Patent Publication Number: US-10316785-B2

Title: Apparatus and method for controlling flow control valve for high pressure fuel pump

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an apparatus and a method for controlling a flow control valve for a high-pressure fuel pump, and more specifically, to an apparatus and a method for controlling a flow control valve for a high-pressure fuel pump, which compress fuel at high pressure after an engine inhales and compresses air so as to supply the fuel to an injector for directly injecting the fuel into a cylinder. 
     Description of the Related Art 
     To improve fuel efficiency and performance of a gasoline engine, a technology for a gasoline direct injection (GDI) type engine is under development. 
     A usual gasoline engine generates motive power by a process of intake/compression/combustion/explosion/exhaust of an air/fuel mixture, whereas the GDI type engine inhales and compresses only air and then injects fuel, which is similar to a compression ignition system of a diesel engine. 
     Accordingly, the GDI type engine can implement the compression ratio which is high enough to overcome the compression ratio of the usual gasoline engine, thereby maximizing the fuel efficiency. 
     Fuel pressure is a very important factor in the GDI type engine, so a high-pressure fuel pump having high performance is required for the fuel pressure. 
     For example, an applicant of the present invention has disclosed the high-pressure fuel pump for the GDI type engine in several documents such as patent documents 1 and 2 which are denoted below and registered now. 
     Meanwhile, the high-pressure fuel pump for the GDI type engine according to the related art is mounted at an engine cam shaft, thus a pump shaft is rotated according to the rotation of a cam and a piston of the pump is moved by the torque, thereby forming pressure, such that gasoline fuel is supplied to an injector. 
     To this end, a flow control valve, which controls an opening/closing operation of an inlet-side check valve to control a discharging flow rate of the high-pressure fuel pump, is provided in the high-pressure fuel pump for the GDI type engine according to the related art. 
     In general, a solenoid valve operated in an electromagnetic way due to a coil is applied to the flow control valve. 
     The solenoid valve is opened in a state of no-current, and closed by generating a magnetic field for moving the plunger in the straight direction when a predetermined voltage is applied onto the coil. 
     (Patent document 1) Korean Registered Patent No. 10-1171995 (Published on Aug. 8, 2012) 
     (Patent document 2) Korean Registered Patent No. 10-1182130 (Published on Sep. 12, 2012) 
     (Patent document 3) Korean Registered Patent No. 10-1361612 (Published on Feb. 13, 2014) 
     However, the solenoid for operating the flow control valve generates a vibration and a noise due to an impact when the coil provided in the solenoid collides with a stopper provided at the inlet-side check valve upon operation of the high-pressure fuel pump. 
     Particularly, the inlet-side check valve of the solenoid generates a high frequency noise during an operation at a lower speed section where the engine is relatively silent, thus the high-pressure fuel pump according to the related art causes an increase of dissatisfaction to a driver due to the noise. 
     In addition, the high-pressure fuel pump for the GDI type engine according to the related art has a problem in that a spring mount unit provided in the solenoid is formed in an open type and coupled to an outer side of a body of the high-pressure fuel pump, such that the noise upon operation is discharged to an outer side of the high-pressure fuel pump. 
     To solve the problems mentioned as above, an applicant of the present invention has disclosed and registered the technology on the flow control valve for minimizing the noise and the vibration generated upon operation of the solenoid in patent document 3 denoted above. 
     However, there is a limit to remove the vibration and the noise completely upon operation of an actuator even though the configuration of patent document 3 is applied. 
     In addition, the high-pressure fuel pump for the GDI type engine according to the related art has problems in that an amount of a current consumption increases and a failure or damage on components incurs due to heat generated from the coil as a current is continuously supplied to the coil of the solenoid when the flow control valve operates. 
     SUMMARY OF THE INVENTION 
     To solve the problems as mentioned above, the object of the present invention is to provide an apparatus and a method for controlling a flow control valve for a high-pressure fuel pump, for controlling an amount of a current applied to a coil of the flow control valve which is applied to the high-pressure fuel pump. 
     Another object of the present invention is to provide an apparatus and a method for controlling a flow control valve for a high-pressure fuel pump, for attenuating the noise and the vibration upon the operation of the high-pressure fuel pump by reducing the collision speed between a plunger and a core provided in the flow control valve. 
     To achieve the object as mentioned above, the apparatus for controlling a flow control valve for a high-pressure fuel pump according to the present invention includes: a pressure sensor for sensing pressure of fuel filled in a delivery pipe; a control unit for controlling an operation of a flow control valve by controlling a current applied to a coil to attenuate a noise and a vibration caused by collision between the plunger and a core by adjusting an operation speed of a plunger provided in a solenoid upon opening/closing operation of the flow control valve provided in the high-pressure fuel pump based on a target RPM of an engine received from a main control unit of a vehicle and a sensing signal of the pressure sensor; a power switching unit for supplying or blocking driving power supplied to the flow control valve based on a control signal of the control unit; and a current adjustment unit electrically connected or disconnected with the flow control valve by an operation of the power switching unit to reduce a current supplied to the flow control valve when the current adjustment unit is connected with the flow control valve. 
     In addition, to achieve the object as mentioned above, the method of controlling a flow control valve for a high-pressure fuel pump according to the present invention, during a pull-in time of an opening/closing operation cycle of the flow control valve provided in the high-pressure fuel pump, in which a current is supplied to a coil to generate a magnetic field so as to move a plunger provided in a solenoid toward a core to close the flow control valve, a current supplied to the flow control valve is reduced by using a current adjustment unit connected to a rear end of the flow control valve, thereby preventing a noise and a vibration caused by the collision between a plunger and a core. 
     As mentioned above, according to the apparatus and the method for controlling the flow control valve for the high-pressure fuel pump of the present invention, the noise and the vibration caused by the collision between the plunger and the core upon the closing operation of the flow control valve can be attenuated by adjusting an amount of the current applied to the coil of the flow control valve. 
     In other words, according to the present invention, the current applied to the flow control valve is rapidly reduced when reaching a preset-time during the pull-in time, thus the plunger is moved by inertia, so that the noise and the vibration caused by the collision between the plunger and the core can be attenuated. 
     In addition, according to the present invention, suction force is provided to the plunger by re-applying a current to the flow control valve when reaching a preset-time during a drop time, such that a noise and a vibration due to collision between the plunger and a needle guide can be attenuated. 
     Therefore, according to the present invention, the noise and the vibration due to collision between the plunger and the core can be attenuated by reducing an operation speed of the plunger provided in the flow control valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a fuel supply system using an apparatus for controlling a flow control valve for a high-pressure fuel pump according to a preferred embodiment of the present invention. 
         FIG. 2  is a perspective view showing a high-pressure fuel pump applied to a preferred embodiment of the present invention. 
         FIG. 3  is a cross-sectional view of the flow control valve shown in  FIG. 2 . 
         FIG. 4  is a circuit diagram showing an apparatus for controlling a flow control valve for a high-pressure fuel pump according to a preferred embodiment of the present invention. 
         FIG. 5  is a timing diagram exemplifying a control operation of a flow control valve. 
         FIG. 6  is a flow chart describing a method of controlling a flow control valve for a high-pressure fuel pump according to a preferred embodiment of the present invention step by step. 
         FIGS. 7( a ) and 7( b )  are timing diagrams exemplifying a control operation of a flow control valve. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An apparatus and a method for controlling a flow control valve for a high-pressure fuel pump according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
     Hereinafter, for the convenience of explanation, a flow control valve provided in a high-pressure fuel pump for a GDI type engine will be used in the description. 
     However, the present invention is not limited thereto, and it may be applied not only to the GDI type engine but also to various internal combustion engines such as a direct injection type LPG engine capable of directly injecting various kinds of fuel into a combustion chamber by pressurizing the fuel at the high pressure. 
       FIG. 1  is a block diagram showing a fuel supply system using an apparatus for controlling a flow control valve for a high-pressure fuel pump according to a preferred embodiment of the present invention. 
     As shown in  FIG. 1  according to a preferable embodiment of the present invention, the fuel supply system to which the apparatus for controlling a flow control valve for a high-pressure fuel pump is applied may include: a fuel pump  12  for pumping gasoline fuel filled in a fuel tank  11  to supply the fuel to an engine  15 ; a high-pressure fuel pump  20  for pressurizing the fuel supplied from the fuel pump  12  at a preset high pressure; a delivery pipe  13  filled therein with the fuel pressurized at the high pressure; an injector  14  directly injecting the fuel filled in the delivery pipe  13  at the high pressure into each combustion chamber of the engine  15 ; a pressure sensor  16  for sensing the pressure of the fuel filled in the delivery pipe  13 ; and a control unit  17  for controlling operations of the fuel pump  12 , the high-pressure fuel pump  20 , and the injector  14  based on a target RPM of the engine  15 . 
     The apparatus  10  for controlling the flow control valve for the high-pressure fuel pump according to the present invention is not limited to the configuration of the fuel supply system as described above, and the present invention may be modified to further include various components and fuel flow paths such as an air pressure regulator for regulating the preset pressure of the fuel, and a fuel collecting line R or a bypass line for collecting remaining fuel except for the fuel injected to the engine among the fuel supplied to the delivery pipe  13 , to the fuel tank  12 . 
     A pressure sensor  16  is installed at the delivery pipe  13  to sense the pressure of the fuel filled in the delivery pipe  13 , and the control unit  17  may control operations of the fuel pump  12  and the high-pressure fuel pump  20 , based on the fuel pressure sensed at the pressure sensor  16 . 
     The control unit  17  may perform communication with a main control unit (not shown) of a vehicle, and may be prepared as an electronic control unit for controlling the operations of the fuel pump  12 , the high-pressure fuel pump  20 , and the injector  14 . 
     In addition, the control unit  17  may be prepared as an additional control unit connected and communicated with the electronic control unit. 
     The configuration and operation of the control unit  17  will be described in detail as below with reference to  FIG. 4 . 
     Next, the configuration of the high-pressure fuel pump according to a preferred embodiment of the present invention will be described in detail with reference to  FIGS. 2 and 3 . 
       FIG. 2  is a perspective view showing a high-pressure fuel pump applied to a preferred embodiment of the present invention, and  FIG. 3  is a cross-sectional view of the flow control valve shown in  FIG. 2 . 
     In the following description, the term indicating a direction such as “left”, “right”, “front”, “rear”, “upper” and “lower” may indicate a direction based on a state shown in each drawing. 
     As shown in  FIGS. 2 and 3 , the high-pressure fuel pump  20  may include: a body  21  formed at a side surface thereof with inlet-side and outlet-side openings  211  and  212 ; a bracket  23  coupled to a lower part of the body  21  and provided therein with a suction device  22  for generating suction force with respect to the fuel; a damper unit  24  coupled to an upper part of the body  21  to reduce a pulse of sucked fuel; a flow control valve  30  coupled to the inlet-side opening  211  for opening/closing an inlet-side check valve  40  to control a supply flow rate and a discharging pressure of the fuel; and an outlet-side check valve  25  coupled to the outlet-side opening  212 . 
     In addition, the high-pressure fuel pump  20  may further include a roller tappet unit  26  coupled between the body  21  and an engine cam shaft (not shown) to be integrated with the suction device  22  to transfer a movement to the suction device  22  by converting a rotating movement of the cam into a linear reciprocating movement. 
     The suction device  22  may include: a piston  27  moved up and down by the linear reciprocating movement of the roller tappet unit  26 ; a return spring  28  for providing restoring force to the piston  27 ; and a retainer  29  coupled to lower end portions of the return spring  28  and the piston  27 . 
     The flow control valve  30  controls the opening/closing operation of the inlet-side check valve  40  according to an operation of the solenoid  31 , thereby transferring the fuel, which is transferred to the flow control valve  30  via the damper unit  24 , to the outlet-side check valve  25  through the inlet-side check valve  40 . 
     Accordingly, the flow control valve  30  controls the opening/closing operation of the inlet-side check valve  40  according to the operation of the solenoid  31 , thereby controlling the supply flow rate and the discharging pressure of the fuel supplied to the body  21  of the high-pressure fuel pump  20 . 
     As shown in  FIG. 3 , the flow control valve  30  may include: a solenoid  31  for linearly reciprocating the plunger  32  provided in the solenoid  31  by receiving a current; an inlet-side check valve  40  for supplying fuel to an outlet-side check valve  25  while preventing a back flow of the fuel introduced into the inlet-side check valve  40  according to the movement of the plunger  32 ; a needle  33  for opening/closing the inlet-side check valve  40  by linearly reciprocating according to the operation of the solenoid  31 ; a needle guide  34  for guiding the linear reciprocating movement of the needle  33 ; and a spring  35  installed in the solenoid  31  to provide restoring force to the needle  33 . 
     The solenoid  31  may include: a bobbin  37  wound on an outer surface thereof with a coil  36 ; a core  38  installed inside the bobbin  37 ; and a plunger  32  linearly reciprocating by a magnetic field when a current is supplied to the coil  36 . 
     That is, the flow control valve  30  closes the inlet-side check valve  40  by moving the plunger  32  and the needle  33  toward the core  38  by generating the magnetic field when a current is supplied to the coil of the solenoid  31 , and opens the inlet-side check valve  40  by moving the plunger  32  and the needle  33  toward the inlet-side check valve  40  due to the restoring force of the spring  35  when the current is blocked. 
     The inlet-side check valve  40  may include: a body  41  formed in a cylindrical shape opened at an upper surface and having a filling space in the middle thereof filled with the fuel; a valve body  42  for opening/closing a transfer hole which transfers the fuel filled in the filling space to the body  21 ; a stopper coupled to a lower part of the body  41 ; and an elastic spring  44  installed between the stopper  43  and the valve body  42  to provide elasticity to the valve body  42 . 
     Meanwhile, according to the present invention, the apparatus  10  for controlling the flow control valve for the high-pressure fuel pump is not limited to the configuration of the high-pressure fuel pump  20  as described above, and may be applied to various modifications such as a shape and a combining structure of each component provided in the high-pressure fuel pump  20  and a structure of a flow passage formed therein. 
     Back to  FIG. 1 , the control unit  17  may control an operation of the flow control valve  30  by generating a control signal for controlling an amount of a current applied onto the coil  36  of the solenoid  31  according to a pressure sensing signal sensed at the pressure sensor  16 . 
     That is, the control unit  17  may control strength of a magnetic field generated at the coil  36  to control the operating speed of the plunger  32 , thereby adjusting the amount of the current by varying a voltage of supply power applied to the coil  36  of the solenoid  31 , so as to minimize the noise and the vibration caused by the collision between the plunger  32  and the core  38  when the flow control valve  30  is closed. 
     To this end, the control unit  17  may include: a comparison unit  18  for comparing a target RPM received from a main control unit of the vehicle with a sensed pressure of the fuel sensed at the pressure sensor  16 ; and a signal generating unit  19  for generating a control signal to control an operation of the solenoid  31  according to the comparison result of the comparison unit  18 . 
     The signal generating unit  19  may adjust the amount of the current applied to the coil  36  of the solenoid  31  by varying a voltage based on the comparison result of the comparison unit  18 . 
     For example,  FIG. 4  is a circuit diagram showing an apparatus for controlling a flow control valve for a high-pressure fuel pump according to a preferred embodiment of the present invention. 
     As shown in  FIG. 4 , the apparatus  10  for controlling the flow control valve for the high-pressure fuel pump according to a preferred embodiment of the present invention include: a power switching unit  50  for supplying or blocking driving power supplied to the flow control valve  30  of the high-pressure fuel pump  20  based on a control signal of the control unit  17 ; and a current adjustment unit  60  connected to a rear end of the flow control valve  30  to reduce a current supplied to the flow control valve  30 . 
     The power switching unit  50  may include: a first switch M 1  installed on a power supply line PL for applying the driving power VBat to the flow control valve  20  from a battery (not shown) of the vehicle; a second switch M 2  installed between the first switch M 1  and a ground potential line GND; and a third switch M 3  installed between the flow control valve  30  and the ground potential line GND. 
     In  FIG. 4 , the flow control valve  30  may include components of an inductance L 1  and a resistor R 1  of the coil  36  provided at the solenoid  31 , and resistors R 2  and R 3  may be installed between the power supply line PL and the first switch M 1 , and at the rear end of the flow control valve  30 , respectively. 
     The first to third switches M 1  to M 3  may be prepared as various switching elements such as a metal oxide semiconductor electric field effect transistor or an electric field effect transistor. 
     A drain electrode and a source electrode of the first switch M 1  may be connected to the power supply line PL, and the first switch M 1  may open/close the power supply line according to a control signal S 1  of the control unit  17  applied via a gate electrode. 
     A drain electrode and a source electrode of the second switch M 2  may be connected to the power supply line PL and the ground potential line GND, and the second switch M 2  may be opened/closed according to a control signal S 2  of the control unit  17  applied via a gate electrode. 
     A drain electrode and a source electrode of the third switch M 3  may be connected to the flow control valve  30  and the ground potential line GND, and the third switch M 3  may be opened/closed according to a control signal S 3  of the control unit  17  applied via a gate electrode. 
     The current adjustment unit  60  may be prepared as a snubber circuit including first and second diodes D 1  and D 2  connected to the flow control valve  30  and the ground potential line GND in the forward and reverse directions, respectively. 
     At this point, the second diode D 2  may be prepared as a zener diode having a zener effect, in which a current rapidly flows when a reverse voltage equal to or greater than a specific voltage (zener voltage) is applied thereto. 
     Alternatively, the second diode D 2  may be prepared as a transient voltage suppressor (TVS) diode for enabling a current to flow to the ground potential line GND when a voltage equal to or greater than an intrinsic clamping voltage is supplied thereto. 
     Accordingly, when turning off the third switch M 3  while turning on the first switch M 1 , the current adjustment unit  60  may rapidly reduce a current applied to the flow control valve  30  by grounding the current at the ground potential line GND. 
     For example,  FIG. 5  is a timing diagram exemplifying a control operation of the flow control valve. 
       FIG. 5  is a graph showing a current and a voltage applied to the flow control valve  30  and control signals supplied to the first to third switches according to an opening/closing operation cycle of the flow control valve  30 . 
     The opening/closing operation cycle of the flow control valve  30  includes: a pull-in time for increasing an amount of a current supplied to the coil  36  to generate a magnetic field so as to move the plunger  32  toward the core  38  upon a closing operation of the flow control valve  30 ; a hold time for maintaining the closed flow control valve  30  in a closed state; and a drop time for reducing the amount of the current to open the flow control valve  30 . 
     At this point, the pull-in time and the hold time indicate a working time for applying the voltage of the control signal. 
     In the high-pressure fuel pump  20 , a period of the cycle for closing and opening the flow control valve  30  may be changed according to a driving state of the vehicle, especially, an RPM of the engine  15  since the piston  27  prepared in the suction device  22  is pumped in a linear reciprocating motion by receiving the rotating motion of the cam installed at the cam shaft of the engine  15  through the roller tappet unit  26 . 
     The flow control valve  30  may suck the fuel into the filling space therein through the damper unit  24  by opening the inlet-side check valve  40  upon descending operation of the piston  27 , and transfer the fuel filled in the filling space into the body  24  by closing the inlet-side check valve  40  upon ascending operation of the piston  27  while preventing the back flow of the fuel. 
     The signal generating unit  19  generates a control signal having a preset peak voltage value during the pull-in time, and the current applied to the coil  36  increases up to a predetermined peak current value according to a slope defined by a resistance value of the coil  36 . 
     At this point, the peak current value, which is a current value set by an experimental value to promptly close the inlet-side check valve  40 , may be set as a value equal to or smaller than a maximum current value for implementing a maximum operation speed of the inlet-side check valve. 
     In addition, the signal generating unit  19  may generate control signals S 1  and S 2  to turn on the first switch M 1  and turn off the second switch during the peak time. 
     In addition, the signal generating unit  19  may generate a control signal S 3  to turn off the third switch M 3  when reaching a preset first preset-time, after turning on the first switch as well as the third switch. 
     At this point, the first preset-time indicates a time that the plunger  32  moves for predetermined stroke caused by the inertia after starting a movement by the suction force. 
     The first preset-time may be set as a point elapsed for a predetermined time from a starting point of the pull-in time, or set as a point lapsed for the predetermined ratio with respect to the entire pull-in time, for example 70% to 90%. 
     For example, a time applied with a pull-in current may be set as about 0.6 ms to about 1.0 ms. 
     However, the present invention is not limited thereto, and may be modified variously depending on an entire time of the opening/closing operation cycle of the flow control valve according to a driving state of the vehicle. 
     Accordingly, the first switch M 1  and the third switch M 3  are turned on during the pull-in time, and the third switch M 3  is turned off when reaching the first preset-time, thus the current applied to the flow control valve  30  is rapidly decreased by the current adjustment unit  60   
     That is, as shown in  FIG. 5 , a first voltage GDI_ 1  applied to the flow control valve  30  slightly increases after the first preset-time, and 
     a second voltage GDI_ 2  outputted from the flow control valve  30  rapidly increases after the first preset-time and then rapidly decreases by an operation of the current adjustment unit  60 . 
     Therefore, when reaching a preset time upon the closing operation of the flow control valve, the present invention may control the plunger to make contact with the core by minimizing the suction force applied to the plunger and moving the plunger, which is rapidly moved by the suction force, by using the inertia other than the suction force. 
     Accordingly, the present invention may attenuate the noise and the vibration by minimizing an impact between the plunger and the core when the flow control valve is closed. 
     Meanwhile, the present invention may be modified to turn off the first switch M 1  while turning off the third switch M 3  during the pull-in time, to completely block the current applied to the flow control valve. 
     The signal generating unit  19  generates a control signal in the form of PWM signal having a preset duty value during the hold time to minimize the current consumption due to a constant increase of the current applied to the coil  36  and prevent the overheat of the solenoid  31 . 
     At this point, the signal generating unit  19  may generate a control signal to alternately turn on or off the first switch M 1  and the second switch M 2  while maintaining the third switch M 3  to be turned on. 
     Then, the current applied to the coil  36  may be maintained as a hold current value set lower than the peak current value until the closed inlet-side check valve  40  is opened. 
     At this point, the control signal in the form of PWM signal is applied to alternately turn on or off the first and second switches, such that the current applied to the coil  36  may vary around the hold current value. 
     For example, the control signal generated during the hold time may have a duty value of about 15% to about 25%. 
     The variation of the current may be limited within a preset range. 
     Accordingly, the present invention may maintain the current applied to the coil at the hold current value by supplying a current corresponding to a hold current value which is set lower than the peak current valve, when the closing operation of the inlet-side check valve is completed. 
     Accordingly, the present invention may prevent a failure or a damage of components by minimizing the current consumption due to the constant increase of the current applied to the coil and preventing the overheat of the solenoid. 
     The signal generating unit  19  may block the control signal until the drop time and a next closing operation, and completely block the control signal until the inlet-side check valve  40  in a state of closing operation is opened after the current applied to the coil  36  descends. 
     Meanwhile, the signal generating unit  19  may generate a control signal to apply a current to the flow control valve  30  during a preset time in a process that the plunger  32  is moved by elasticity of a spring  35  provided at the flow control valve  35  during the drop time so as to minimize the noise and the vibration caused by the collision between the plunger  32  and the needle guide  34  upon an opening operation of the inlet-side check valve  40 . 
     Specifically, when reaching a second preset-time in a state of turning on the third switch M 3 , the signal generating unit  19  may generate a control signal in the form of PWM signal having a preset duty value to alternately turn on or off the first switch M 1  and the second switch M 2 . 
     At this point, the second preset-time may be set as a time required for rotating the piston  27  of the high-pressure fuel pump  20  at an angle of about 10° to about 20° from a top dead center. 
     In addition, the signal generating unit  19  may set the duty value of the control signal in the form of a PWM signal generated upon the second preset-time to be equal to or smaller than the duty value of the control signal generated during the hold time. 
     Accordingly, the present invention may attenuate the noise and the vibration caused by collision between the plunger and a needle guide by re-applying a current to the flow control valve for a preset time to generate the suction force smaller than that of the pull-in time. 
     Next, a method of controlling a flow control valve for a high-pressure fuel pump according to a preferred embodiment of the present invention will be described in detail with reference to  FIG. 6 . 
       FIG. 6  is a flow chart describing a method of controlling a flow control valve for a high-pressure fuel pump according to a preferred embodiment of the present invention step by step. 
     In step S 10  of  FIG. 6 , when an engine  15  is ignited by manipulating an ignition key (not shown), 
     the piston  27  provided in the high-pressure fuel pump  20  linearly reciprocates by a rotating operation of the cam installed at the cam shaft, such that the high-pressure fuel pump  20  is driven, thereby starting a pumping operation (S 10 ). 
     Then, the control unit  17  receives a target RPM of the engine by performing communication with a main control unit of a vehicle (S 12 ). 
     The control unit  17  calculates an opening/closing time and an opening/closing duration according to the received target RPM and generates a control signal for adjusting an amount of a current applied to the coil  36  of the flow control valve  30  to close the inlet-side check valve  40  when the piston  27  ascends and open the inlet-side check valve  40  when the piston  27  descends. 
     Specifically, the control unit  17  may generate a control signal according to the pull-in time, hold time, and drop time based on the opening/closing operation cycle of the flow control valve  30 . 
     For example,  FIG. 7  is a timing diagram exemplifying a control operation of the flow control valve, and table 1 shows a timing of the control operation as described in  FIG. 7 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Pull-in time 
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Item 
                 Comparing example 
                 Embodiment example 
               
               
                   
                   
               
               
                   
                 M1 
                 ON 
                 ON 
               
               
                   
                 M2 
                 OFF 
                 OFF 
               
               
                   
                 M3 
                 ON 
                 ON →OFF 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 7( a )  and  FIG. 7( b )  show graphs for a voltage, a current, and a vibration applied to the flow control valve  30  according to a comparing example for explaining the present invention and a preferred embodiment of the present invention with respect to the opening/closing operation cycle. 
     According to the comparing example as shown in  FIG. 7( a )  and Table 1, both the first and the third switches M 1  and M 2  are turned on during the pull-in time. 
     The signal generating unit  19  generates control signals S 1  and S 3  to turn on the first switch M 1  and the third switch M 3  during the pull-in time, and then to turn off the third switch M 3  upon reaching the first preset-time (S 16 ). 
     Accordingly, the plunger  32  moves toward the core  38  by the suction force generated from the solenoid  31 , and moves for a preset stroke by inertia when reaching the first preset-time. 
     According to the embodiment of the present invention, as shown  FIGS. 7( a ) and 7( b ) , the third switch M 3  is turned off after the first preset-time, and the current applied to the flow control valve is rapidly decreased by using the current adjustment unit  60 , thus the plunger  32  is moved by the inertia, such that the noise and the vibration caused by the collision between the plunger  32  and the core  38  may be remarkably decreased in comparison with the comparing example. 
     At this point, when reaching the first preset-time, the control unit  17  may turn off the first switch M 1  together with the third switch M 3 , such that the current applied to the flow control valve  30  is completely blocked. 
     In addition, the signal generating unit  19  generates a control signal to alternately turn on or off the first switch M 1  and the second switch M 2  while maintaining the third switch M 3  in an on-state during the hold time (S 18 ). 
     Accordingly, the present invention may minimize the current consumption due to the constant increase of the current applied to the coil  36  and prevent the overheat of the solenoid  31 . 
     In addition, when reaching the second preset-time in a process that the plunger  32  is moved by elasticity of the spring  35  provided in the flow control valve  35  during the drop time, the signal generating unit  19  may minimize the noise and the vibration caused by collision between the plunger  32  and a needle guide  34  by generating a control signal to re-apply a current to the flow control valve  30 . 
     Accordingly, the present invention may minimize the noise and the vibration due to the collision between the plunger and the core by controlling the operation speed of the plunger by adjusting an amount of the current applied to the coil. 
     At this point, the pressure sensor  16  senses pressure of fuel filled in a delivery pipe  13 , and transfers a sensing signal corresponding to the sensed fuel pressure to the control unit  17  (S 22 ). 
     Then, the control unit  17  compares the sensed fuel pressure with fuel pressure corresponding to a target RPM (S 24 ). 
     As a result of the comparison in S 24 , when the sensed fuel pressure is different from the fuel pressure corresponding to the target RPM, the control unit  17  adjusts an opening/closing time and an opening duration of the valve (S 26 ), and proceeds to step S 14  to continuously control the amount of the current applied to the flow control valve  30 . 
     On the contrary, when the sensed fuel pressure is same as the fuel pressure corresponding to the target RPM as a result of the comparison in S 24 , the control unit  17  maintains the opening/closing time and the opening duration of the valve. 
     In step S 28 , the control unit  17  inspects whether an operation of the engine  15  stops by operating the ignition key in an off-state, and controls to repeat steps S 12  to S 28  until the operation of the engine  15  stops. 
     As a result of the inspection in step S 28 , when the engine  15  stops the operation, the control unit  17  suspends and stops the operation of the apparatus  10  of the flow control valve  30 . 
     According to the steps described above, the present invention may attenuate the noise and the vibration caused by the collision between the plunger and the core upon the closing operation of the flow control valve by adjusting the amount of the current applied to the coil of the flow control valve. 
     Particularly, when reaching a preset-time during the pull-in time, the present invention may attenuate the noise and the vibration due to the collision between the plunger and the core by moving the plunger through the inertia by rapidly reducing the current applied to the flow control valve. 
     In addition, when reaching a preset-time during the drop time, the present invention may attenuate the noise and the vibration caused by the collision between the plunger and the needle guide by applying the suction force to the plunger by re-applying the current to the flow control valve. 
     The present invention implemented by the inventor is described in detail according to the above embodiments, however, is not limited to the embodiments and various modifications are available within the scope without departing from the idea of the present invention. 
     In other words, the flow control valve provided in the high-pressure fuel pump for the GDI type engine is described in the above embodiments of the present invention. 
     However, the present invention may be modified to be applicable not only to the GDI type engine but also to various internal combustion engines such as a direct injection type LPG engine capable of directly injecting various fuel (e.g. LPG or CNG) into a combustion chamber by pressurizing the fuel at the high pressure. 
     The present invention may be applied to a technology related to the apparatus and the method for controlling the flow control valve for the high-pressure fuel pump, in which the apparatus and the method attenuate the noise and the vibration caused by collision between the plunger and the core upon closing operation of the flow control valve by adjusting an amount of a current applied to the coil of the flow control valve.