Abstract:
A method and device are provided for detecting when a closing point of a hydraulic valve has been reached. The valve has a closing element operated by an electric actuator. A predetermined voltage for closing the valve is applied to the actuator. A profile of a current flowing through the actuator is detected. Based on a first increase in the profile corresponding to the valve being at least partially open, a subsequent decrease in the profile corresponding to the closing element carrying out a movement to close the valve, and a second increase in the profile following said decrease in the profile, a local minimum of the detected current is determined between the decrease and the second increase in the profile. Depending on the local minimum of the detected current, a closing point is then determined which corresponds to a time point of the local minimum of the detected current.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/EP2011/064361 filed Aug. 22, 2011, which designates the United States of America, and claims priority to DE Application No. 10 2010 039 832.2 filed Aug. 26, 2010, the contents of which are hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     This disclosure relates to a method and a device for detecting when a closing point of a hydraulic valve has been reached. 
     BACKGROUND 
     Hydraulic valves are used, in particular, in high pressure pumps for delivering fuel in injection system for internal combustion engines of motor vehicles. 
     Such valves are subject to high stresses, in particular if they are subject to continuous loading as can be the case in high pressure pumps. Since high pressure pumps are subject to pressures of, for example, 2000 bar or more, stringent requirements are made of the valves in such pumps. 
     SUMMARY 
     One embodiment provides a method for detecting when a closing point of a hydraulic valve has been reached, wherein the valve has a closing body which can be activated by an electric actuator in order to close the valve, having the steps: application of a voltage, predefined for the closing of the valve, to the actuator; detecting a profile of a current flowing through the actuator; starting from a first rise in the profile of the detected current which is representative of the fact that the valve is at least partially opened, a subsequent fall in the profile of the detected current which is representative of the fact that the closing body carries out a movement in order to close the valve, and a second rise in the profile of the detected current subsequent to the fall in the profile of the detected current, determining a local minimum of the detected current between the fall and the second rise in the profile of the detected current; and determining a closing point corresponding to a time of the local minimum of the detected current, as a function of the local minimum of the detected current. 
     Another embodiment provides a device for detecting when a closing point of a hydraulic valve has been reached, wherein the valve has a closing body which can be activated by an electric actuator in order to close the valve, wherein the device is designed for: application of a voltage, predefined for the closing of the valve, to the actuator; detecting a profile of a current flowing through the actuator; starting from a first rise in the profile of the detected current which is representative of the fact that the valve is at least partially opened, a subsequent fall in the profile of the detected current which is representative of the fact that the closing body carries out a movement in order to close the valve, and a second rise in the profile of the detected current subsequent to the fall in the profile of the detected current, determining a local minimum of the detected current between the fall and the second rise in the profile of the detected current; and determining a closing point corresponding to a time of the local minimum of the detected current, as a function of the local minimum of the detected current. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments are explained in more detail below with reference to the drawings, in which: 
         FIG. 1  shows a schematic view of an example pump having a valve in a longitudinal section, and 
         FIG. 2  shows a schematic view of an example voltage and current profile of the valve. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure provide a method and a device for detecting when a closing point of a hydraulic valve has been reached, with which precise and cost-effective operation of the valve is made possible. 
     Some embodiments provide a method and a corresponding device for detecting when a closing point of a hydraulic valve has been reached, wherein the valve has a closing body which can be activated by an electric actuator in order to close the valve. A voltage, predefined for the closing of the valve, is applied to the actuator. A profile of a current flowing through the actuator is detected. Starting from a first rise in the profile of the detected current which is representative of the fact that the valve is at least partially opened, a subsequent fall in the profile of the detected current which is representative of the fact that the closing body carries out a movement in order to close the valve, and a second rise in the profile of the detected current subsequent to the fall in the profile of the detected current, a local minimum of the detected current is determined between the fall and the second rise in the profile of the detected current. A closing point corresponding to a time of the local minimum of the detected current is determined, as a function of the local minimum of the detected current. 
     The time of the local minimum of the detected current is representative of the fact that the valve is currently closed. 
     Certain embodiments are based on the realization that during a movement of the closing body energy is extracted from the actuator and the current drops until the closing body comes to rest again when the closing point of the valve has been reached. One possible advantage is that the closing point of the valve can be determined very precisely. External influences such as, for example, the pressure and the temperature of a medium flowing through the valve can be compensated. As a result, high precision of a rate of throughput of fluid through the valve can be achieved and fluctuations in the fluid throughput rate can be kept small. 
       FIG. 1  shows a pump  10  having a pump housing  12 . The pump  10  is embodied, in particular, as a high pressure pump, e.g., as a radial piston pump. A pump piston  14  is movably mounted in the pump housing  12 . A pressure space  16  is located in the pump housing  12 , at one end of the pump piston  14 . In order to be able to fill the pressure space  16  with fluid, the latter has an inflow line  18  in which a valve  20  which is embodied as an inlet valve may be arranged. The valve  20  which is embodied as an inlet valve may be embodied as a digitally switched valve. The valve  20  facilitates the filling of the pressure space  16  and prevents the fluid from flowing back out of the inflow line  18  during filling. The pressure space  16  also has a discharge line  22  in which a further valve  24  which is embodied as an outlet valve is arranged. As a result, fluid can be expelled from the pressure space  16 . 
     The pump  10  also has a drive shaft  26  which is operatively connected to an eccentric ring  28  and can be rotated in the clockwise direction in a rotational direction D. Instead of the eccentric ring  28 , a camshaft can also be used. 
     Alternatively, the pump  10  can also be embodied as a crank drive pump. 
     The valve  20  has a valve housing  30  with a recess. A spring  32 , a closing body  34  and a sealing element  36  are arranged in the valve housing  30 . The spring  32  prestresses the sealing element  36  by means of the closing body  34  by virtue of the fact that said spring  32  is supported on a wall of the recess of the valve housing  30 . The valve  20  also has a sealing seat  38  which is fixedly arranged with respect to the valve housing  30 . 
     The valve  20  also has an actuator  40 . The actuator  40  has, in particular, a solenoid. The closing body  34  can be activated by the actuator  40 . 
     In the text which follows, the method of functioning of the pump  10  and of the valve  20  are to be described: 
     By means of a rotational movement of the drive shaft  26  in the rotational direction D, the pump piston  14  is moved toward the drive shaft  26  by means of the eccentric ring  28  until said pump piston  14  reaches a bottom dead center. In the process, the valve  20  opens owing to the spring force of the spring  32  and a pressure difference upstream and downstream of the valve  20 . The sealing element  36  lifts off from the sealing seat  38 . The pressure space  16  is then filled with fluid. As a result of a further rotational movement of the drive shaft  26  in the rotational direction D, the pump piston  14  is moved away from the drive shaft  26  by the eccentric ring  28  and in the process compresses the fluid located in the pressure space  16 . At a predefined time, a predefined voltage U_ 1  is applied to the actuator  40  (see profile of a voltage U in  FIG. 2 ). As a result of the application of the predefined voltage U_ 1 , an actuator force which counteracts the spring force can act on the closing body  34 . As a result of the movement of the closing body  34  in the direction of the actuator force and the prevailing pressure conditions upstream and downstream of the valve  20 , the sealing element  36  can come to bear against the sealing seat  38 . The valve  20  is then closed hydraulically and a flow of fluid through the valve  20  is prohibited. The fluid compressed into the pressure space  16  can then be expelled completely from the pump  10  via the further valve  24  which is formed as a discharge valve. The pump piston  14  then has reached a top dead center. 
     If the pump  10  is a fuel high pressure pump of an injection system of an internal combustion engine, the fuel to which high pressure is applied can arrive at a fluid accumulator embodied as a high pressure fuel accumulator, referred to as the common rail. 
     In the text which follows, the detection of when a closing point of the valve  20  is reached will be presented in detail, in particular with reference to  FIG. 2 : 
     At first, the predefined voltage U_ 1  is applied to the actuator  40 . The predefined voltage U_ 1  permits the valve  20  to close. A profile of a current flowing through the actuator  40  is detected. Measured values I_AV of the current flowing through the actuator  40  may be detected. 
     In a first section I_ 1  of the profile of the measured values I_AV of the current the current rises. The rise is primarily dependent on the predefined voltage U_ 1  and an electrical resistance of the actuator  40 . The electrical resistance of the actuator  40  is determined by an ohmic part and an inductive part. As soon as the closing body  34  begins a movement at a time T_A, the profile of the measured values I_AV of the current follows a parabolic shape and ultimately drops here again in a second section  12  of the profile of the measured values I_AV of the current. The second section I_ 2  of the profile of the measured values I_AV of the current represents a movement of the closing body  34  to close the valve  20 . The movement of the closing body  34  lasts until the sealing element  36  has impacted against the sealing seat  38  ( FIG. 1 ). In a third section I_ 3  of the profile of the measured values I_AV of the current, a second rise in the current takes place. Between the fall and the second rise in the profile of the measured values I_AV of the current, a local minimum I_MIN of the current is reached at a time T_MIN. The closing body  34  comes to a standstill, in particular at the time T_MIN. The time T-MIN is representative of the fact that the valve  20  is currently closed. The rise in the current in the third section I_ 3  results from the fact that after the closing body  34  has come to a standstill, no further energy for the movement of the actuator  40  is drawn from the magnetic field thereof. 
     The determination of the measured values I_AV of the current flowing through the actuator  40  may be effected by sampling the current in discrete time steps in such a way that the measured values I_AV at the current flowing through the actuator  40  are spaced apart from one another in such a way that they permit a predefined precision level during the determination of the closing point of the hydraulic valve  20 . The time T_MIN of the local minimum I_MIN of the current may be determined by determining the profile of the current gradients of the profile of the measured values I_AV of the current and using this profile to determine the time T_MIN of the local minimum I_MIN of the current. The time T_MIN which is determined in this way can then be stored in a suitable way. 
     The detected time T_MIN of the standstill of the closing body may be assigned to a crankshaft angle of the pump  10  (illustrated here by a crankshaft signal CRK,  FIG. 2 ) and stored together with the latter. As a result, a high level of accuracy of the closing point of the valve  20  can be achieved in a simple way in conjunction with the crankshaft angle of the pump  10 . 
     As a result, a particularly high level of robustness with respect to faults and fluctuations in the high pressure range of the pump  10  can be achieved. The precise detection of the closing point of the valve  20  enables the expenditure on the determination of the characteristic diagrams for the correction of faults of the closing time of the valve  20  to be kept low. The throughput rate of the pump  10  can be kept constant in a very precise way. If the pump  10  is a fuel high pressure pump of an injection system of an internal combustion engine, the pressure in the common rail connected downstream can be kept very constant. As a result, the accuracy of the injection quantity of injection valves which are connected downstream of the common rail can also be very high. This permits very strict requirements on the emission of internal combustion engines to be met.