Abstract:
The invention relates to an internal combustion engine comprising an inlet tract, leading to the inlet to a cylinder where a gas inlet valve is arranged. A valve drive for the gas inlet valve is provided, by means of which the valve stroke of the gas inlet may be adjusted using an actuator element, which permits differing cams to operate the gas inlet valve. An inductive actuator drive is arranged on the actuator element in which a voltage is induced during a switching process. A first unit is embodied for recognition of whether a switching of the valve stroke has occurred by means of the voltage induced in the inductive actuator drive which is characteristic of the switching process. A second unit is embodied for the control of at least one further actuator body depending on whether a switching of the valve is recognized in the first switching unit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is the US National Stage of International Application No. PCT/EP2005/051171, filed Mar. 15, 2005 and claims the benefit thereof. The International Application claims the benefits of German Patent application No. 10 2004 012 756.5 filed Mar. 15, 2004. All of the applications are incorporated by reference herein in their entirety. 
   FIELD OF THE INVENTION 
   The invention relates to a method and device for controlling an internal combustion engine. 
   BACKGROUND OF THE INVENTION 
   The requirements relating to the output and efficiency of internal combustion engines are become increasingly stringent. At the same time strict legal provisions require emissions to be kept at low levels. Such requirements can be easily satisfied, if the internal combustion engine is fitted with gas exchange valves and corresponding drives for these, with different valve lift characteristics as a function of the working point of the internal combustion engine. This allows throttle losses to be reduced as air is taken in and optionally allows high exhaust gas recirculation rates to be rapidly set. 
   It is known that the valve lift of a gas inlet valve in the internal combustion engine can be adjusted between a low and high valve lift. For example the Porsche 911 Turbo is fitted with a device for adjusting the valve lift of the gas inlet valve and the gas outlet valve. The internal combustion engine of the said vehicle is also provided with a camshaft, on which a cam with a low lift and two further cams with a higher lift are configured for each gas inlet valve. The cam lift is transmitted to the gas inlet valve by means of a transformer unit. The transformer unit is configured as a bucket tappet, comprising a cylinder element and an annular cylinder element disposed concentrically in relation to it. The cam with a low lift acts on the cylinder element, while the cams with the higher lift act on the annular cylinder element. As a function of the position of the bucket tappet, either the low or higher lift is transmitted to the gas inlet valve. During no-load operation of the internal combustion engine, the low cam lift is transmitted to the gas inlet valve. This results in reduced frictional losses due to the small diameter of the cam used in this operating state and the cylinder element and the lower valve lift. 
   A higher charge movement is also achieved. This enables the emissions of the internal combustion engine to be reduced and fuel consumption to be kept low at the same time. The low valve lift is maintained at low and medium load. If the load requirements imposed on the internal combustion engine are high, a switch is made to the higher valve lift. 
   If an intended switch of the valve lift actually fails to take place and this is not identified, it results in an increase in pollutant emissions in the respective cylinder during the combustion process. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to create a method and device for controlling an internal combustion engine, which enable low levels of pollutant emissions to be achieved during operation of the internal combustion engine. 
   The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are characterized in the subclaims. 
   According to a first aspect, the invention is characterized by a device for controlling an internal combustion engine, with an intake pipe, which leads to an inlet of a cylinder, on which a gas inlet valve is disposed. A valve drive for the gas inlet valve is also assigned to the internal combustion engine, by means of which the valve lift of the gas inlet valve can be adjusted by means of an actuator element, by means of which different cams can be made to act on the gas inlet valve. An inductive actuator drive acts on the actuator element, a voltage being induced in said inductive actuator drive during the course of a switching process. The device comprises a first unit, which is configured to identify whether switching of the valve lift has taken place based on the induced voltage in the inductive actuator drive, which is characteristic of the switching process. It also comprises a second unit, which is configured to control at least one further actuator body, as a function of whether switching has been identified in the first unit. 
   According to a further aspect, the invention is characterized by a method for controlling the internal combustion engine, wherein switching of the valve lift is identified based on the induced voltage in the inductive actuator drive, which is characteristic of the switching process, and wherein at least one actuator body is activated as a function of whether switching has been identified. 
   The invention therefore utilizes the knowledge that during the course of a switching process the voltage, which is characteristic of the switching process, is induced in the inductive actuator drive. According to the invention, in addition to its own actual function as a drive unit, the inductive actuator drive is also used as a sensor, thus allowing simple identification of whether a switching process has actually taken place. This identification also takes place so close in time to the actual occurrence or otherwise of the switching process that at least one actuator body can quickly be accessed, for example an injection valve or a spark plug, even before the power lift of the respective cylinder, which directly follows the required switching of the valve lift. 
   According to one advantageous embodiment of the invention, the first unit is configured to verify whether the induced voltage characteristic of the switching process occurs in the inductive actuator drive within a predetermined camshaft angle range. 
   This has the advantage that the verification of whether the characteristic induced voltage occurs only has to take place within a predetermined time window, corresponding to the predetermined camshaft angle range, and less computing outlay is therefore required. It is also possible to identify even more precisely whether the required switching process of the valve lift has actually taken place, as voltage fluctuations that may occur outside the predetermined camshaft angle range cannot be identified erroneously as the characteristic induced voltage. 
   According to a further advantageous embodiment of the invention, the first unit has a measuring unit, which is configured to measure a voltage drop over the inductive actuator drive in relation to a supply potential of the inductive actuator drive. This has the advantage that fluctuations in the supply potential do not influence the quality of measurement of the voltage drop. This is an important advantage with regard to controlling an internal combustion engine, as the supply potential of a voltage supply for a motor vehicle, in which the internal combustion engine can be disposed, is regularly subject to major fluctuations and the characteristic induced voltage in some instances only has a small potential difference of for example 0.7 V. 
   According to a further advantageous embodiment of the invention, the first unit has a conversion unit, which is configured to convert the voltage drop over the inductive actuator drive, as detected by the measuring unit, to a corresponding voltage drop in relation to a reference potential, which can also be referred to as ground potential, of an evaluation unit. This allows simple evaluation of the voltage drop detected by the measuring unit in the evaluation unit. This is particularly advantageous, when the evaluation unit is configured as a microcontroller, the inputs of which are generally related to the reference potential. 
   According to a further advantageous embodiment of the invention, the measuring unit is assigned a resistor, which can be connected by means of a switch parallel to the inductive actuator drive. This means that the voltage drop at the inductive actuator drive can be measured in a particularly simple manner. 
   According to a further advantageous embodiment of the invention, the measuring unit is configured to detect the voltage drop over a number of inductive actuator drives. This has the advantage that the voltage drop over a number of inductive actuator drives can thus be detected in a more economical manner and no multiplexer is required. 
   According to a further advantageous embodiment of the invention, the measuring unit has a buffer for the detected voltage drop. This has the advantage, particularly in respect of a characteristic induced voltage that only occurs for a very short time, that correspondingly detected measured values can also be read into the evaluation unit at a different time. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are described in more detail below with reference to the schematic drawings, in which: 
       FIG. 1  shows an internal combustion engine with a controller, 
       FIG. 2  shows a further view of parts of the internal combustion engine according to 
       FIG. 1 , 
       FIGS. 3   a  and  3   b  show characteristics of a groove of an actuator element plotted over the crankshaft angle, 
       FIG. 4  shows a block circuit diagram of parts of the controller, 
       FIG. 5  shows a flow diagram of a program, operating in an evaluation unit, 
       FIG. 6  shows a flow diagram of a program operating in a second unit and 
       FIG. 7  shows a second block circuit diagram of parts of the controller. 
     Elements with the same structure or function are marked with the same reference characters in all the figures. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An internal combustion engine ( FIG. 1 ) has an intake tract  1 , an engine block  2 , a cylinder head  3  and an exhaust gas tract  4 . The intake tract  1  preferably has a throttle valve  5 , a manifold  6  and an intake pipe  7 , which leads to a cylinder Z 1  via an inlet duct into the engine block  2 . 
   The engine block  2  also has a crankshaft  9 , which is coupled via a connecting rod  10  to a piston  12  of the cylinder Z 1 . 
   The cylinder head  3  has a valve drive with a gas inlet valve  13  and a gas outlet valve  14  and valve drives  15 ,  16  assigned to these. The valve drives  15 ,  16  comprise a camshaft  18 , which is coupled by means of a coupling mechanism  19  to the crankshaft  9 . The phase angle between the crankshaft  9  and the camshaft  18  can be specified beforehand. It can however also be adjustable. 
   An actuator element  20  is coupled mechanically to the camshaft  18 . The actuator element  20  preferably comprises a first cam  21  and a second cam  22 . The first and second cams  21 ,  22  have different cam lifts. They can however also generally have different cam characteristics. 
   An inductive actuator drive  23  can be made to act on the actuator element  20  and thus brings about an adjustment of the actuator element  20  in the axis marked X. The inductive actuator drive has a pin  24 , which can be moved in the direction of the actuator element  20  by corresponding energizing of the inductive actuator drive  23  in the axis marked Y. The actuator element  20  has a groove  25 , into which the pin  24  can be inserted. If the pin  24  is located in the groove  25  during rotation of the camshaft  18 , the actuator element  20  is displaced in an axial direction in relation to the camshaft  18 , i.e. in the direction of the axis marked X. 
   The characteristics of the groove  25  in the direction marked X are shown in relation to the crankshaft angle CRK with reference to  FIG. 3   a . The characteristics of the groove in a radial direction r are shown in relation to the axis marked Y with respect to the crankshaft angle CRK with reference to  FIG. 3   b . The groove only extends in a radial direction r over a sub-area of the periphery of the actuator element  20 . The basic circle of the actuator element  20  is thereby marked r 0 . The groove  25  is thus not configured in a first crankshaft angle range CRK 1 . Its depth decreases in a radial direction in a crankshaft angle range CRK 2  until the groove is finally no longer present. In a third crankshaft angle range CRK 3  the groove  25  has a constant position in the direction marked by the axis X. In a fourth crankshaft angle range CRK 4  the groove has a changing position in relation to the axis X. In the fourth crankshaft angle range CRK a pin  24  engaged in the groove  25  causes a corresponding axial displacement of the actuator element  20  in the direction of the axis X. 
   The cylinder head  3  also has an injection valve  28  and a spark plug  29 . 
   A controller  30  is also provided, to which sensors are assigned, which detect different measured variables and respectively determine the measured value of the measured variable. The controller, which can also be referred to as a device for controlling the internal combustion engine, determines manipulated variables as a function of at least one measured variable, said manipulated variables then being converted to one or more control signals to control actuator bodies. 
   The sensors are a pedal position sensor  38 , which detects the position of an accelerator pedal  39 , an air mass sensor  32 , which detects an air mass flow, a temperature sensor  33 , which detects an intake air temperature, an intake pipe pressure sensor  34 , which detects the intake pipe pressure, a crankshaft angle sensor  35 , which detects a crankshaft angle CRK, to which a speed N is then assigned, a camshaft angle sensor  37 , which detects a camshaft angle NW. Any sub-set of the said sensors or even additional sensors can be present, depending on the embodiment of the invention. 
   The actuator bodies are for example the throttle valve  5  the gas inlet and gas outlet valves  13 ,  14 , the injection valve  28 , the spark plug  29  or even the actuator element  20 . 
   As well as the cylinder Z 1 , the internal combustion engine preferably also has further cylinders Z 2 , Z 3 , Z 4 , to which corresponding sensors and actuator bodies are assigned and which are activated correspondingly. 
   The controller  30  is preferably one assembly unit. It can however also be made up of individual assembly units that are physically separate from each other. The controller  30  comprises a first unit  40 , which is configured to identify whether switching of the valve lift VL has taken place based on an induced voltage at the inductive actuator drive  23 , which is characteristic of the switching process. The controller  30  also comprises a second unit  41 , which is configured to activate at least one actuator body, for example the injection valve  28  and/or the spark plug  29 , as a function of whether switching of the valve lift VL has been identified in the first unit  40 . 
   The first unit  40  comprises a measuring unit  42 , which is configured to measure a voltage drop V over the inductive actuator drive  23  in relation to a supply potential VBAT ( FIG. 4 ) of a voltage supply, preferably an on-board voltage supply system in a motor vehicle. The inductive actuator drive  23  is coupled on the one hand to the supply potential VBAT. On the other hand the inductive actuator drive  23  can be coupled in an electrically conductive manner to the reference potential GND, as a function of the position of a first switch SW 1  and the inductive actuator drive  23  is similarly coupled in an electrically conductive manner to a Zener diode D 1 . A second switch SW 2  is also provided, as a function of whose position the measuring unit  42  can be connected parallel to the inductive actuator drive  23 . 
   To measure the voltage drop V over the inductive actuator drive  23 , the first switch SW 1  is controlled into its open position and the second switch SW 2  is controlled into its closed position. The measuring unit  42  then detects the voltage drop V over the inductive actuator drive  23  and generates a corresponding measurement signal VM at its output, via which it is coupled in an electrically conductive manner to a conversion unit  44 . The measuring unit  42  thus detects the voltage drop V over the inductive actuator drive  23  in relation to the supply potential VBAT. 
   The conversion unit  44  converts the measurement signal VM of the measuring unit  42  into an output signal VE, which is related to the reference potential GND. This can be done for example by means of a current balancing circuit. At the same time the measurement signal VM of the measuring unit  42  is preferably amplified in the conversion unit  44 . The output signal VE of the conversion unit  44  is then an input signal for the evaluation unit  46 . The output signal VE of the conversion unit  44  is preferably fed to an analog/digital converter input of the evaluation unit  46  and converted there from analog to digital. 
   The correspondingly digitized output signal VE of the conversion unit  44  is then further processed in the evaluation unit  46  and then optionally rescaled there into the voltage drop V over the inductive actuator drive  43 . During operation of the internal combustion engine a program is run in the evaluation unit  46 , said program being described in more detail below with reference to the flow diagram in  FIG. 5 . 
   The program is started in a step S 1 , in which variables can optionally be initialized. The start of the program preferably takes place close in time to the starting up of the internal combustion engine. In a step S 2  it is verified whether there is a requirement to switch the valve lift VL from a low valve lift LO to a high valve lift HI or vice-versa. The actual switching process is controlled by a function in the controller  30 , which activates the inductive actuator drive  23  during the first crankshaft angle range CRK 1  by corresponding activation of the switch SW 1 , such that the pin  24  moves into the groove  25 . If the condition of step S 2  is not satisfied, processing continues in a step S 4 , in which the program is halted for a predetermined waiting period T_W, before the condition of step S 2  is verified again. 
   If however the condition of step S 2  is satisfied, it is verified in a step S 6  whether the current camshaft angle NW is greater than a first camshaft angle NW 1  and at the same time smaller than a second camshaft angle NW 2 . Alternatively the presence of a corresponding crankshaft angle CRK can be verified here, taking the current phase angle between the crankshaft  9  and the camshaft  18  into account correspondingly. The first and second camshaft angles NW 1 , NW 2  are selected such that the camshaft angle range in between corresponds roughly to the second crankshaft angle range CRK 2 , in which the depth of the groove  25  decreases to zero. 
   If the condition of step S 6  is not satisfied, processing continues in step S 4 . If however the condition of step S 6  is satisfied, in a step S 8  the current voltage drop V over the inductive actuator drive  23  is read in. This can be done for example by controlling the switch SW 2  into its closed position at this time and at the same time ensuring that the switch SW 1  is in its open position. The measuring unit  42  then generates its measurement signal VM, which in turn is converted in the conversion unit  44  into the output signal VE and then in turn read in in the evaluation unit  46 . Alternatively the measuring unit  42  can however be configured to buffer a measurement signal VM it has detected. The evaluation unit  46  can then detect the output signal VE irrespective of the time of detection of the measurement signal VM. It is however important that the measuring unit  42  detects the measurement signal VM within the camshaft angle range, which is bounded by the first camshaft angle NW 1  and the second camshaft angle NW 2 . 
   It is then verified in a step S 10  whether the voltage drop V over the inductive actuator drive  23  is greater than a predetermined threshold value THR. The predetermined threshold value THR is preferably determined by experiment or simulation, such that when the voltage drop V at the inductive actuator drive  23  exceeds the threshold value THR, this is characteristic of an induced voltage, which is characteristic of the pin  24  being pressed back out of the groove  25  due to the decrease in the depth of the groove  25 . 
   If the condition of step S 10  is not satisfied, processing continues directly in step S 4 . If however the condition of step S 10  is satisfied, in a step S 12  a logical variable LV_VL is assigned a low valve lift LO or a high valve lift HI according to the requirements specified in step S 2  for switching the valve lift VL. Processing then continues in a similar manner in step S 4 . 
   In the second unit  41  during operation of the internal combustion engine a program is processed, which is described in more detail below with reference to  FIG. 6 . The program is started in a step S 20 , in which variables are optionally initialized. In a step S 22  a fuel mass to be injected MFF is determined as a function of an air mass flow MAF into the cylinder Z 1 , an air/fuel ratio in the cylinder Z 1  LAM and as a function of the value of the logical variable LV_VL. A control signal to activate the injection valve  28  is then generated as a function of the fuel mass to be injected MFF. 
   The waiting time T_W in step S 4  of the program, which is processed in the first unit  40 , is preferably selected such that it can be ensured that the logical variable LV_VL is always updated so promptly in step S 112  that the fuel mass to be injected MFF always has the correct values of the actual valve lift for the current operating cycle of the cylinder Z 1  in step S 22  to determine the fuel mass MFF. 
   In a step S 24  an ignition angle ZW is then determined as a function of the speed N, a required torque TQ_RQ, which is to be set by the internal combustion engine, and the value of the logical variable LV_VL. The required torque TQ_RQ is determined as a function of the detected accelerator pedal position and optionally further variables or torque requirements. The program is then halted in a step S 26  for the predetermined waiting time T_W, which can however be different from the waiting time in step S 4 . 
     FIG. 7  shows a further alternative block circuit diagram of parts of the controller  30 . R refers to a resistor, which is preferably designed to be high-resistance and is provided to detect the voltage drop V over the inductive actuator drive by means of the measuring unit  42 . Further inductive actuator drives, for example those assigned to different cylinders Z 2  to Z 4 , can also be connected in an electrically conductive manner at the node points A and B. If corresponding further second switches SW 2  are then provided, the measuring unit  42  can also be used to detect the respective voltage drop over the further inductive actuator drives. 
   The Zener diode D 2  ensures that the measurement signal VM of the measuring unit can be detected very quickly after the first switch SW 1  is opened. 
   With the controller  30  it is thus possible to identify any malfunction of the actuator element  20  and in particular the inductive actuator drive  23  due to an electrical or mechanical defect or incorrectly timed activation in a very simple manner.