to the control of an applied-ignition or diesel engine which is used as a drive source in a conventional motor vehicle or as one of multiple drive sources in a hybrid vehicle. 
         [0004]    The valve drive adjustment device used in the case of such control for controllable switching between at least two different actuation characteristics (“lift curves”) of at least one valve (inlet valve or outlet valve) which is actuated by means of a camshaft advantageously permits a reduction in fuel consumption and/or an increase in power in relation to internal combustion engines without a valve drive adjustment device. 
       BACKGROUND 
       [0005]    Valve drive adjustment devices in internal combustion engines for motor vehicles are known in a variety of applications. Three are mentioned here by way of example. In the case of the “Valvetronic” adjustment device (BMW), an actuating mechanism arranged between a camshaft and a valve tappet is adjusted by means of an electric actuating motor and an eccentric shaft in order to realize a variable (maximum) valve lift as a function of certain operating parameters of the internal combustion engine. Said adjustment of the valve lift may be combined with a so-called camshaft phase adjustment in which a relative adjustment of the crankshaft and camshaft with respect to one another, and thus a variation of the valve timing, is also performed as a function of the operating state of the internal combustion engine. The “VTEC” (Honda) adjustment device exists in different variants which have in common the fact that a switch between different actuation characteristics takes place as a function of certain parameters of engine operation. In the “Ti-VCT” (Ford) adjustment device, adjustment by means of hydraulic actuators is provided. The adjustment is performed in a continuously variable fashion as a function of engine load by means of electronic characteristic-map-based control. The three abovementioned adjustment devices are controlled in each case by an electronic engine control unit which also actuates the fuel injectors for the injection of predefined amounts of fuel. It is however also possible for such valve drive adjustment devices to be actuated autonomously, or by means of a control device which is independent of the actual engine control unit, during engine operation. Conceivable for this purpose are for example hydraulic actuators (charged for example with engine oil pressure), pneumatic actuators or for example centrifugal force adjusters (for example for crankshaft rotational speed dependency). 
         [0006]    The known valve drive adjustment devices may furthermore be divided into two categories with regard to variability of adjustment, specifically discontinuously variable systems and continuously variable systems. 
         [0007]    A discontinuously variable system may for example be constructed such that a plurality of different profiles per valve is provided on the camshaft. Each profile results in a different lift curve for the valve, wherein at all times only one profile can be active, and switching between the different profiles can be performed. In concepts of said type, a change in the lift curve is performed abruptly. 
         [0008]    In relation thereto, continuously variable systems offer more comprehensive variability of the valve drive. Since said systems permit a continuous variation of the valve actuation characteristic, they thus eliminate for example the difficulties that otherwise result from an abrupt switch. Continuous systems are used in particular for low-loss load control of internal combustion engines. It is for example possible for the air or mixture supply to the combustion chamber to be controlled by means of the variability of the lift curve of an inlet valve. 
         [0009]    In particular in the case of discontinuously variable systems which thus provide an abrupt switch between different actuation characteristics, a corresponding change in the parameters used for the control of the engine should, for optimum control of the combustion, take place equally abruptly. Such parameters include for example the parameters used for the predefinition (calculation) of the amounts of fuel to be injected and/or of the injection times and crank angles. To be able to switch the engine control at the “correct time”, the control unit however requires reliable information regarding the present switching state of the valve drive adjustment device. Said information must be kept permanently “up to date” and/or correspondingly updated upon a change in the switching state. If a switch of the valve drive adjustment device takes place for example at an arbitrary time during sequential operation of a multi-cylinder internal combustion engine, the changed predefinition of the parameters should thus ideally take effect immediately for the engine control operations following said time, in particular for the relevant control process (for example ignition, injection etc.) of the “next cylinder” (in the operating sequence) at the latest. Precise information regarding the switching state of the valve drive adjustment device is thus required in order to optimally control the combustion. 
         [0010]    Such information could duly be obtained by means of a position sensor installed on the valve drive adjustment devices, which position sensor outputs to the control unit a position sensor signal representing the present switching state of the adjustment device. 
         [0011]    Such a position sensor signal could then be taken into consideration by the electronic engine control unit as input information for the determination of the switching state of the valve drive adjustment device. 
         [0012]    The arrangement of a position sensor on the valve drive adjustment device would however disadvantageously entail a certain amount of outlay in terms of construction, in particular if it were sought for the sensor signal output by said position sensor to represent the actual present switching state with high accuracy. 
       SUMMARY 
       [0013]    One embodiment provides a method for controlling a single-cylinder or multi-cylinder internal combustion engine having: at least one fuel injector per cylinder for injecting fuel, at least one camshaft for actuating at least one inlet valve and/or at least one outlet valve, wherein a valve drive adjustment device is provided for controllable switching between at least two different actuation characteristics of at least one valve that is actuated by means of the camshaft, a crankshaft sensor which outputs a crankshaft signal which represents the crankshaft angle, and a control unit which controls the fuel injectors such that amounts of fuel predefined by the control unit are injected by said fuel injectors at injection times predefined by the control unit, wherein said predefinitions are performed as a function of the switching state of the valve drive adjustment device, wherein at least one cylinder pressure signal output by a cylinder pressure sensor for measuring the pressure in an associated cylinder is evaluated with regard to interference signals, and in that the evaluation result is taken into consideration in a determination of the switching state of the valve drive adjustment device for the predefinition of the amounts of fuel to be injected and/or of the injection times. 
         [0014]    In a further embodiment, the actuation characteristics differ from one another with regard to a maximum valve stroke. 
         [0015]    In a further embodiment, the actuation characteristics differ from one another with regard to a camshaft phase. 
         [0016]    In a further embodiment, a camshaft signal output by a camshaft sensor as a function of a camshaft angle is taken into consideration in the evaluation of the cylinder pressure signal. 
         [0017]    In a further embodiment, the internal combustion engine has a plurality of cylinders and the cylinder pressure signals of cylinder pressure sensors respectively assigned to all of the cylinders are taken into consideration. 
         [0018]    In a further embodiment, the evaluation result is furthermore used for checking the plausibility of the crankshaft signal output by the crankshaft sensor and/or of the camshaft signal output by the camshaft sensor. 
         [0019]    Another embodiment provides a control unit for controlling a single-cylinder or multi-cylinder internal combustion engine having: at least one fuel injector per cylinder for injecting fuel, at least one camshaft for actuating at least one inlet valve and/or at least one outlet valve, wherein a valve drive adjustment device is provided for controllable switching between at least two different actuation characteristics of at least one valve that is actuated by means of the camshaft, a crankshaft sensor which outputs a crankshaft signal which represents the crankshaft angle, and the control unit which controls the fuel injectors such that amounts of fuel predefined by the control unit are injected by said fuel injectors at injection times predefined by the control unit, wherein said predefinitions are performed as a function of the switching state of the valve drive adjustment device, wherein the control unit is designed to evaluate with regard to interference signals at least one cylinder pressure signal output by a cylinder pressure sensor for measuring the pressure in an associated cylinder, and to take the evaluation result into consideration in a determination of the switching state of the valve drive adjustment device for the predefinition of the amounts of fuel to be injected and/or of the injection times. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Exemplary embodiments will be explained in more detail below based on the schematic drawings, wherein: 
           [0021]      FIG. 1  shows a schematic sectional illustration of an internal combustion engine in the form of a 4-stroke applied-ignition engine, 
           [0022]      FIG. 2  shows an illustration of a cylinder pressure signal profile as a function of the crank angle in the engine of  FIG. 1 , 
           [0023]      FIG. 3  shows a plot of the high-pass-filtered cylinder pressure signal versus the crank angle, 
           [0024]      FIG. 4  shows two cylinder pressure signal profiles in an illustration corresponding to  FIG. 2 , for two different switching states of a valve drive adjustment device in the engine of  FIG. 1 , and 
           [0025]      FIG. 5  shows an illustration of different valve lift curves as a function of the crank angle and the switching state of the valve drive adjustment device in the engine of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Embodiments of the present disclosure may simplify the obtaining of information regarding the present switching state or the present setting of the valve drive adjustment device, e.g., to thereby permit a rapid and precise change in the injection amount predefinition (and possibly of further control processes and/or parameters for this purpose) as a result of a change in the switching state of the valve drive adjustment device. 
         [0027]    In some embodiments, at least one cylinder pressure signal output by a cylinder pressure sensor for measuring the pressure in an associated cylinder is evaluated with regard to interference signals, and in that the evaluation result is taken into consideration in a determination of the switching state of the valve drive adjustment device for the predefinition of the amounts of fuel to be injected and/or of the injection times. 
         [0028]    Said evaluation result can itself be used as a “sensor signal” which represents the present setting of the valve drive adjustment device. Said evaluation result may however also be supplied to the control unit in addition to a position sensor signal, either for example in order to realize redundancy in the determination of the present setting or for example to realize an improvement in the accuracy of said determination. A further advantage consists in that the evaluation result can furthermore be used for performing a diagnosis with regard to correct functioning of the valve drive switching. If for example a switch is triggered by means of the control unit but the evaluation result does not reflect a correct actual adjustment (switch), a fault is present, upon the detection of which a suitable warning can be generated and/or an entry can be made in a diagnostic memory. 
         [0029]    Cylinder pressure sensors are known per se in the field of engine technology and serve for measuring the cylinder pressure. In conventional systems, the cylinder pressure signal is used only for evaluating the combustion. It is thus possible, for example, for errors in the metering of the fuel, of the air mass or of a recirculated combustion gas fraction to be determined and/or corrected. In the case of a multi-cylinder internal combustion engine, it is the case in conventional systems that for this purpose either only a single cylinder pressure sensor at one of the cylinders is taken into consideration as a representative of all of the cylinders collectively, or alternatively a separate cylinder pressure sensor is provided for each cylinder. 
         [0030]    The present inventors have now identified that such cylinder pressure sensors normally have such high sensitivity and/or such a high resolution for the measurement of the cylinder pressure that they are also sensitive to interference noises which propagate (as body-borne sound) through a for example metallic cylinder block. The basic concept is for the interference signals, caused by such interference noises, in one or more cylinder pressure signals detected by one or more cylinder pressure sensors to be utilized as a source of information regarding the engine state, in particular the state of the valve drive adjustment device. If one or more camshafts rotate in order thereby to realize the valve drive (opening and closing of inlet and outlet valves), noises are generated which lead to characteristic interference signals in the one or more cylinder pressure signals. By means of the evaluation of the (at least one) cylinder pressure signal with regard to such disturbance signals, it is thus advantageously possible to draw conclusions regarding the present setting. 
         [0031]    This is achieved for example through the use of suitably predetermined evaluation criteria, on the basis of which, in the engine control unit, an identification of processes in the valve drive takes place, and subsequent determination of the present setting on the basis of the previously identified processes in the valve drive. 
         [0032]    One possible identification criterion may for example consist in detecting sudden changes, for example discontinuities or “signal peaks” in the measured pressure profile, and assigning them on the basis of the characteristic thereof (for example amplitude, frequency components, duration etc.) and/or on the basis of additional information regarding the engine position (for example crankshaft signal, camshaft signal etc.) to a very particular process in the valve drive (for example valve opening or valve closing process). Such an approach is significantly easier, faster and often more precise than for example an evaluation on the basis of a comparison of the measured pressure profile (cylinder pressure signal) with previously stored typical pressure profiles. 
         [0033]    In particular, the evaluation may encompass an identification of times and/or crank angles at which inlet valves and/or outlet valves are opened or closed. For said evaluation step, it is for example possible for interference signals caused by the relevant valves upon the actuation thereof to be detected. 
         [0034]    An interference signal which occurs in particularly pronounced form in practice and which is thus relatively easy to detect by evaluation arises for example at the end of a closing process of a valve (inlet or outlet valve). The setting down, which occurs at that time, of a valve body (for example a valve plate) onto a sealing surface in the region of a wall which delimits the associated cylinder leads to a mechanical vibration which manifests itself very clearly as an interference signal (for example “signal peak”) in the actual useful signal (representative of the cylinder pressure). 
         [0035]    In the case of a multi-cylinder internal combustion engine, it may be preferable, in particular with regard to a simple and reliable identification of the valve which has generated a certain interference signal, for the cylinder pressure signals of cylinder pressure sensors respectively assigned to all of the cylinders to be evaluated. For this purpose, each cylinder must be provided with at least one cylinder pressure sensor, which may be installed for example in the region of a respective cylinder head. 
         [0036]    It is basically possible for the noises of the opening and of the closing of the inlet valve and also of the outlet valve to be detected by means of one cylinder pressure sensor and suitable evaluation of the cylinder pressure signals output thereby. For the determination of the present setting (switching state) of the valve drive adjustment device during engine operation, it is accordingly possible to take into consideration in particular the times of interference signals generated by an opening or a closing of an inlet valve or of an outlet valve. The respective magnitude of the interference signals generated thereby is dependent for example on the specifically selected installation position of the sensor. By means of corresponding installation of the cylinder pressure sensor, for example closer to an inlet valve than to an outlet valve of the respective cylinder, it is possible for interference signals firstly of the inlet valve and secondly of the outlet valve to be generated which can be distinguished from one another qualitatively and/or quantitatively within the context of the evaluation, such that it is advantageously possible for the valve that is generating a certain interference signal to be identified in a simple manner (for example on the basis of the interference signal amplitude). 
         [0037]    If the evaluation result taken into consideration as an input variable for the determination of the switching state of the valve drive adjustment device concerns the times or crank angles at which a certain valve opening process begins or valve closing process ends, it is possible in the control unit for a determination of the present switching state of the adjustment device to be realized for example in that, on the basis of a predetermined algorithm (for example by means of a characteristic map or the like stored in the control unit), conclusions are drawn regarding the profile of the valve actuation process as a whole (“lift curve”). The information regarding the profile of the lift curve (for example as a function of the crank angle) is however equivalent to information regarding the present setting (switching state) of the adjustment device. 
         [0038]    A prerequisite for the functioning of said method of determining the present setting may be a predefined relationship between the valve timing (for example the times and/or crank angles at which a valve opening process begins or a valve closing process ends) and/or the valve opening duration on the one hand and the present setting of the valve drive adjustment device on the other hand. 
         [0039]    Said prerequisite is fulfilled for example when the variable setting is represented by at least two (or more) lift curves which differ in terms of their timing in a plot of the valve lift versus the crank angle. In this case, different valve timings yield different lift curves, such that, taking into consideration the specific mode of operation of the valve drive adjustment device, it is possible with the knowledge of said valve timing to infer the then uniquely associated lift curves (synonymous with: switching state of the valve drive adjustment device). The latter inference may be performed for example using suitable evaluation software in the control unit, by means of which the previous determination of the valve timing is also performed. 
         [0040]    It may thus be possible to obtain information regarding the present setting of said adjustment device independently of a position sensor which is if appropriate provided in the region of the valve drive adjustment device. It is thus possible in particular to dispense with a position sensor provided specifically for this purpose. The “incorrect use” of at least one cylinder pressure sensor within the context of this disclosure does not in any way rule out that the one or more cylinder pressure signals gained are also used in the “conventional way”, that is to say for assessing the combustion quality in engine operation. 
         [0041]    In one embodiment, it is provided that the change (switch) of the actuation characteristic of the respective valve encompasses a valve lift adjustment. This means that the valve drive adjustment device can be actuated so as to attain different maximum valve strokes. In this case, the different actuation characteristics differ from one another with regard to a maximum valve stroke. 
         [0042]    It may alternatively or additionally be provided that the change (switch) of the actuation characteristic of the respective valve encompasses a camshaft phase adjustment. This means, in a broader sense, that the valve drive adjustment device can be switched in order to change the valve timing of the respective valve. In a narrower sense, the “camshaft phase adjustment” may refer to the relative rotation, which is suitable for this purpose, between the camshaft and the crankshaft. In this case, the actuation characteristics differ from one another with regard to a camshaft phase. 
         [0043]    In one embodiment which combines the abovementioned options, the change of the actuation characteristic caused by the switch encompasses both a valve lift adjustment and also a cam phase adjustment (that is to say a change in the timing) of the respective valve. 
         [0044]    In one embodiment, a switch between two different actuation characteristics of the respective valve is provided, wherein at least the (maximum) valve lift is changed by the switch. 
         [0045]    In conventional internal combustion engines, a camshaft sensor is provided which outputs a camshaft signal which is dependent on the camshaft angle. In this regard, however, it is necessary to point out the possibility, which is conceivable in principle within the context of this disclosure, of dispensing with the use of a camshaft sensor, and of the camshaft signal output thereby, in the determination of the camshaft angle. It is in principle conceivable to use for this purpose the evaluation result regarding the interference signals of the cylinder pressure signal. 
         [0046]    In an embodiment in which a camshaft sensor is provided, a present setting of the valve drive adjustment device may be determined for example by virtue of a time or crank angle, detected on the basis of the evaluation result, of a certain event of a valve actuation process being set in relation to a time or crank angle, detected on the basis of the camshaft signal, of another certain event of the same valve actuation process. 
         [0047]    The time detected on the basis of the evaluation result may in particular be the time (synonymous with crank angle) at which a certain valve closes (setting-down of a valve body on a valve sealing surface). Said time may for example be set in relation to the time or crankshaft angle, determined on the basis of the camshaft signal (usually jointly taking into consideration the crankshaft signal), at which the valve opening process previously began. From said two times and/or crank angles, it is then possible by simple difference calculation to determine (calculate) the time period or crank angle difference between the start and the end of the valve actuation. From said difference, it is then possible, again using a suitable software algorithm or previously stored data (for example characteristic map), to infer the present setting (switching state) of the valve drive adjustment device. 
         [0048]    Said method for determining the present setting functions for example when the variability of the valve drive adjustment device is realized such that the opening time remains the same for the different lift curves (and only the closing time (and if appropriate maximum stroke) is changed by the switch). In this case, there are always different time or crank angle differences between the start and the end of the valve actuation for different lift curves. As an alternative to a determination of the present switching state on the basis of said difference, said determination may also take place on the basis of the closing time alone. 
         [0049]    Said method of also determining the associated lift curve or the switching state of the valve drive adjustment device on the basis of a determination of a valve closing time is however also possible for example when the switch of the adjustment device is associated with a change not of the valve closing time but rather only of the (maximum) valve stroke. Specifically, in this case, the interference noise resulting from the setting-down of the valve body (for example valve plate) onto the respective valve sealing surface (for example inlet opening on a cylinder head) will generally vary as a function of the previously attained valve lift. This is the case for example owing to a speed with which the valve body impacts against the sealing surface, said speed being dependent on the maximum valve stroke reached previously. Since such differences in the generated noise or body-borne sound can however be detected in the evaluation of the cylinder pressure signal, it is possible in this case, too, to draw corresponding conclusions regarding the maximum valve stroke reached previously and thus the setting (switching state) of the valve drive adjustment device. 
         [0050]    As already mentioned, it is conceivable within the context of this disclosure to dispense with a camshaft sensor provided for determining the camshaft angle. However, if a camshaft sensor of said type is provided, then the determination of the camshaft angle as performed by the control unit may advantageously be realized within the context of this disclosure for example additionally taking into consideration the evaluation of the cylinder pressure signal. 
         [0051]    The information regarding whether and how fast the crankshaft is rotating is gained, in known engines, on the basis of the crankshaft signal. Said crankshaft signal is normally a “toothed signal”: each pulse of the crankshaft signal corresponds to a tooth of an encoder wheel which is provided with a multiplicity of teeth. A synchronization pulse provided for in each case one crankshaft revolution (360°) normally corresponds to a single or double “tooth space” after the corresponding number of teeth. 
         [0052]    The camshaft signal serves for encoding the camshaft angle and, in the simplest case, has two different levels which are assigned to two successive revolutions of the camshaft. The camshaft signal may however also have other signal or pulse shapes. It should however be ensured that the camshaft signal permits a division of each working cycle of the engine into two segments (of in each case 360°) corresponding to two successive crankshaft revolutions) (720°). 
         [0053]    Such crankshaft signals and camshaft signals which are known per se may advantageously also be provided within the context of this disclosure (cf. for example DE 100 56 862 C1). 
         [0054]    In one embodiment, it is provided that the evaluation result is used for checking the plausibility of the crankshaft signal output by the crankshaft sensor and/or of the camshaft signal output by the camshaft sensor. It is thus possible, for example, for the situation of an erroneous (defective) generation of the crankshaft signal and/or of the camshaft signal to be diagnosed and stored for example as a fault entry in a diagnostic memory such as is conventional in motor vehicles. The plausibility check may alternatively or additionally also be used for diagnosing any assembly errors, for example incorrectly assembled camshaft drives such as toothed belts or chains. 
         [0055]    Alternatively or in addition, the mentioned plausibility check of the crankshaft and/or camshaft signal may be used for further purposes. 
         [0056]    For example, in one refinement, it is provided that the result of the evaluation of the cylinder pressure signal with regard to interference signals is used, in the event of the detection of an implausible crankshaft signal, as a replacement for said crankshaft signal or for correcting said crankshaft signal and/or, in the event of the detection of an implausible camshaft signal, as a replacement for said camshaft signal or for correcting said camshaft signal. 
         [0057]    In particular, the evaluation result can thus also be used for rotational speed calculation and/or for realizing emergency running in the case of a defective crankshaft sensor or in the event of a defect in the area of the provision of the crankshaft signal (to the control unit). The same applies for the situation of a defective camshaft sensor or an erroneous provision of the camshaft signal. 
         [0058]    A further possibility of interest consists in taking the evaluation result into consideration for the identification and then optionally also adaptation of deviations in the valve drive or the valve drive adjustment device as a result of component tolerances and/or aging. Component tolerances and/or aging can result in particular in a deviation of the design-intended times and/or angles for valve opening processes and valve closing processes. In this case, the information gained only on the basis of the camshaft signal and/or of a position sensor signal of the valve drive adjustment device would be inaccurate as regards the times and/or angles of the actual opening and closing processes. Since the actual opening and/or closing processes of the valves can however be detected by means of the evaluation of the cylinder pressure signal with regard to disturbance signals, the evaluation result constitutes an information source, which is extremely valuable in practice, for the engine control and in particular the determination of the switching state of the valve drive adjustment device. 
         [0059]    By virtue of the consideration of the result of the evaluation of the cylinder pressure signal with regard to the interference signals (or joint consideration in addition to a crankshaft signal and/or camshaft signal), the cylinder pressure signal provides additional benefit for a determination of the present setting of valve drive adjustment devices such as for example discontinuously variable systems in which, for the respective valve, different profiles are provided on the camshafts, wherein a switch can be made between the different profiles. It is advantageously possible for the evaluation result gained on the basis of the cylinder pressure signal to be utilized in particular for determining the exact (actual) present function of the valve drive adjustment device. The evaluation result yields precise times of the relevant processes in the valve drive, which times can serve as valuable current information for further processing or utilization, which is otherwise implemented for example in the conventional manner, of the information regarding the switching state. 
         [0060]    A control unit used for controlling the internal combustion engine may be provided in the conventional manner as an electronic, in particular program-controlled control unit (for example microcontroller). However, the control unit may be further developed (for example by means of a corresponding modification of the control software) such that a control method of the type described above is carried out. 
         [0061]      FIG. 1  illustrates an internal combustion engine  10  which, in this case, is for example a four-cylinder 4-stroke applied-ignition engine. 
         [0062]    Each cylinder  12  is assigned at least one injection valve or fuel injector  14  for injecting fuel (in this case gasoline) into an inlet-side intake pipe of the internal combustion engine  10 . 
         [0063]    Furthermore, each cylinder  12  is assigned in each case at least one inlet valve  16  and at least one outlet valve  18  and also at least one camshaft for actuating the inlet and outlet valves. In the exemplary embodiment illustrated, a camshaft  20  is provided for actuating the inlet valves  16  and a further camshaft (not illustrated) is provided for actuating the outlet valves  18 . 
         [0064]    In a manner known per se, there is a rotationally coupled connection between the camshafts and a crankshaft  22 , said rotationally coupled connection being realized for example by means of a timing chain or the like and ensuring that, during operation of the internal combustion engine  10 , the camshafts rotate at half of the rotational speed of the crankshaft  22 , in order thereby to realize a working cycle or a gas exchange as per the 4-stroke cycle. 
         [0065]    Into an electronic control unit  24  there are input inter alia a camshaft signal CAM which is dependent on the rotational position of the camshaft  20  and a crankshaft signal CRK which is dependent on the rotational position of the crankshaft  22 . Said signals CAM and CRK are generated by means of suitable sensors, in this case a camshaft sensor  26  and a crankshaft sensor  28 . 
         [0066]    In a manner known per se, the signals CAM and CRK are generated in each case as rectangular signals. 
         [0067]    Each pulse of the crankshaft signal CRK corresponds to a tooth of an encoder wheel, wherein a double tooth space provides a synchronization pulse after in each case one full revolution) (360° of the crankshaft  22 . There are typically for example 30 or 60 teeth (minus the teeth omitted at the “gap”) arranged on the circumference of the encoder wheel. 
         [0068]    The two different levels of the camshaft signal CAM correspond to two successive revolutions of the crankshaft  22 . 
         [0069]    With regard to said encodings of the rotational positions of the crankshaft  22  and of the camshaft  20 , reference is hereby made for example to the German patent DE 100 56 862 C1, in which time profiles of such signals CRK and CAM which arise during engine operation are schematically illustrated and described in more detail. 
         [0070]    During operation of the internal combustion engine  10 , the electronic control unit  24  controls in particular the injection of fuel (injection times and injection amounts) into the cylinders  12  by means of the respectively associated fuel injector  14  (actuation signal INJ). Furthermore, the control unit  24  also controls other processes of the internal combustion engine  10 , such as in this case in particular an applied ignition (ignition times) by means of an ignition plug respectively assigned to each cylinder  12  (high-voltage pulse IGN). 
         [0071]    A valve drive adjustment device  21  shown symbolically in  FIG. 1  serves for controllably changing the actuation characteristic of the valve (in this case inlet valve  16 ) which is actuated by means of the camshaft  20 . 
         [0072]    It is duly the case in the illustrated exemplary embodiment, too, that there is a fixed angular assignment between the camshaft  20  and crankshaft  22  as a result of a rotationally conjoint coupling (whereby the camshaft  20  rotates at half of the rotational speed of the crankshaft  22 ). 
         [0073]    The actuation of the inlet valve  16  is however realized not directly or indirectly by means of an invariable mechanism (for example simple rocker arm etc.) but rather, as illustrated in  FIG. 1 , by means of the valve drive adjustment device  21  which can be controlled by means of an adjustment signal VADJ output by the control unit  24 . It is thereby possible for the actuation characteristic, that is to say in this case the relationship between the present rotational angle position of the camshaft  20  (camshaft angle) and present valve lift VLFT (cf.  FIG. 5 ) of the valve  16 , to be switched. In the example illustrated, only two different actuation characteristics for said valve  16  are provided, specifically one with relatively large (maximum) valve lift and one with relatively small (maximum) valve lift. In the illustrated example, in the event of a switch between said two actuation characteristics, the start of the valve actuation in terms of crank angle is not changed but rather only the maximum valve lift attained during the course of the valve actuation and the time duration of the valve actuation (and thus the end of the valve actuation in terms of crank angle) are changed. 
         [0074]      FIG. 5  shows the corresponding lift curves L 16 - 1  (for the inlet valve  16 , with large lift) and L 16 - 2  (for the inlet valve  16 , with small lift).  FIG. 5  also shows a lift curve L 18  for the outlet valve  18 . In particular for optimum predefinition of the injection times and/or of the amounts of fuel to be injected as a function of the present switching state of the valve drive adjustment device  21 , it is necessary to obtain the most precise possible information regarding the present setting of the valve drive adjustment device  21 . For this purpose, there could be provided for example a corresponding “position sensor” which, as symbolized in  FIG. 1  by the dashed line, outputs a corresponding sensor signal to the control unit  24 . It is pointed out already at this juncture that such a position sensor can be omitted from the illustrated internal combustion engine  10  because the present setting (switching state) of the valve drive adjustment device  21  can, as described here, be determined in a different way. 
         [0075]    It is the purpose of the switching of the valve actuation characteristic to vary the valve timing (for example in order to vary the so-called valve overlap) as a function of one or more operating parameters of the respective engine (load, rotational speed, etc.) and/or to vary the (maximum) valve lift as a function of such operating parameters.  FIG. 5  illustrates the change of the actuation characteristic provided in the described exemplary embodiment, wherein both the valve actuation duration and also the valve lift of the inlet valve  16  are varied. 
         [0076]    By means of the adjustment signal VADJ generated by the control unit  24  in accordance with an algorithm for controlling the device  21 , it is for example possible for this purpose for an electromechanical or electrohydraulic actuator, which as a control element for switching between the two actuation characteristics (corresponding to the lift curves L 16 - 1  and L 16 - 2  in  FIG. 5 ) is arranged in the valve drive adjustment device  21 , to be actuated. 
         [0077]    The change in the actuation characteristic (in this case for the inlet valve  16 ) effected by the switch could, by contrast to the illustrated example, also be realized by means of a control device which is independent of the control unit  24 . For this purpose, consideration is for example given to using a hydraulic switching mechanism for switching as a function of an engine oil pressure. 
         [0078]    If, by contrast to the illustrated example, it is the intention for a change in the valve timing (early shift or late shift) to be effected with the change of the actuation characteristic, this could also be realized by means of a valve drive adjustment device in the form of a so-called “phase converter” by means of which a rotation of the respective camshaft (in this case camshaft  20 ) relative to the crankshaft (and/or relative to a further camshaft) is effected for example in a load-dependent and/or rotational-speed-dependent manner. Such adjustment systems are the most widely used variable valve controllers in series use in motor vehicle engines. In the case of such special adjustment devices (phase converters), the cam profiles themselves and therefore the maximum valve lift and the valve opening duration usually remain unchanged. 
         [0079]    After an initiation of the switch of the actuation characteristic by means of the adjustment signal VADJ, a certain amount of time passes before the new actuation characteristic actually takes effect. Said time is dependent on a multiplicity of factors. These include not only the engine parameters such as for example the rotational speed, for which accurate information is present in the engine control unit, but rather also factors for which no such information is present. Since the time between the initiation of the new actuation characteristic and the time at which the new actuation characteristic takes effect therefore varies in practice and cannot be predicted very exactly, the initiating actuation signal VADJ itself does not constitute a “sensor signal” that would permit a precise prediction for the time of the actual switch of the valve drive. It must furthermore be considered that deviations between the design-intended actuation characteristic and the actuation characteristic actually realized may arise over the course of time for example as a result of tolerances and aging phenomena. The latter problem could in principle be solved by means of the abovementioned “position sensor”. This is however associated with corresponding outlay in terms of construction for the provision of the position sensor signal, in particular if said signal is intended to represent the present setting of the valve drive adjustment device with high accuracy. 
         [0080]    Said problem is solved in the case of the illustrated internal combustion engine  10  in that each of the cylinders  12  is assigned a cylinder pressure sensor  32  which outputs to the control unit  24  a cylinder pressure signal P (cf.  FIG. 2 ) which represents the present cylinder pressure. By means of the engine control software which is executed in the control unit  24 , the cylinder pressure signal P is taken into consideration for the evaluation of the combustion in the cylinders  12 , and based thereon, for the metering of the fuel, of the air mass or of a combustion gas fraction to be recirculated. For the solution of the problem explained above, however, it is crucial that the control unit  24  also performs an evaluation of the cylinder pressure signal P with regard to interference signals contained therein, and that the result of said evaluation is taken into consideration as an input variable for the determination of the switching state of the valve drive adjustment device  21 . As explained below, said interference signals allow conclusions to be drawn regarding the positions of the valves and thus also for example regarding the present setting of the valve drive adjustment device  21 . 
         [0081]    Each cylinder pressure sensor  32  may advantageously be constructed, and function, in accordance with any known pressure measurement principles. Although the sensor signal P output thereby is determined primarily by the pressure prevailing in the respective cylinder  12 , influencing of the sensor signal P occurs in practice, in effect as an artifact of the pressure measurement, as a result of noises or by body-borne sound which is transmitted to the cylinder pressure sensors. 
         [0082]    Such noises are caused in principle for example by all of the mechanical processes in the valve drive. Among the interference signals thus generated, it is again the case in particular that the dominant ones are those caused by the termination of a valve closing process. In the exemplary embodiment illustrated, for example, the setting-down of the valve plate of the inlet valve  16  on the valve sealing region of the engine block leads to a corresponding (characteristic) interference signal in the cylinder pressure signal P. 
         [0083]    By means of the evaluation of the cylinder pressure signal P, it is thus possible to very accurately detect the time (and/or crank angle) at which the inlet valve  16  closes. 
         [0084]    In principle, and by contrast to the exemplary embodiment illustrated, it is conceivable for use to be made of less than one cylinder pressure sensor per cylinder  12 . In particular because each valve of the internal combustion engine  10  has a different spatial relationship (for example spacing) with respect to a cylinder pressure sensor, it is possible on the basis of predetermined evaluation criteria to realize an assignment of a certain interference signal to a certain valve. It is better, and simpler with regard to evaluation outlay, if, as is also provided in the exemplary embodiment, in each case one cylinder sensor  32  is provided per cylinder (on a wall delimiting the latter, for example in the cylinder head). 
         [0085]    A simplification of the distinction of interference signals caused by the different valves of one and the same cylinder  12  can be realized for example by virtue of the respective cylinder pressure sensor  32  being arranged not “in the middle” between the valves but rather for example with clearly different “acoustic spacings” to the individual valves. In this case, it is the case in particular that the amplitudes of the interference signals will differ according to which of the valves the respective acoustic interference noise originated from. 
         [0086]    By contrast to the exemplary embodiment illustrated in  FIG. 1 , the internal combustion engine  10  could also have only a single cylinder  12 . Such single-cylinder internal combustion engines are often used for example in motorcycles. In the case of a single-cylinder internal combustion engine, too, it is possible by means of the disclosed techniques to realize the attainment of a signal which is expedient for the determination of the switching state of the valve drive adjustment device. 
         [0087]    One possibility for the realization of the evaluation of the cylinder pressure signal P will be explained in more detail below on the basis of  FIGS. 2 and 3 . 
         [0088]      FIG. 2  shows an exemplary profile of a cylinder pressure signal P, measured in the internal combustion engine  10  by means of a cylinder pressure sensor  16 , as a function of the crank (shaft) angle CRA. In this illustration, the value of CRA=0° corresponds to top dead center of the piston movement in the cylinder  12 . The profile of the signal P is illustrated here for the situation of externally driven operation of the internal combustion engine  10 . A similar signal profile is however also obtained in overrun operation. 
         [0089]    Clearly visible in  FIG. 2  is an interference signal S 1  superposed on the actual cylinder pressure profile at a crank angle CRA of approximately −140°, which interference signal, in the example illustrated, can be assigned to the closing of the inlet valve  16 . 
         [0090]    In one embodiment of the evaluation of the cylinder pressure signal P with regard to such interference components, the cylinder pressure signal P is firstly high-pass filtered. 
         [0091]      FIG. 3  shows the result of a high-pass filtering of the cylinder pressure signal P from  FIG. 2 . The high-pass filtered signal PD is composed, as can be seen in  FIG. 3 , virtually exclusively of the interference signals, such that in a subsequent evaluation stage, the individual interference signals can be more easily detected and assigned to the relevant processes in the valve drive. 
         [0092]    In particular after such high-pass filtering, it is possible in a simple manner to carry out an evaluation with regard to those interference signals which have been generated by the inlet valves and/or outlet valves during the actuation thereof. 
         [0093]    As shown in  FIG. 3 , it is thus possible already by means of a simple high-pass filter and the determination of interference pulses (for example on the basis of the exceedance of a predetermined threshold) to determine a “valve closes” signal from the actual cylinder pressure signal P. Alternatively or in addition to a check of the filtered signal with regard to the exceedance of one or more predetermined thresholds, it would for example be possible to carry out a pattern comparison between the actually detected signal pattern and previously stored signal patterns assigned to respective valve drive processes. Such a pattern comparison may however be carried out only for an “interference signal profile” which has previously already been identified as such. As already mentioned, the start of such an interference signal profile may be established for example by detection of a sudden or abnormal change in the cylinder pressure signal P. The signal profile generated subsequently thereto can, for the purpose of identifying the triggering event, be compared with previously stored signal patterns in order to assign the interference to a certain valve drive process. Such an approach, in which a pattern comparison is carried out at most for the interference signal itself and not for a longer-lasting signal profile provides a useful evaluation result particularly quickly. 
         [0094]    In the exemplary embodiment illustrated, said evaluation result thus provides the time and/or crank angle CRA at which the inlet valve  16  closes. 
         [0095]      FIG. 4  shows a detail from the illustration of  FIG. 2 , wherein there are however plotted two profiles P 1  and P 2  of the cylinder pressure signal P which correspond to the two different actuation characteristics of the valve drive adjustment device  21 . 
         [0096]    As can be seen from  FIG. 4 , in the profile P 1  (for large valve lift, cf. lift curve L 16 - 1  in  FIG. 5 ), there is a clearly pronounced interference S 1  at a crank angle CRA 1  of approximately −140° C. From a comparison with  FIG. 5 , it is clear that said interference signal S 1  is evidently caused by the end of the closing process of the inlet valve  16 . 
         [0097]    For the profile P 2  (for small valve lift) likewise shown in  FIG. 4 , there is by contrast a similar interference S 2  at an earlier crank angle CRA 2  of approximately −230°. The interference signal S 2  is less pronounced. As can be seen from a comparison with  FIG. 5 , said interference signal S 2  is caused by the end of the closing process of the inlet valve  16  during the actuation thereof corresponding to the lift curve L 16 - 2 . 
         [0098]    It will be explained below with reference to  FIGS. 4 and 5  how, by means of the software executed in the control unit  24 , the present setting (switching state) of the valve drive adjustment device  21  is inferred from said “valve closes” information. 
         [0099]    In a manner known per se, the present crankshaft angle CRA is determined in the control unit  24  on the basis of the sensor signals CRK and CAM. 
         [0100]    By means of the already-described evaluation of the cylinder pressure signal P with regard to interference signal, it is then possible to determine the crankshaft angle (for example CRA 1 ) at which such interference signals (for example S 1 ) arise. For this purpose, it may be preferable for a high-pass filtered version of the cylinder pressure signal P (cf.  FIG. 3 ) to be taken into consideration. 
         [0101]    On the basis of said crank angle information, that is to say in the illustrated example CRA 1  or CRA 2 , the detected interference can already be uniquely assigned to the currently present switching state (for example corresponding to the lift curve L 16 - 1 ). This may be done for example by means of a comparison of the determined crank angle (CRA 1 ) with possible crank angles of said type (for example CRA 1  and CRA 2 ) stored in the engine control unit  24 . 
         [0102]    Additionally, software executed in the control unit  24  may also take the qualitative difference between the possible interference signals (S 1  and S 2 ) into consideration in such an evaluation and/or for checking the plausibility of the evaluation result. In the example illustrated, the signal S 1  has for example a significantly greater amplitude than the signal S 2 . Such qualitative differences can also be identified by the engine control unit, which can thus determine the present switching state, or a switch which has taken place, of the actuation characteristic. 
         [0103]    In the engine controller, the assignment of the result of the evaluation of the cylinder pressure signal P to one of several possible switching states may be performed very generally by means of a suitable software algorithm and/or through the use of a previously stored characteristic map or the like. 
         [0104]    In the example described, the result of the evaluation of the cylinder pressure signal P is initially the time and/or crank angle (CRA 1 ) at which the inlet valve  16  closes. The time (and/or some other property of the detected interference signal S 1 ) determined in this specific way is fed, as an input variable, to that part of the engine control software, executed in the control unit  24 , which as an output variable outputs a variable in the software which is representative of the switching state of the valve drive adjustment device  21 . Said output variable is thus calculated in the software as a function of the input variable. 
         [0105]    The switching state of the valve drive adjustment device  21  thus determined is then supplied as an input variable to that part of the engine control software which (if appropriate jointly taking into consideration further engine parameters) serves to predefine the injection times and the fuel amounts to be injected. Said injection times and the fuel amounts are dependent on which actuation characteristic (“large valve lift” or “small valve lift”) is presently being used. It is thus possible, by means of the disclosed evaluation of the cylinder pressure signal with regard to the interference signals characteristic of the valve actuation processes, to construct in particular an injection amount predefinition facility wherein a position sensor provided specifically for detecting the present setting of the valve drive adjustment device  21  can be dispensed with and/or (for example aging-induced) deviations of the position sensor signal can be advantageously adapted. 
         [0106]    In summary, in the internal combustion  10 , the sensitivity of the cylinder pressure sensor  32  to interference noises is utilized to initially derive therefrom information regarding the present position of at least one valve and (by means of possible further evaluation in the region of the control unit  24 ) to provide valuable information (for example CRA 1 ) for the determination of the setting of the valve drive adjustment device  21 . 
         [0107]    With the use of times such as “valve closes” which are determined from the cylinder pressure signal P, real physical feedback regarding the position of the valve is provided to the control unit  24  at all times. Said information can thus advantageously be utilized in the determination of the state of the corresponding adjustment system. 
         [0108]    Furthermore, said information can for example be used in order to detect and/or adapt faults and/or deviations of camshaft position sensors (of the variable valve controller). 
         [0109]    Even operation of the engine without a camshaft sensor is possible (by virtue of the result of the cylinder pressure signal P being taken into consideration instead). Furthermore, emergency running of the engine is possible in the event of a defect of the crankshaft sensor and/or of the camshaft sensor. 
         [0110]    If, during the assembly of the engine  10 , the assignment in terms of rotational angle between the camshaft  20  and crankshaft  22  in the basic position is not carried out correctly, for example during an exchange of a camshaft toothed belt in a motor vehicle workshop, the engine controller  24  has false information regarding the position of the camshaft  22 . This would normally have the result that the parameters for the combustion cannot be correctly set by the engine control unit  24 , which can lead to increased emissions, poor engine running, and in the extreme case even to engine damage. A similar problem arises in the event of deviations resulting from production tolerances, aging etc. Such assembly errors and also deviations from the setpoint position or configuration which arise only later during operation can however likewise advantageously be detected and taken into consideration by means of the evaluation of the cylinder pressure signal P.