Abstract:
The invention relates to an internal combustion engine comprising a crankshaft, a camshaft and an adjusting device, which is used to adjust the phase position of the camshaft in relation to the crankshaft. The phase position is determined in accordance with a detected crankshaft angle and a recorded camshaft angle. A filter coefficient of a filter is determined in accordance with the amplitude of an oscillation of the phase position and the modification of said phase position. A filtered phase position of the determined phase position is calculated using the filter.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is the US National Stage of International Application No. PCT/EP2004/052326, filed Sep. 27, 2004 and claims the benefit thereof. The International Application claims the benefits of European Patent applications No. 10347516.8 EP filed Oct. 13, 2003, all of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to a method and device for determining the phase position of a camshaft of an internal combustion engine.  
       BACKGROUND OF THE INVENTION  
       [0003]     A known internal combustion engine has a crankshaft which is driven by the pistons of the cylinders of the internal combustion engine using connecting rods. In addition, a camshaft is provided on which cams are embodied for driving gas inlet and gas exhaust valves of the internal combustion engine. The camshaft is connected to the crankshaft using a connection element and is driven by this element. More stringent legal regulations with regard to the emission of harmful substances in the case of internal combustion engines require effective measures for reducing the emission of harmful substances. Nitrogen oxide emissions (NOX) can be reduced very effectively by recirculation of the exhaust gas in the combustion chambers of the cylinders of the internal combustion engine. By means of the recirculated exhaust gases in the combustion chamber, the peak temperature of the combustion of the air/fuel mixture is lowered, which then reduces the nitrogen oxide emissions.  
         [0004]     An exhaust gas recirculation can be reached very easily in the internal combustion engine by means of a so-called internal exhaust gas recirculation system. In the case of an internal exhaust gas recirculation process, the crankshaft position is set according to the desired exhaust gas recirculation rate, and while doing so, the gas inlet valve releases the inlet to the cylinder and the gas exhaust valve the exhaust to which an exhaust gas port is routed. This crankshaft angle position is often also called the valve overlap.  
         [0005]     From DE 101 08 055 C1 an internal combustion engine with a camshaft for which the phase position can be adjusted to the crankshaft by using a setting mechanism is known. The setting mechanism can be controlled hydraulically.  
         [0006]     Depending on which point in the operation of the internal combustion engine has been reached, very different exhaust gas recirculation rates must be set. This also applies to the different operating modes in the same way as they, for example, occur in internal combustion engines with injection valves which meter out the fuel directly in the combustion chamber of the cylinder. These operating modes are, for example, a layered or a homogenous operation. Therefore, as a result it is a requirement to set the exhaust gas recirculation rates very quickly from high to low and vice versa and at the same time to set the exhaust gas recirculation rates very accurately. DE 101 08 055 C1 discloses that the phase position is determined in accordance with the camshaft angle and the crankshaft angle.  
       SUMMARY OF THE INVENTION  
       [0007]     The object of the invention is to create a method and a device which respectively make possible an accurate detection of the phase position between a camshaft and a crankshaft of an internal combustion engine.  
         [0008]     The object of the invention is achieved by the features of the independent claims.  
         [0009]     Advantageous embodiments of the invention are defined in the subclaims.  
         [0010]     The outstanding features of the invention are a method and a corresponding device for determining the phase position of a camshaft of an internal combustion engine with a crankshaft, a camshaft and a setting mechanism by means of which the phase position of the camshaft can be adjusted in relation to the crankshaft. A phase position is determined in accordance with a detected crankshaft angle and a recorded camshaft angle. A filter coefficient of a filter is determined in accordance with the amplitude of an oscillation of the phase position and the modification of said phase position. A filtered phase position of the determined phase position is calculated using the filter.  
         [0011]     The invention is based on the knowledge that, in particular in the case of internal combustion engines in which the camshaft or camshafts act on a few two-way gas valves, as is the case for example in a V6 internal combustion engine with two camshafts to which the two-way gas valves or only the gas inlet valves of three cylinders are allocated in each case, strong oscillations overlapping the rotations of the camshaft occur on the basis of valve movements of the two-way gas valves. This then leads to an inaccurate detection of the phase position and therefore, in the event of the phase position being regulated, to the regulation quality being reduced especially during steady-state operation of the regulation.  
         [0012]     By filtering the phase position according to the invention, it is possible that by suitably selecting the filter coefficients both a very good dynamic behavior can be guaranteed when a desired phase position is set and the steady-state accuracy improved when the phase position is set in accordance with the amplitude of an oscillation of the phase position and the modification of said phase position.  
         [0013]     In an advantageous embodiment of the invention the filtering is undertaken by means of a non-recursive filter of the first order. This has the advantage that the filtering process is very easy to implement.  
         [0014]     In a further advantageous embodiment of the invention, the modification of the phase position is filtered and the filter coefficient is determined in accordance with the filtered modification of said phase position. This has the advantage that the phase position can be determined both easily and very accurately.  
         [0015]     In a further advantageous embodiment of the invention, the modification of the phase position is filtered in accordance with the rotation and/or an oil temperature. This has the advantage that the rotation and/or the oil temperature are characteristics for the pumping capacity of a hydraulic pump and with that for a possible dynamic behavior of a hydraulically-activated setting mechanism.  
         [0016]     In a further advantageous embodiment of the invention, the amplitude of the oscillation of the phase position is filtered and the filter coefficient is determined in accordance with the filtered amplitude of an oscillation of the phase position. This has the advantage that the phase position can be determined both easily and very accurately.  
         [0017]     In a further advantageous embodiment of the invention, the amplitude is filtered in accordance with the rotation and/or an oil temperature. This has the advantage that the rotation and/or the oil temperature are characteristics for the pumping capacity of a hydraulic pump and thereby for a possible dynamic behavior of a hydraulically-activated setting mechanism.  
         [0018]     In a further advantageous embodiment of the invention, the reducing of the filter coefficient within a predetermined time or within a predetermined crankshaft angle segment is limited to a predetermined threshold value. As a result of this, in the case of a sudden change from an increasing phase position to a decreasing phase position or vice versa it is possible to prevent the filter coefficient being reduced from a high value to a low value for the short-term which then results in a strong filtering of the phase position which is undesirable this type of non-stationary phase position reponse.  
         [0019]     In a further advantageous embodiment of the invention, filtering is undertaken by means of a non-recursive filter of the second order or higher. As a result of this, the phase position can be filtered even more accurately. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     Embodiments of the invention are explained below on the basis of the accompanying drawings and figures. They are as follows:  
         [0021]      FIG. 1  an internal combustion engine with a control unit,  
         [0022]      FIG. 2 a  further view of the parts of the internal combustion engine,  
         [0023]      FIG. 3 a  flow diagram of a program for determining the phase position of a camshaft in relation to the crankshaft of an internal combustion engine according to  FIG. 1  and  FIG. 2 , and  
         [0024]      FIG. 4 a  flow diagram of a program for setting the phase position between the camshaft and the crankshaft. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Elements with the same construction and function are identified in all the Figures by the same reference symbols.  
         [0026]     An internal combustion engine ( FIG. 1 ) includes an inlet tract  1 , an engine block  2 , a cylinder head  3  and an exhaust gas tract  4 . The inlet tract preferably includes a throttle valve  11 , a manifold  12  and an inlet pipe  13  which is routed to a cylinder Z 1  via an inlet port in the engine block. The engine block also includes a crankshaft  21  which is connected to the piston  24  of cylinder Z 1  by means of a connecting rod  25 .  
         [0027]     The cylinder head includes a valve train with an inlet valve  30 , an exhaust valve  31  and valve gears  32 ,  33 . The gas inlet valve  30  and the gas exhaust valve  31  are driven by means of a camshaft  36  (see  FIG. 2 ) on which cams  39  are embodied for driving the gas inlet valve  30  or the gas exhaust valve  31  or, if required, by means of two camshafts in which case one is allocated to the gas inlet valve  30  and one to the gas exhaust valve  31 .  
         [0028]     The drive for the gas inlet valve  30  and/or the gas exhaust valve  3 , apart from by the camshaft  36  preferably includes a setting mechanism  37  which, on the one hand, is connected to the camshaft  36  and, on the other hand, to the crankshaft  21 , e.g. via gear wheels which are connected to one another via a chain. With the setting mechanism  37  it is possible to adjust the phase position between the crankshaft  21  and the camshaft  36 . The arrangement of the gear wheels and the chain form the connection element.  
         [0029]     This is done in the present embodiment by increasing the hydraulic pressure in the high-pressure chambers  37   a  of the setting mechanism  37  or by decreasing the corresponding pressure depending the direction in which the adjustment should is to be made. The possible adjustment range is shown in  FIG. 2  with the arrow  37   b.    
         [0030]     For example, if two camshafts  36  are provided it is only possible to allocate one camshaft  36  to the setting mechanism  37  while the other camshaft is driven directly by means of the connection element of crankshaft  21 . In this case, the valve overlap of the gas inlet valve  30  and the gas exhaust valve  31  can be changed, i.e. the crankshaft angle position, during which both an inlet and an exhaust of the cylinder are released. It is also possible to modify the valve overlap if two separate setting mechanisms  37  are allocated to two camshafts  36 .  
         [0031]     The cylinder head  3  ( FIG. 1 ) also includes both an injection valve  34  and a spark plug  35 . Alternatively, the injection valve can also be arranged in the inlet pipe  13 .  
         [0032]     The exhaust gas tract  4  includes a catalytic converter  40 .  
         [0033]     In addition, a control unit  6  is provided to which sensors have been allocated, said sensors detecting the different measured quantities and in each case determining the measured value of the measured quantity. The control unit  6  determines, in accordance with at least one of the measured quantities, the controlling variables which are then converted into one or more adjusting signals for controlling the final control elements by means of corresponding actuators.  
         [0034]     The sensors are a pedal position indicator  71  which detects the position of an acceleration pedal  7 , an air mass flow meter  14  which detects an air mass flow upstream of the throttle valve  11 , a temperature sensor  15  which detects the inlet air temperature, a pressure sensor  16  which detects the inlet pipe pressure MAP, a crankshaft angle sensor  22  which detects a crankshaft angle CRK to which a rotational speed is allocated N, a further temperature sensor  23  which detects a coolant temperature, a camshaft angle sensor  36   a  which detects the camshaft angle CAM, a further temperature sensor  25  which detects an oil temperature TOIL and an oxygen sensor  41  which detects a residual oxygen content of the exhaust gas. Depending on the embodiment of the invention, there can be any subset of the mentioned sensors or even additional sensors.  
         [0035]     The final control elements are, for example, the throttle valve  11 , the gas inlet and the gas exhaust valves  30 ,  31 , the injection valve  34 , the spark plug  35  and the setting mechanism  37 .  
         [0036]     In addition to the cylinder Z 1 , the internal combustion engine can also have other cylinders Z 2 -Z 4  to which corresponding final control elements are then also allocated.  
         [0037]     A program for determining the phase position PH between the crankshaft  21  and the camshaft  36  is started in a step S 1  ( FIG. 1 ) in which variables are initialized, if required.  
         [0038]     In a step S 2 , the phase position PH is determined in accordance with the crankshaft angle CRK and the camshaft angle CAM. This, for example, takes place by counting the tooth flanks of a crankshaft angle transmitter of the crankshaft angle sensor  22  referred to a reference position on the camshaft  36  and subsequently converting to the phase position PH.  
         [0039]     In a step S 4 , the amplitude AMP of an oscillation of the phase position PH is determined. A letter n in brackets in each case means a value detected or determined in the current calculation cycle of the program. Accordingly, an n-1 in brackets means a value determined or detected in the last calculation cycle of the program.  
         [0040]     The current amplitude AMP(n) of the oscillation of the phase position PH is determined by forming the difference between the current phase position PH(n) and the phase position PH(n- 1 ) determined in the preceding calculation cycle.  
         [0041]     In a step S 6 , a filtered amplitude AMP_FIL(n) is determined by filtering the currently determined amplitude AMP(n) with a filter of the first order. The filter of the first order has a filter coefficient FF 1  which has either been predetermined permanently, but is determined advantageously beforehand in a step S 22  in accordance with the rotational speed N and/or the oil temperature TOIL. This is preferably done by means of a characteristic or a performance graph and indeed by a characteristic or performance graph interpolation. The characteristic or the performance graph is determined by means of corresponding attempts on an engine test bench or by means of simulations.  
         [0042]     In a step S 8 , the current modification DELTA(n) of the phase position PH is determined by forming the difference between the current phase position PH(n) and the preceding phase position PH(n 1 ).  
         [0043]     In a step S 10 , a filtered modification DELTA_FIL(n) is determined by means of a filter of the first order by filtering the current modification DELTA(n). The filter coefficient FF 2  of the second filter can be predetermined permanently, but is preferably determined beforehand in a step S 24  in accordance with the rotational speed N and/or an oil temperature TOIL and indeed also in a step S 22  preferably by means of a characteristic or a performance graph interpolation.  
         [0044]     In a step S 12 , the current filter coefficient FF 3 ( n ) is then determined for another filter and indeed depending on the filtered amplitude AMP_FIL(n) and the filtered modification DELTA_FIL(n) of the phase position PH. This preferably takes place by means of a performance graph interpolation from a performance graph which was determined beforehand by means of corresponding attempts on an engine test bench. The performance graph values are preferably selected in such a way that, in cases, in which the filtered amplitude AMP_FIL(n) of an oscillation of the phase position is more or less the same as the filtered modification DELTA_FIL(n) of the phase position PH, said performance graph values are relatively the same, for example, have the value 0.7. If, on the other hand, the filtered modification DELTA_FIL(n) almost has the value zero and the filtered amplitude AMP_FIL(n) clearly has a value exceeding zero, the performance graph values are preferably selected to be very small and indeed, for example, with values ranging from 0.1 to 0.2.  
         [0045]     In a step S 18 , a filtered current phase position PH_FIL(n) is then determined with the filter coefficients FF 3  by filtering the current phase position PH(n) using a filter of the first order.  
         [0046]     Preferably, after step S 12 , processing is continued in a step S 14  in which a test is performed to determine whether or not the difference of the filter coefficients FF 3 ( n - 1 ) which was determined in the preceding calculation cycle and the currently determined filter coefficient FF 3 ( n ) exceeds a predetermined threshold value SW. If this is not the case, processing is immediately continued in step S 18 .  
         [0047]     On the other hand, if the condition of step S 14  has been met, then in a step S 16 , the difference of the filter coefficients FF 3 ( n - 1 ) and the threshold value SW determined in the preceding calculation cycle is allocated to the current filter coefficients FF 3 ( n ). As a result of this, it is brought about that the filter coefficient FF 3  changes from the one calculation cycle to the next calculation cycle, but not exceeding the predetermined threshold value SW. As a result of this, in the case of a sudden change from an increasing phase position PH to a decreasing phase position PH or vice versa it is possible to prevent that the filter coefficient FF 3  is reduced from a high value to a low value for the short-term which then results in a strong filtering of the phase position PH which is not desired in the case of such an unsteady course of the phase position PH.  
         [0048]     The program holds out for a predetermined waiting period T_W in a step S 20 , before processing is continued again in a step S 2 . Alternatively, the program can also hold out for a predetermined crankshaft angle in a step S 20  before processing is continued again in step S 2 . The reprocessing of steps S 2  to S 18  then conforms to the next calculation cycle.  
         [0049]     Parallel to determining the filtered phase position PH_FIL, a further program is processed in the program according to  FIG. 3  which determines a setting signal S ( FIG. 4 ) for controlling the setting mechanism  37 .  
         [0050]     The program is started in a step S 26  and preferably close to the time that the internal combustion engine is started. An exhaust gas recirculation rate EGR is determined in a step S 28  and indeed in accordance with a required torque TQ_REQ which should be generated by the internal combustion engine and which is preferably determined in accordance with the position of the acceleration pedal and, if required, other torque requirements such as those of an ABS system or an ESP system. The exhaust gas recirculation rate is advantageously also determined in accordance with an operating mode MOD of the internal combustion engine which, for example, can be a layered or a homogenous operation of the internal combustion engine. The exhaust gas recirculation rate EGR can also be determined in accordance with other operating variables of the internal combustion engine.  
         [0051]     In a step S 30 , a desired value PH_SP of the phase position is then determined in accordance with the exhaust gas recirculation rate EGR, the inlet pipe pressure MAP and in accordance with the rotational speed N and, if required, other operating variables.  
         [0052]     In a step S 32 , the adjusting signal S for activating the setting mechanism  37  is then determined in accordance with the desired value PH_SP of the phase position and the filtered phase position PH_FIL(n). This is preferably done by means of a regulator which is embodied as a P, PI or PID regulator.  
         [0053]     The setting mechanism  37  is then activated with the adjusting signal S. After the step S 32 , the program then holds out for the predetermined waiting period T_W in a step S 34 . Alternatively, the program can also hold out in the step S 34  for a predetermined crankshaft angle before processing is continued again in step S 28 .  
         [0054]     It is possible that, by suitably selecting the filter coefficients FF 3 , the control accuracy of the regulator of step S 28  can be improved to a great extent and at the same time a good dynamic behavior and high steady-state control accuracy can be obtained. This leads to the exhaust gas recirculation rate EGR in the cylinder Z 1  being able to be set very quickly and the steady-state accuracy improved, which then decisively contributes to lower nitrogen oxide emissions.