Abstract:
The present disclosure relates to internal combustion engines. The teachings thereof may be embodied in methods and devices for controlling the combustion processes taking place in the cylinders of an internal combustion engine. A method for controlling a combustion process in an internal combustion engine may include: measuring an actual camshaft position; measuring the actual rail pressure; calculating a phase correction value based on the measured actual rail pressure and a mass of fuel to be injected; calculating corrected actual camshaft positions based on the measured actual camshaft position and the respective phase correction value; calculating a mass of air depending on the determined corrected actual camshaft position; and calculating a fuel injection mass based on the mass of air determined for each cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application of International Application No. PCT/EP2015/068364 filed Aug. 10, 2015, which designates the United States of America, and claims priority to DE Application No. 10 2014 217 560.7 filed Sep. 3, 2014, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to internal combustion engines. The teachings thereof may be embodied in methods and devices for controlling the combustion processes taking place in the cylinders of an internal combustion engine. 
       BACKGROUND 
       [0003]    Fuel injection systems have a plurality of cylinders, in each of which a fuel-air mixture is introduced and ignited. These cylinders have inlet and outlet valves which engage with cams provided on an inlet valve camshaft or an outlet valve camshaft, their opening and closing times being set by a control unit in dependence on the camshaft position signal provided by a camshaft sensor. 
         [0004]    To determine the mass of air required in each case for the fuel-air mixture, it is typical to use the camshaft position signal provided by the camshaft sensor as an actual position signal for all of the cylinders of the fuel injection system. Furthermore, a setpoint phase shift of the inlet valve camshaft is calculated on the basis of the setpoint air mass and the engine speed. The phase shift is then controlled using the camshaft position signal and the setpoint phase shift. 
         [0005]    A method for controlling the quantity of air and/or the fuel-air ratio for individual cylinders of an internal combustion engine is disclosed in DE 10 2005 057 974 A1. In that document, the amplitude and frequency of a signal, which is not cylinder-specific and is influenced by an actuator which is not cylinder-specific, is determined and is used to identify cylinder-specific signal components, and the cylinder-specific signal components are used as the basis for actuating the actuator, which is not cylinder-specific. 
         [0006]    Furthermore, it is already known to drive the high-pressure pump of a fuel injection system using the cams of a camshaft. In such a fuel injection system, if the pressure in the rail and/or the delivery volume of the high-pressure pump increases, then the torque to be provided therefor by the camshaft also increases. This amended torque causes further torsion of the camshaft. In turn, this leads to undesired deviation in the control times of the inlet valves, which is greater the greater the distance of the respective cam from the camshaft sensor. The undesired deviation in the control times in turn affects the quantity of air with which the respective cylinder is filled, and thus also the associated quantity of fuel. 
       SUMMARY 
       [0007]    The teachings of the present disclosure may be embodied in methods and devices for improving the combustion processes taking place in the cylinders of an internal combustion engine, which reduce the undesired influences of pressure changes in the rail and/or of a change in the delivery volume of the high-pressure pump of the internal combustion engine, on the combustion processes taking place in the cylinders. 
         [0008]    Some embodiments may include a method for improving the combustion processes taking place in the cylinders of an internal combustion engine having a camshaft, a high-pressure pump driven by the camshaft, a rail and a control unit. The method may include the following steps: measuring the actual camshaft position using a camshaft sensor, measuring the actual rail pressure using a rail pressure sensor, determining, for each cylinder, a phase correction value in dependence on the measured actual rail pressure and the mass of fuel to be injected, determining, for each cylinder, corrected actual camshaft positions by evaluating the measured actual camshaft position and the respective phase correction value, determining, for each cylinder, a mass of air in dependence on the determined corrected actual camshaft position, and determining, for each cylinder, a fuel injection mass in dependence on the mass of air determined for each cylinder. 
         [0009]    Some embodiments may include: measuring the actual intake pipe pressure using a pressure sensor arranged in the intake pipe of the internal combustion engine, determining, for each cylinder, the opening times and/or closing times of the inlet valves of the cylinders by evaluating the measured actual intake pipe pressure, and adapting the actual camshaft positions corrected on a cylinder-specific basis, and thus also the air masses determined for each cylinder, using the opening times and/or closing times of the inlet valves, determined for each cylinder. 
         [0010]    Some embodiments may include: measuring the actual pressure in the cylinders using a pressure sensor arranged in the respective cylinder, determining, for each cylinder, the opening times and/or closing times of the inlet valves of the cylinders by evaluating the measured actual pressure in the cylinders, and adapting the actual camshaft positions corrected on a cylinder-specific basis, and thus also the air masses determined for each cylinder, using the opening times and/or closing times of the inlet valves, determined for each cylinder. 
         [0011]    Some embodiments may include a device for improving the combustion processes taking place in the cylinders of an internal combustion engine. The device may include: a camshaft, a high-pressure pump driven by the camshaft, a rail and a control unit. The control unit ( 10 ) may perform: receiving output signals from a camshaft sensor, describing the actual camshaft position, receiving the output signals from a rail pressure sensor, describing the actual rail pressure, determining, for each cylinder, a phase correction value in dependence on the measured actual rail pressure and the mass of fuel to be injected, determining, for each cylinder, corrected actual camshaft positions by evaluating the measured actual camshaft position and the respective phase correction value, determining, for each cylinder, a mass of air in dependence on the determined corrected actual camshaft position, and determining, for each cylinder, a fuel injection mass in dependence on the mass of air determined for each cylinder. 
         [0012]    In some embodiments, the control unit ( 10 ) is designed to carry out the following further steps: receiving the output signals, describing the actual intake pipe pressure, of a pressure sensor arranged in the intake pipe of the internal combustion engine, determining, for each cylinder, the opening times and/or closing times of the inlet valves of the cylinders by evaluating the measured actual intake pipe pressure, and adapting the actual camshaft positions corrected on a cylinder-specific basis, and thus also the air masses determined for each cylinder, using the opening times and/or closing times of the inlet valves, determined for each cylinder. 
         [0013]    In some embodiments, the control unit ( 10 ) is designed to carry out the following further steps: receiving the output signals, describing the actual pressure in the cylinders, of the pressure sensors arranged in the cylinders, determining, for each cylinder, the opening times and/or closing times of the inlet valves of the cylinders by evaluating the measured actual pressure in the cylinders, and adapting the actual camshaft positions corrected on a cylinder-specific basis, and thus also the air masses determined for each cylinder, using the opening times and/or closing times of the inlet valves, determined for each cylinder. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    There follows a description of an exemplary embodiment with reference to the figures, in which: 
           [0015]      FIG. 1  is a block diagram of a device for improving the combustion processes taking place in the cylinders of an internal combustion engine according to the teachings of the present disclosure, and 
           [0016]      FIG. 2  is a more detailed illustration of parts of the device shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    In spite of using just one camshaft sensor, the undesired influences, of torsion of the camshaft by means of pressure changes in the rail and/or of a change in the delivery volume of the high-pressure pump, on the combustion processes in the cylinders may be reduced using the teachings of the present disclosure. Methods may include determining, for each cylinder, the mass of air and of fuel, it being ensured that, for each cylinder, a predefined fuel-air ratio is maintained and the number of pollutant particles contained in the exhaust gas being reduced. 
         [0018]    Some methods include determining, for each cylinder, a phase correction value in dependence on the actual rail pressure and the quantity of fuel to be injected, determining, for each cylinder, corrected actual camshaft positions by evaluating the measured camshaft position and the respective phase correction value, determining, for each cylinder, a mass of air in dependence on the determined corrected actual camshaft position, and determining, for each cylinder, a fuel injection mass in dependence on the mass of air determined for each cylinder. 
         [0019]    In some embodiments, the corrected actual camshaft positions, and thus also the determined cylinder-specific air mass, are adapted using the output signal from a pressure sensor which is arranged either in the intake pipe or in the respective cylinder and provides information relating to the actual pressure in the intake pipe or in the respective cylinder. 
         [0020]      FIG. 1  shows a block diagram of a device for improving the combustion processes taking place in the cylinders of an internal combustion engine. The device shown in  FIG. 1  has a fresh air inlet duct  9  in which are contained a fresh air inlet  11 , an air purification device  12 , and an inlet flap  13 . 
         [0021]    The device shown also has an exhaust gas duct  5  connected to the outlet  2   b  of the turbine  2  of an exhaust-gas turbocharger  1 . The exhaust gas duct  5  contains a catalytic converter  17 , a branching point  18  and a silencer  19 . An exhaust gas recirculation duct  6  branches off at the branching point  18 . This duct  6  has an exhaust gas cooler  20  and an exhaust gas recirculation valve  8 . 
         [0022]    The outlet of the exhaust gas recirculation valve  8  is connected to a first inlet  7   a  of a mixer  7 . The outlet of the inlet flap  13  of the fresh air inlet duct  9  is connected to the second inlet  7   b  of the mixer  7 . The outlet  7   c  of the mixer  7  is connected to the inlet  4   a  of a compressor  4  of the exhaust-gas turbocharger. The compressor  4  has a compressor rotor which is secured in rotation with a shaft  3  which is also secured in rotation with a turbine rotor of the turbine  2 . 
         [0023]    The exhaust gases of an internal combustion engine  16  are supplied, in the form of an exhaust gas stream, to the inlet  2   a  of the turbine. This exhaust gas stream drives the turbine rotor. This also rotates the shaft  3  of the exhaust-gas turbocharger  1 . This rotation of the shaft is transmitted to the compressor rotor. The compressor draws in and compresses the fresh air/exhaust gas mixture that is created in the mixer  7  and is supplied to the inlet  4   a  of the compressor. The compressed fresh air/exhaust gas mixture is expelled at the outlet  4   b  of the compressor and is supplied, via a charge air cooler  14  and a throttle flap  15 , to the internal combustion engine  16 . As already explained above, the exhaust gas created in the internal combustion engine is expelled at the inlet  2   a  of the turbine  2 . 
         [0024]    The device shown in  FIG. 1  also has a control unit  10  which contains a processing unit and multiple memory units in which tables and characteristic diagrams are stored. The output signals from a multiplicity of sensors, which supply the control unit with actual values of a multiplicity of parameters, are supplied to the control unit  10  as input signals. These include, inter alia, a sensor which detects actuation of the accelerator pedal. The output signals from this sensor tell the control unit  10  that there is a desire for acceleration. The device includes a sensor which provides the control unit  10  with information relating to the actual intake pipe pressure. This sensor is provided between the throttle flap  15  and the internal combustion engine  16 . Additional sensors provide information relating to the actual pressure in the cylinders of the internal combustion engine  16 . 
         [0025]    The control unit  10  evaluates the output signals from the sensors, the saved tables and the saved characteristic diagrams to calculate control signals which are used to actuate components of the device shown. Inter alia, the control unit  10  calculates control signals s 1  for the exhaust gas recirculation valve  8  and transmits these thereto. These control signals s 1  cause the opening state of the exhaust gas recirculation valve  8  to change, depending on the immediate requirement, in order to supply more or less exhaust gas to the mixer  7 . 
         [0026]    Furthermore, the control unit  10  determines the air mass of the internal combustion engine  16  on an individual cylinder basis, and uses the air mass determined for each cylinder in order to determine a respective associated fuel injection mass. This is explained in greater detail below with reference to  FIG. 2 , which shows a more detailed illustration of parts of the device shown in  FIG. 1 . 
         [0027]    These include a high-pressure pump  21 , a rail  22  connected to fuel injectors  23 ,  24 ,  25  and  26 , a camshaft  27  that bears cams  28 - 36 , inlet valves  37 - 44 , a total of four cylinders  45 - 48  in each of which a piston  49 - 52  can be moved up and down, and a crankshaft  53  that is connected to the pistons by connecting rods  54 - 57 . In addition,  FIG. 2  shows the control unit  10 , already shown in  FIG. 1 , and a camshaft sensor  58 , a camshaft adjuster  59 , a crankshaft sensor  60  and sensors  61  whose output signals are supplied to the control unit  10 . These sensors include, inter alia, a rail pressure sensor, an intake pipe pressure sensor and pressure sensors arranged in the cylinders. 
         [0028]    The high-pressure pump  21  may be engaged to raise the pressure of the supplied fuel, and to forward the high-pressure fuel to the rail  22 . From the rail  22 , the fuel is supplied to the injectors  23 ,  24 ,  25 ,  26  which each inject the fuel into one of the cylinders  45 - 48 . In that context, the control unit  10  controls the quantity of fuel and the injection times in a known manner. The high-pressure pump  21  is driven, via the cams  36 , by the rotating camshaft  27 . An increase in the pressure of the fuel in the rail and/or in the delivery volume of the high-pressure pump  21  causes further torsion of the camshaft. 
         [0029]    This gives rise to a cylinder-specific offset of the camshaft position with respect to the actual camshaft position measured using the camshaft sensor  58 . The further removed the respective cylinder is from the high-pressure pump  21  or from the cams  36  driving the high-pressure pump  21 , the greater this offset. Furthermore, this offset also increases with increasing rail pressure and with increasing fuel volume to be delivered by the high-pressure pump  21 . 
         [0030]    This offset—which differs from cylinder to cylinder—causes the air mass, introduced into the respective cylinders via the respective associated inlet valves, to deviate from the setpoint air mass predefined by the control unit  10 , and as a result the fuel-air ratio introduced into the respective cylinders deviates from the respective predefined fuel-air ratio that is optimized for the combustion process. This leads to undesired deterioration of the combustion processes taking place in the cylinders, and an increased number of pollutant particles contained in the exhaust gas. 
         [0031]    To avoid these drawbacks, cylinder-specific phase correction values δ01, δ02, δ03 and δ04 are determined. These are determined in dependence on the actual rail pressure which is measured by the rail pressure sensor, and on the quantity of fuel to be injected, predetermined by the control unit  10 , for example by using a characteristic diagram. For each individual cylinder, the determined phase correction values are added by the control unit  10  to the actual camshaft position measured by the camshaft sensor  58 . The cylinder-specific corrected actual camshaft positions, determined by this adding step, are used by the control unit  10  to determine, for each cylinder, the air mass for the respective cylinder. 
         [0032]    The air mass determined for each cylinder is then used to determine, for each cylinder, a respective associated fuel injection mass. In order to further improve the cylinder-specific determining of the air mass, the camshaft positions corrected on a cylinder-specific basis are adapted or optimized by measuring the inlet valve closing times and/or the inlet valve opening times using the output signals from an intake pipe pressure sensor provided in the intake pipe, or using the output signals from cylinder pressure sensors provided in the cylinders. This determines a further correction value for each individual cylinder, which value, together with the phase correction values δ01, δ02, δ03, δ04 already mentioned above and the actual camshaft position information provided by the camshaft sensor  58 , is used to determine a further improved value for the cylinder-specific air masses, which are in turn used to determine a corresponding associated optimized fuel injection mass. 
         [0033]    The above-described approach provides, on a cylinder-specific basis, a predefined, desired fuel-air ratio to underpin the combustion processes in the cylinders, and therefore the number of pollutant particles contained in the exhaust gas may be minimized.