Abstract:
A method is provided for controlling a valve having a spring, a pin, and an actuator for actuating the pin. A current having a specified current profile is applied to the actuator, starting from an initial current value at which the pin is in an initial position in which the pin allows the valve to move between open and closed positions. The current profile includes a section or several consecutive sections, wherein each section defines an initial current value and a final current value, a first time interval having a continuously falling current, and a subsequent second time interval having a continuously rising current. For each section, the final current value is less than the initial current value. After the specified current profile has been passed through, the pin is in a final position in which the pin prevents the valve from moving between open and closed positions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/EP2012/058105 filed May 3, 2012, which designates the United States of America, and claims priority to DE Application No. 10 2011 075 269.2 filed May 4, 2011, the contents of which are hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The invention relates to a method and a device for controlling a valve, e.g., a valve used in a high-pressure pump in an accumulator-type injection system of an internal combustion engine. 
     BACKGROUND 
     Certain internal combustion engines include an accumulator-type injection system having a high-pressure pump for delivering fluid. Such valves are subjected to intense stresses, in particular if they are subjected to continuous loading such as is the case for example in high-pressure pumps. Since high-pressure pumps are subjected to pressures of for example 2000 bar and greater, high demands are placed on the valves in pumps of said type. Noises can occur both during the closing and during the opening of said valves. 
     SUMMARY 
     One embodiment provides a method for controlling a valve which has a spring with a spring force, an actuator with an actuator force that counteracts the spring force, and a pin which is coupled to the spring and which can be actuated by means of the actuator, in which method the actuator has a current applied to it with a predefined profile proceeding from a starting value of the current, at which the pin is in a starting position in which the pin, in the case of a valve which is open in a de-energized state, permits the closure of the valve, and in the case of a valve which is closed in a de-energized state, permits the opening of the valve, wherein the profile of the current is predefined so as to have one section or multiple temporally consecutive sections, wherein each of the sections has in each case a starting value of the current, a final value of the current, a first time interval with a continuously falling current profile and a temporally subsequent second time interval with a continuously rising current profile, and the sections are configured such that, after the respective section is passed through, the final value of the current is lower than the starting value of the current, and after the predefined profile of the current is passed through, the pin is in an end position in which, in the case of a valve which is open in a de-energized state, said pin does not permit the closure of the valve, and in the case of a valve which is closed in a de-energized state, said pin does not permit the opening of the valve. 
     In a further embodiment, the profile of the current in the temporally consecutive sections is of V-shaped configuration. 
     In a further embodiment, the valve is arranged in an injection system of an internal combustion engine, and the profile of the current is determined as a function of characteristic values of the internal combustion engine. 
     Another embodiment provides a device for controlling a valve which has a spring with a spring force, an actuator with an actuator force that counteracts the spring force, and a pin which is coupled to the spring and which can be actuated by means of the actuator, wherein the device is designed such that the actuator has a current applied to it with a predefined profile proceeding from a starting value of the current, at which the pin is in a starting position in which the pin, in the case of a valve which is open in a de-energized state, permits the closure of the valve, and in the case of a valve which is closed in a de-energized state, permits the opening of the valve, wherein the profile of the current is predefined so as to have one section or multiple temporally consecutive sections, wherein each of the sections has in each case a starting value of the current, a final value of the current, a first time interval with a continuously falling current profile and a temporally subsequent second time interval with a continuously rising current profile, and the sections are configured such that, after the respective section is passed through, the final value of the current is lower than the starting value of the current, and after the predefined profile of the current is passed through, the pin is in an end position in which, in the case of a valve which is open in a de-energized state, said pin does not permit the closure of the valve, and in the case of a valve which is closed in a de-energized state, said pin does not permit the opening of the valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments of the invention are explained below with reference to the drawings, in which: 
         FIG. 1  shows a schematic view of a pump with a valve in a longitudinal section, 
         FIG. 2  shows a schematic view of the valve in three operating states, and 
         FIG. 3  shows a schematic view of a current profile and of a profile of the position of the valve pin with respect to time. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiment of the present invention provide a method and a device for controlling a valve, which method and device permit precise and inexpensive operation of the valve. 
     Some embodiments provide a method and a corresponding device for controlling a valve. The valve has a spring with a spring force, an actuator with an actuator force that counteracts the spring force, and a pin which is coupled to the spring and which can be actuated by means of the actuator. The actuator has a current applied to it with a predefined profile proceeding from a starting value of the current, at which the pin is in a starting position in which the pin, in the case of a valve which is open in a de-energized state, permits the closure of the valve, and in the case of a valve which is closed in a de-energized state, permits the opening of the valve. The profile of the current is predefined so as to have one section or multiple temporally consecutive sections, wherein each of the sections has in each case a starting value of the current, a final value of the current, a first time interval with a continuously falling current profile and a temporally subsequent second time interval with a continuously rising current profile, and the sections are configured such that, after the respective section is passed through, the final value of the current is lower than the starting value of the current, and after the predefined profile of the current is passed through, the pin is in an end position in which, in the case of a valve which is open in a de-energized state, said pin does not permit the closure of the valve, and in the case of a valve which is closed in a de-energized state, said pin does not permit the opening of the valve. 
     This has the advantage that, by means of the predefined current profile with the section or the sections with continuously falling current profile and the temporally subsequent continuously rising current profile, the valve can be closed slowly in the case of a valve which is closed in a de-energized state, or can be opened slowly in the case of a valve which is open in a de-energized state, such that the noise generated by the valve can be kept low, and reliable and sufficiently fast closing or opening, respectively, of the valve can nevertheless be achieved. Furthermore, wear of the valve can be kept low. Furthermore, an inexpensive design of the valve is possible. 
     In one embodiment, the profile of the current in each of the temporally consecutive sections is of V-shaped configuration. This has the advantage that the profile of the current has a simple, easily producible form. 
     In a further embodiment, the valve is arranged in an injection system of an internal combustion engine, and the profile of the current is determined as a function of characteristic values of the internal combustion engine. This has the advantage that the valve can be respectively closed or opened quietly under the operating conditions of the internal combustion engine. 
       FIG. 1  shows a pump  10  having a pump housing  12 . The pump  10  is in particular in the form of a high-pressure pump, e.g., a radial piston pump. A pump piston  14  is movably mounted in the pump housing  12 . A pump chamber  16  is situated in the pump housing  12  at one end of the pump piston  14 . To enable the pressure chamber  16  to be filled with fluid, said pressure chamber has an inflow line  18  in which there may be arranged a valve  20  in the form of an inlet valve, e.g., a digitally switchable inlet valve. The valve  20  facilitates the filling of the pressure chamber  16  and, during the filling process, prevents a return flow of the fluid out of the inflow line  18 . The pressure chamber  16  also has an outflow line  22  in which there is arranged a further valve  24  in the form of an outlet valve. Fluid can thereby be discharged from the pressure chamber  16 . 
     The pump  10  also has a drive shaft  26  which is operatively connected to an eccentric ring  28  and which can be rotated clockwise in a direction of rotation D. Instead of the eccentric ring  28 , use may also be made of a camshaft. The pump  10  may alternatively also be designed as a crank-drive pump. 
       FIG. 2  shows an exemplary embodiment of a valve  20  in three operating states. 
     The valve  20  has a valve housing  29  which has a recess  30 . A spring  32 , a pin  34  and a sealing element  36  are arranged in the recess  30 . The spring  32 , by virtue of its being supported on a wall of the recess  30 , preloads the sealing element  36  via the pin  34 . 
     Also situated in the recess  30  is a sealing seat  38  which is arranged fixedly with respect to the valve housing  29  and which has passage recesses  40 . Fluid can flow via the passage recesses  40  when the sealing element  36  is not bearing against the sealing seat  38 . 
     The valve  20  also has an actuator  42 . The actuator  42  may be a magnet coil. The pin  34  is arranged partially within the actuator  42  and can be actuated by the actuator  42 . 
     The mode of operation of the pump  10  and of the valve  20  will be described below: 
     By means of a rotational movement of the drive shaft  26  in the direction of rotation D, the pump piston  14  is moved by means of the eccentric ring  28  toward the drive shaft  26  until said pump piston reaches a bottom dead centre UT (see also  FIG. 3 ). Here, the valve  20  opens owing to a spring force F_ 1  of the spring  32  and the pressure difference upstream and downstream of the valve  20 . The sealing element  36  lifts from the sealing seat  38 . The pressure chamber  16  is now filled with fluid. By means of a further rotational movement of the drive shaft  26  in the direction of rotation 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 situated in the pressure chamber  16 . At a predefined time, the valve  20  is closed by virtue of a current being applied to the actuator  42 , whereby an actuator force F_ 2 , which counteracts the spring force F_ 1 , can act on the pin  34 . Owing to the movement of the pin  34  in the direction of the actuator force F_ 2  and the prevailing pressure conditions upstream and downstream of the valve  20 , the sealing element  36  can abut against the sealing seat  38 , and a fluid flow through the passage recesses  40  is prevented. The fluid that is compressed in the pressure chamber  16  can now, in its entirety, be discharged out of the pump  10  via the further valve  24  in the form of an outlet valve. The pump piston  14  has now reached a top dead centre OT (see also  FIG. 3 ). 
     If the pump  10  is a high-pressure fuel pump of an injection system of an internal combustion engine, the highly pressurized fuel may pass to a fluid accumulator in the form of a high-pressure fuel accumulator, the so-called common rail. 
     Both during the opening and during the closing of the valve  20 , mechanically and hydraulically induced noises can be generated at the valve  20 . The noises generated during the opening of the valve  20  will be described below on the basis of  FIG. 2 . During the opening of the valve, in a first step, the sealing element  36  abuts against the valve housing  29  ( FIG. 2B ), whereby a first noise can be generated. The pin  34  is subsequently moved in the direction of the sealing element  36  by the spring force F_ 1  of the spring  32 . A further noise can be generated if the sealing element  36  and the pin  34  impact against one another ( FIG. 2C ). If the pin  34  and the sealing element  36  are formed together in one piece, the first noise in particular may be very considerable owing to the joint mass of pin  34  and sealing element  36 . 
     The method for controlling the valve  20  will be presented in detail below for a valve which is open in a de-energized state ( FIG. 3 ). It is self-evident that this may be applied correspondingly to a valve which is closed in a de-energized state. For the explanation of the method, it is the intention only to describe the current profile between top dead centre OT and bottom dead centre UT. 
     For an opening of the valve  20 , a control device is configured to apply a current I with a predefined profile to the actuator  42  (top of  FIG. 3 ). The applied current I decreases proceeding from a starting value I_ 0 . At the starting value I_ 0  of the current, the actuator force F_ 2  is greater than the spring force F_ 1 . The pin  34  is thus pushed in the direction of the spring  32 , counter to the spring force F_ 1 , and is situated in a starting position P_ 0  (bottom of  FIG. 3 ). In this state, the valve  20  can be closed ( FIG. 2A ). If the valve  20  is arranged in the pump  10 , the applied current assumes the initial value I_ 0  when the pump piston  14  reaches top dead centre OT. 
     During the further course of operation, the control device applies the current to the actuator  42  such that the profile of the current has one section or multiple temporally consecutive sections, wherein, in each of the sections, the current I initially continuously decreases in a first time interval Δt 1  and continuously increases again in a second time interval Δt 2 . In the first section, the decrease of the current takes place proceeding from the starting value I_ 0 , at which the actuator force F_ 2  is greater than the spring force F_ 1 . The continuous decrease of the current in the first time interval Δt 1  takes place until a predefined value of the current is reached. In the further profile, in the second time interval Δt 2 , the current continuously increases again until it reaches a final value in the section. The final value of the current is lower than the starting value I_ 0  of the current. 
     In the cyclically consecutive sections, the decrease of the current takes place proceeding from the previously attained final value of the current until a predefined value of the current is reached, before then continuously increasing again in the further profile until it reaches a new final value. In the cyclically consecutive sections, the new final value of the current is in each case lower than the preceding final value of the current. In the example shown in  FIG. 3 , the method is illustrated for four cyclically consecutive sections. 
     In the embodiment illustrated here, the predefined profile of the current in the temporally consecutive sections is of V-shaped configuration. The profile of the current may however also have any other desired form with a continuous decrease and a subsequent continuous increase of the current; for example, the profile of the current may also be U-shaped in one or more of the sections. 
     As the illustrated current profile is passed through, at a certain value of the current, the actuator force F_ 2  becomes lower than the spring force F_ 1 , and the pin  34  can move toward the sealing element  36 . In the example shown in  FIG. 3 , the start of the movement of the pin  34  takes place during the second section of the current profile. When the pin  34  has been set in motion, it is possible, by means of the respective increase of the current in the individual sections of the current profile, for a braking force to be exerted on the pin  34 . The movement of the pin  34  toward the sealing element  36  is thus braked. In the example illustrated, the braking movement of the pin  34  takes place substantially in the third section of the current profile (see bottom of  FIG. 3 ; for comparison, the profile of the movement of the pin  34  without braking movement is illustrated by dashed lines). 
     As a result of the braking of the pin  34 , the latter can, in an end position P_F, come into contact with the sealing element  36  softly. The position of the sealing element  36  with respect to the sealing seat  38  can thereby be fixed such that the valve  20  can be held open in an effective manner. As a result of the slow movement of the pin  34  toward the sealing element  36 , the noise of the valve  20  can be kept very low, and reliable and sufficiently fast opening of the valve  20  is nevertheless possible. As a result of the slow movement of the pin  34 , it is furthermore possible for the wear of the valve  20  to be kept low. 
     If the valve  20  is arranged in the pump  10 , the control devices sets the applied current to zero when the pump piston  14  is close to bottom dead centre UT. A delivery of fuel at the start of the delivery phase of the pump  10  can thus be ensured.