Patent Publication Number: US-9404481-B2

Title: High-pressure pump

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a divisional of Ser. No. 13/933,450, filed Jul. 2, 2013, which is based on Japanese Patent Applications No. 2012-150697 filed on Jul. 4, 2012, and No. 2013-063987 filed on Mar. 26, 2013, the disclosures of each of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a high-pressure pump. 
     BACKGROUND 
     A fuel supply system which supplies fuel to an engine is equipped with a high-pressure pump which pressurizes the fuel suctioned from a fuel tank. A high-pressure pump has a plunger which pressurizes the fuel introduced into a pump chamber through a fuel inlet and a fuel supply passage. The pressurized fuel is discharged through a fuel outlet. 
     JP-2001-304068A shows a high-pressure pump having a needle valve fixed to a movable core. The needle valve sits on or moves apart from a valve seat to close or open the fuel supply passage. The needle valve is supported by a needle guide which is arranged between a movable core chamber and the fuel supply passage. The needle guide has a communication hole which fluidly connects the movable core chamber and the fuel supply passage. Thereby, a movable core chamber functions as a damper chamber, so that a noise due to a collision between the needle valve and the valve seat can be reduced. 
     In the above high-pressure pump, as an opening sectional area of the communication hole is made larger, a flow resistance of the fuel flowing through the communication hole becomes smaller and the operation and a movement of the movable core become quicker. 
     Thus, in a suction stroke of the high-pressure pump, after the movable core and the needle valve collide with a stopper by a biasing force of a spring, it is likely that the movable core and the needle valve may bounce toward a fixed core. At this moment, when the movable core and the needle valve are magnetically attracted to the fixed core in a metering stroke, a valve-close time of the needle valve is made earlier, so that a discharging stroke starts earlier than an intended time. Even if an energization start time of a coil is made later, the fuel discharge quantity is increased. It may be difficult to control the fuel discharge quantity with high accuracy. 
     SUMMARY 
     It is an object of the present disclosure to provide a high-pressure pump capable of controlling its fuel discharge quantity with high accuracy. 
     According to a high-pressure pump of the present disclosure, a movable core chamber and a fuel supply passage are defined by a needle guide. The needle guide has a communication hole fluidly connecting the movable core chamber with the fuel supply passage. An opening sectional area of the communication hole is defined so that a fuel discharged amount decreases as an energization start time of the coil is delayed. 
     A fuel flow from the fuel supply passage to the movable core chamber is adjusted according to the opening sectional area of the communication hole, so that an operation of the movable core can be controlled. Thereby, in the suction stroke, it is restricted that the movable core and the needle bounce toward the fixed core after the needle biases the suction valve toward stopper by means of a biasing force of a biasing portion. Therefore, the relationship between the energization start time of the coil and the fuel discharged amount is properly maintained. The fuel discharged amount of the high-pressure pump can be controlled correctly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a cross-sectional view showing a high-pressure pump according to a first embodiment; 
         FIG. 2  is an enlarged view of an essential part of  FIG. 1 ; 
         FIG. 3  is an enlarged view of an essential part of  FIG. 2 ; 
         FIGS. 4A to 4D  are graphs showing analytical data of stress condition of a gap between a movable core and a fixed core; 
         FIG. 5  is a graph showing a relationship between a bubble collapse strength and a final gap amount between the movable core and the fixed core; 
         FIG. 6  is a graph showing a relationship between a cross-sectional area of a communication hole and the bubble collapse strength in the final gap; 
         FIGS. 7A and 7B  are photographs respectively showing a condition of a surface of the movable core; 
         FIG. 8  is a graph showing frequency characteristics of sound generated from a solenoid valve of the first embodiment and a solenoid valve of a comparative example; 
         FIG. 9  is a graph showing a sound pressure level of a time when a solenoid valve is energized, according to a comparative example; 
         FIG. 10  is a graph showing a sound pressure level of a time when a solenoid valve is energized, according to the first embodiment; 
         FIG. 11  is a graph showing frequency characteristics in a collision region of a solenoid valve of the first embodiment and a solenoid valve of a comparative example; 
         FIG. 12  is a graph showing frequency characteristics in an attenuation region of a solenoid valve of the first embodiment and a solenoid valve of a comparative example; 
         FIG. 13  is a graph showing noise frequency characteristics of when the cross-sectional area of the communication hole is varied in the high-pressure pump of the first embodiment. 
         FIG. 14  is a graph showing overall values of 0 to 10 kHz of when the cross-sectional area of the communication hole is varied in the high-pressure pump of the first embodiment. 
         FIG. 15  is a cross-sectional view showing an essential part of a high-pressure pump according to a comparative example; 
         FIG. 16  is a cross-sectional view showing an essential part of a high-pressure pump according to a second embodiment; 
         FIG. 17  is a graph showing a relationship between an energization start time of a solenoid valve and a fuel discharge amount of a high-pressure pump; 
         FIG. 18  is an enlarged view of part XVIII in  FIG. 17 ; 
         FIGS. 19A to 19C  are charts showing a relationship between an inner diameter of a communication hole and a behavior of a needle; and 
         FIG. 20  is a graph showing a relationship between an opening sectional area of a communication hole and a valve-close-response time of a suction valve. 
     
    
    
     DETAILED DESCRIPTION 
     Multiple embodiments will be described with reference to accompanying drawings. 
     First Embodiment 
     Referring to  FIGS. 1 to 14 , a first embodiment will be described. A high-pressure pump  1  is provided to a fuel-supply system which supplies fuel to an internal combustion engine. The fuel pumped up from a fuel tank is pressurized by the high-pressure pump  1 . The pressurized fuel is accumulated in a delivery pipe. Then, the high-pressure fuel accumulated in the delivery pipe is injected into each cylinder of the engine through a fuel injector. 
     (Configuration of High-Pressure Pump and Electromagnetic Valve) 
     As shown in  FIG. 1 , the high pressure pump  1  is provided with a pump body  40 , a plunger  42 , a damper chamber  50 , a solenoid valve  10 , and a discharge valve  60 . The pump body  40  forms a cylinder  41  therein. The cylinder  41  receives the plunger  42  reciprocatably. A spring  46  is arranged between a spring seat  43  and an oil-seal holder  45 . The spring seat  43  is disposed to a tip end of the plunger  42 . The oil-seal holder  45  holds an oil seal  44  on an outer circumference of the plunger  42 . The spring  46  biases the plunger  42  toward a camshaft (not shown) of the engine. The plunger  42  reciprocates in its axial direction according to a cam profile of the camshaft. When the plunger  42  reciprocates, a volume of the pump chamber  47  varies, so that the fuel is introduced into the pump  47  and is pressurized therein. 
     Next, the damper chamber  50  will be described in detail. 
     The pump body  40  has a cylindrical portion  51  protruding opposite to the cylinder  41 . A cover  52  is provided on the cylindrical portion  51  to define the damper chamber  50 . The damper chamber  50  accommodates a pulsation damper  53 , a supporting member  54 , and a wavy spring  55 . The pulsation damper  53  is comprised of two metallic diaphragms in which air of specified pressure is sealed. The pulsation damper  53  reduces fuel pressure pulsation in the damper chamber  50 . 
     The damper chamber  50  communicates with a fuel inlet (not shown) through a fuel passage (not shown). The fuel in a fuel tank (not shown) is supplied to the fuel inlet. The fuel in the fuel tank is introduced into the damper chamber  50  through the fuel inlet. 
     Next, the solenoid valve  10  will be described in detail. 
     As shown in  FIGS. 2 and 3 , the solenoid valve  10  is disposed in a fuel supply passage  48  which connects the pump chamber  47  and the damper chamber  50 . The fuel supply passage  48  is opened or closed by the solenoid valve  10 . The solenoid valve  10  is provided with a fixed core  11 , a movable core  12 , a coil  13 , a second spring  14 , a core housing  15  and a needle guide  16 . 
     The pump body  40  has a small-diameter portion  49  which extends perpendicularly relative to a center line of the cylinder  41 . An opening of the small-diameter portion  49  is covered with the core housing  15 , whereby the fuel supply passage  48  is defined from the damper chamber  50  to a pump chamber  47 . 
     A stopper  17 , a seat member  18 , and a cylinder member  19  are arranged in the fuel supply passage  48  in this order. The stopper  17  is cup-shaped to accommodate a suction valve  20  therein. The suction valve  20  reciprocates in the cup-shaped stopper  17  and the stopper  17  regulates a movement of the suction valve  20  in a valve-open direction. A first spring  21  is provided between the stopper  17  and the suction valve  20 . The first spring  21  biases the suction valve  20  in a valve-closing direction. The stopper  17  has an aperture  22  through which the fuel flows. 
     The seat member  18  has an annular valve seat  23  on which the suction valve  20  can sit. When the suction valve  20  sits on the valve seat  23 , the fuel supply passage  48  is closed. When the suction valve  20  moves apart from the valve seat  23 , the fuel supply passage  48  is opened. The cylinder member  19  is threaded to a female screw  481  formed on an inner wall of the fuel supply passage  48 . Thereby, the stopper  17 , the seat member  18  and the cylinder member  19  are fixed in fuel supply passage  48 . 
     The needle guide  16  is fixed inside of the core housing  15 . The needle guide  16  separates a movable core chamber  24  from the fuel supply passage  48 . The movable core  12  is accommodated in the movable core chamber  24 . The needle guide  16  has a communication hole  25  which fluidly connects the movable core chamber  24  and the fuel supply passage  48 . The communication hole  25  is comprised of a large-diameter hole  251  and a small-diameter hole  252 . The large-diameter hole  251  confronts to the movable core chamber  24 . The small-diameter hole  252  confronts to the fuel supply passage  48 . According to the first embodiment, an inner diameter of the small-diameter hole  252  is 1.2 mm or less. Preferably, the inner diameter is 1.0 mm or less. That is, an opening sectional area of the small-diameter hole  252  is 0.36 πmm 2  or less. Preferably, the opening sectional area is 0.25 πmm 2  or less. The needle guide  16  supports the needle  26  slidably in its axial direction. 
     One end of the needle  26  is connected to the movable core  12  and the other end can be in contact with the suction valve  20 . The needle  26  has an enlarged portion  27  of which outer diameter is larger than that of the other portion. When the needle  26  moves toward the fixed core, the enlarged portion  27  is brought into contact with the needle guide  16 . Moreover, the needle  26  has a flange  28 . A second spring  22  is provided between the flange  28  and the needle guide  16 . The second spring  14  biases the needle  26  with a biasing force which is greater than that of the first spring  21 . That is, the second spring  14  biases the movable core  12  in such a manner as to be apart from the fixed core  11 . 
     The movable core  12  is made from magnetic material and is accommodated in the movable core chamber  24  which is defined in the core housing  15 . The movable core  12  axially reciprocates in the movable core chamber  24 . The movable core  12  has multiple breathing ports  29  which extend in its axial direction. In the first embodiment, an outer diameter of the movable core  12  is 9.7 mm. An outer diameter of the needle  26  is 3.0 mm. It should be noted that the outer diameters of the movable core  12  and the needle  26  are established based on various factors, such as magnetic attraction force or capacity of the high-pressure pump. 
     The fixed core  11  is made from magnetic material. A ring portion  111  is sandwiched between the fixed core  11  and the core housing  15 . When the needle  26  moves toward the fixed core  11  and the enlarged portion  27  is brought into contact with the needle guide  16 , a small space is defined between the fixed core  11  and the movable core  12 . This small space is referred to as a final gap. 
     In first embodiment, when the final gap is defined, a distance between the fixed core  11  and the movable core  12  is 0.08-0.16 mm. That is, when the outer diameter of the movable core  12  is 9.7 mm, the volume of a final gap is 1.8818 πmm 3  to 3.7636 πmm 3 . 
     A connector  30  is provided to the fixed core  11 . The connector  30  is supported by a cylindrical yoke  31 . The yoke  31  is fixed to the core housing  15 . A coil  13  is wound around a bobbin  32 . When the coil  13  is energized through a terminal  33  of the connector  30 , the coil  13  generates a magnetic field. 
     When the coil  13  is not energized, the movable core  12  and the fixed core  11  are apart from each other due to the biasing force of the second spring  14 . The needle  26  moves toward the pump chamber  47  and the needle  38  pushes the suction valve  20 , whereby the suction valve  20  is opened. When the coil  13  is energized, a magnetic flux is generated in the magnetic circuit formed by the fixed core  11 , the movable core  12 , the yoke  31  and the core housing  15 . The movable core  12  is magnetically attracted toward the fixed core  11  against the biasing force of the second spring  14 . Consequently, the needle  26  relieves a pressing force against the suction valve  20 . 
     Then, the discharge valve  60  will be described hereinafter. 
     The discharge valve  60  is comprised of a discharge valve body  61 , a regulation member  62  and a spring  63 . The pump body  40  defines a discharge passage  64  which extends perpendicularly relative to the center axis of the cylinder  41 . The discharge valve body  61  is slidably accommodated in the discharge passage  64 . The discharge valve body  61  sits on the valve seat  65  to close the discharge passage  64  and moves away from the valve seat  65  to open the discharge passage  64 . The regulation member  62  regulates a movement of the discharge valve body  61  toward a fuel outlet port  66 . One end of the spring  63  is engaged with the regulation member  62  and the other end is engaged with the discharge valve body  61 . The spring  63  biases the discharge valve body  61  toward the valve seat. 
     When the fuel pressure in the pump chamber  47  is increased and the discharge valve body  61  receives a force greater than a total of the biasing force of the spring  63  and the fuel pressure downstream of the valve seat  65 , the discharge valve body  61  moves away from the valve seat  65 . The fuel is discharged through the fuel outlet port  66 . 
     Meanwhile, when the fuel pressure in the pump chamber  47  is decreased and the discharge valve body  61  receives a force smaller than the total of the biasing force of the spring  63  and the fuel pressure downstream of the valve seat  65 , the discharge valve body  61  sits on the valve seat  65 . Thereby, a reverse flow of the fuel from the valve seat  65  toward the pump chamber  47  is avoided. 
     (Operation of High-Pressure Pump) 
     An operation of the high-pressure pump  1  will be described hereinafter. In the following description, a time-lag from when the coil  13  is energized until when the movable core  12 , the needle  26  or the suction valve  20  moves is not considered. 
     (1) Suction Stroke 
     When the plunger  42  slides down from a top dead center toward a bottom dead center, the volume of the pump chamber  47  is increased. The discharge valve body  61  sits on the valve seat  65  to close the discharge passage  64 . 
     Meanwhile, the suction valve  20  receives a differential pressure between the pump chamber  47  and the fuel supply passage  48 , whereby the suction valve  20  moves toward the pump chamber  47  against the biasing force of the first spring  21 . The suction valve  20  is opened. At this time, since the coil  13  has been deenergized, the movable core  12  and the needle  26  are moved toward the pump chamber  14  by the biasing force of the second spring  14 . The movable core  12  and the needle  26  bias the suction valve  20  toward the pump chamber  47 . Thus, the suction valve  20  is kept opened. The fuel is suctioned into the pump chamber  47  from the dumper chamber  50  through the fuel supply passage  48 . 
     (2) Metering Stroke 
     When the plunger  42  slides up from the bottom dead center to the top dead center along with a rotation of the cam shaft, the volumetric capacity of the pump chamber  47  is reduced. At this moment, since the coil  13  has been deenergized, the needle  26  and the suction valve  20  are positioned at the open position by a biasing force of the second spring  14 . The fuel supply passage  48  is kept opened. Thus, the fuel in the pump chamber  47  is returned to the dumper chamber  50  through the fuel supply passage  48 . The pressure in the pump chamber  47  does not increase. 
     (3) Pressurization Stroke 
     While the plunger  42  slides up from the bottom dead center to the top dead center, the coil  13  is energized. The coil  13  generates a magnetic field and a magnetic attraction force is generated between the fixed core  11  and the movable core  12 . When the magnetic attraction force becomes greater than a difference between the biasing force of the second spring  14  and the biasing force of the first spring  21 , the movable core  12  and the needle  26  move toward the fixed core  11 . Thereby, a pushing force of the needle  26  to the suction valve  20  is canceled. The first spring  21  and the low-pressure fuel discharged from the pump chamber  47  bias the suction valve  20  toward the valve seat  23 . The suction valve  20  sits on the valve seat  23  to close the fuel supply passage  48 . 
     After the suction valve  20  sits on the valve seat  23 , the fuel pressure in the pump chamber  47  increases while the plunger  42  slides up to the top dead center. When the fuel pressure applied to the discharge valve body  61  in the pump chamber  47  becomes greater than a total of the fuel pressure applied to the discharge valve body  61  in the discharge passage  64  and the biasing force of the spring  63 , the discharge valve body  61  is opened. Thereby, the high-pressure fuel pressurized in the pump chamber  47  is discharged to the fuel outlet port  66  through the discharge passage  64 . 
     It should be noted that the energization of the coil  13  is stopped in the pressurization stroke. Since the fuel pressure applied to the suction valve  20  in the pump chamber  47  is greater than the biasing force of the second spring  14 , the suction valve  20  is kept closed. 
     The high-pressure pump  1  repeats the above strokes (1) to (3) to pressurize and discharge the fuel which the internal combustion engine requires. 
     (Reduction of Erosion) 
     A stress condition in the final gap between the fixed core  11  and the movable core  12  will be explained. The stress condition represents a condition of an end surface of the movable core  12  confronting to the fixed core  11  or an end surface of the fixed core  11  confronting to the movable core  12 . These end surfaces receive stresses of erosion generated by cavitation. As bubble collapse strength of the cavitation is larger, the stress is greater. 
     The bubble collapse strength is expressed by a product of a void fraction and a force which crushes the bubble. The void fraction is a rate of the amount of bubbles relative to the volume of the gap. The bubble crushing force is expressed by fluid acceleration.
 
(Bubble collapse strength)=(Void fraction (%))×(Fluid acceleration (mm/s 2 ))
 
     As a pressure fluctuation is the gap between the fixed core  11  and the movable core  12  becomes larger, the amount of bubbles is more increased. The pressure fluctuation in the gap is expressed by a following formula (1).
 
Δ P =(Δ V/Vo )× E   (1)
 
     ΔP: Pressure fluctuation in the gap 
     ΔV: Absolute value of the variation of the volume of a gap at a time when the movable core moves to the fixed core 
     Vo: Volume of the gap at a time when the movable core is most apart from the fixed core 
     E: Bulk modulus of the liquid flowing into the gap 
     As the pressure fluctuation ΔP becomes larger, the amount of bubbles in the gap is more increased. 
       FIG. 15  shows a comparative example of a high-pressure pump  2 . The high-pressure pump  2  is a “solid gap type” pump in which the fixed core  11  and the movable core  12  are brought into contact with each other when the coil  13  is energized. In the following description about the comparative example of the high-pressure pump  2 , the substantially same parts and the components as those in the first embodiment are indicated with the same reference numeral and the same description will not be reiterated. 
     In the high-pressure pump  2 , the suction valve  20  and the needle  26  are independently provided in the valve body  3 . Unlike the first embodiment, the needle  26  has no enlarged portion. Thus, in the high-pressure pump  2 , when the coil  13  is energized, the fixed core  11  and the movable core  12  are brought into contact with each other. The pressure fluctuation in a portion between the fixed core  11  and the movable core  12  becomes larger. The void fraction is increased and the bubble collapse strength becomes larger. As a result, the stress applied to the end surfaces of the movable core  12  and the fixed core  11  becomes larger. 
     On the other hand, according to the first embodiment, the solenoid valve  10  is an “air gap type” valve in which the movable core  12  is not brought into contact with the fixed core  11 . Thus, the pressure fluctuation between the fixed core  11  and the movable core  12  becomes smaller. The void fraction is reduced and the bubble collapse strength becomes smaller. 
     Referring to analytical data shown in  FIGS. 4A to 4D , the stress condition in the gap between the movable core  12  and the fixed core  11  of the solenoid valve  10  of the first embodiment will be described. 
       FIG. 4A  shows a behavior of the needle  26 . It should be noted that the needle  26  and the movable core  12  moves together according to the first embodiment. After the cam angle passes 270 (deg), the movable core  12  magnetically attracted toward the fixed core  11  and the needle  26  is also attracted toward the fixed core  11 . The enlarged portion  27  and the needle guide  16  are brought into contact with each other when the cam angle is 290 (deg). The needle  26  comes most close to the fixed core  11 . Then, while the cam angle is 310 to 330 (deg), the coil  13  is deenergized, so that the needle  26  slightly moves toward the pump chamber  47 . While the cam angle is 330 to 350 (deg), the suction valve  20  moves apart from the valve seat  23  and the needle  26  moves toward the pump chamber along with the suction valve  20 . 
       FIG. 4B  shows the void fraction in the gap between the movable core  12  and the fixed core  11 . While the cam angle is 290 to 350 (deg) and the needle  26  moves toward the fixed core  11 , the void fraction significantly varies. An increase and a decrease are repeated. 
       FIG. 4C  shows the fluid acceleration of the fuel flowing through the breathing ports  29  of the movable core  12 . When the needle  26  comes most close to the fixed core  11  at the cam angle of 290 (deg), the fluid acceleration becomes large. Also, while the coil  13  is deenergized at the cam angle of 310 to 330 (deg), the fluid acceleration becomes large. 
       FIG. 4D  shows the bubble collapse strength in the gap between the movable core  12  and the fixed core  11 . The bubble collapse strength becomes the largest value when both the void fraction and the fluid acceleration become large at the cam angle of 290 (deg). Also, when both the void fraction and the fluid acceleration become large at the cam angle of 310 to 330 (deg), the bubble collapse strength becomes large. 
     From the above analytical data shown in  FIGS. 4A to 4D , it is apparent that the bubble collapse strength in the gap between the movable core  12  and the fixed core  11  is largest when both of the void fraction and the fluid acceleration became large. 
     Referring to the analytical data shown in  FIG. 5 , a relationship between a final gap amount and the bubble collapse strength in the final gap will be explained. 
     In a case that a target value of the bubble collapse strength is set to 200 or less, the target value can be obtained when the final gap amount is 0.8 mm or more. However, when the final gap amount is 0.16 mm or more, it is likely that the magnetic attraction force between the movable core  12  and the fixed core  13  may be decreased. Therefore, the final gap amount is established at the value of 0.08 to 0.16 mm. When the outer diameter of the movable core  12  is 9.7 mm, the volume of the final gap is 1.8818 πmm 3  to 3.7636 πmm 3 . 
     Referring to the analytical data shown in  FIG. 6 , a relationship between a cross-sectional area of the communication hole  25  and the bubble collapse strength in the final gap will be explained. 
     A solid line “A” in  FIG. 6  shows a case where the movable core  12  has four breathing ports  29 . An inner diameter of each breathing port  29  is 1 mm and a total cross area of the breathing ports  29  is about 3.14 mm 2 . A solid line “B” in  FIG. 6  shows a case where the movable core  12  has six breathing ports  29 . An inner diameter of each breathing port  29  is 1 mm and a total cross area of the breathing ports  29  is about 4.71 mm 2 . 
     In a case that a target value of the bubble collapse strength is established less than 200, the target value can be obtained when a total cross-sectional area of the breathing ports  29  is about 4.71 mm 2 , and a cross-sectional area of the communication hole  25  is 0.36 πmm 2  (about 1.13 mm 2 ) or less. When the cross-sectional area of the communication hole  25  is 0.36 πmm 2 , the needle guide  16  has only one communication hole  25  of which inner diameter is 1.2 mm or less. 
     Meanwhile, when the cross-sectional area of the breathing ports  29  is made larger, the bubble collapse strength became smaller. However, this effect is smaller than a case in which the cross-sectional area of the communication hole  25  is varied. 
       FIGS. 7A and 7B  respectively show the condition of the end surface of the movable core  12  after the high-pressure pump  1  has been driven for a specified time period. 
       FIG. 7A  shows the condition of a case in which the needle guide  16  has one communication hole  25  of which inner diameter is 1.2 mm. 
       FIG. 7B  shows the condition of a case in which the needle guide  16  has three communication holes  25  of which inner diameter is 1.2 mm. 
     This experiment is conducted under the following conditions: 
     Fuel pressure: 20 MPa, 
     Fuel: Gasoline, 
     Cam mountain: Four cam mountains of 4 mm height, 
     Engine speed: 3500 rpm, 
     Discharge amount of High-pressure-pump: Full discharge, 
     Experiment Time: 180 H (3.7×10 8  times), 
     Final gap: 0.1 mm, 
     Breathing port: Six breathing ports (4.71 mm 2 ) 
     According to the above experimental result, it becomes apparent that the erosion at the end surface of the fixed core  11  is more restricted when the cross-sectional area of the communication hole  25  of a needle guide  16  is made smaller. 
     (Reduction of Noise Vibration) 
     A noise vibration of the high-pressure pump will be described, hereinafter. 
       FIG. 8  is a graph showing frequency characteristics of noise generated by the high-pressure pump of the first embodiment and the high-pressure pump of the comparative example. As above-mentioned, the high-pressure pump of the first embodiment is an “air gap type”, and the high-pressure pump of a comparative example is a “solid gap type.” According to the first embodiment, as shown in  FIGS. 8 and 10 to 13 , the high-pressure pump  1  has three communication holes  25  of which inner diameter is 1.2 nm. 
     Meanwhile, the high-pressure pump of the comparative example shown in  FIG. 15  has a solenoid valve. 
     A dashed line “C” in  FIG. 8  shows the frequency characteristics of the noise generated by the high-pressure pump of the first embodiment. A solid line “D” shows the frequency characteristics of the noise generated by the high-pressure pump of the comparative example. 
     In the high-pressure pump of the first embodiment, the noise of which frequency is around 3 to 5 kHz and 7 to 9 kHz is high. 
       FIG. 9  is a graph showing a sound pressure level of suction-valve-closing noise generated when the coil is energized in the high-pressure pump of the comparative example.  FIG. 10  is a graph showing a sound pressure level of suction-valve-closing noise generated when the coil is energized in the high-pressure pump of the first embodiment. The sound pressure level of the comparative example is quickly attenuated as shown by an arrow “E” in  FIG. 9 . Meanwhile, the sound pressure level of the first embodiment is slowly attenuated as shown by an arrow “F” in  FIG. 10 . 
     The frequency characteristics in a collision region (0.010 to 0.012 sec) of  FIGS. 9 and 10  are shown in  FIG. 11 . A dashed line “G” shows the frequency characteristics in the collision region of the first embodiment. A solid line “H” shows the frequency characteristics in the collision region of the comparative example. As a result, there is no significant difference in frequency characteristics in the collision region between the comparative example and the first embodiment. 
     The frequency characteristics in an attenuation region (0.012 to 0.018 sec) of  FIGS. 9 and 10  are shown in  FIG. 12 . A dashed line “I” shows the frequency characteristics in the attenuation region of the first embodiment. A solid line “J” shows the frequency characteristics in the attenuation region of the comparative example. As the result, in the high-pressure pump of the first embodiment, the noise of which frequency is around 3 to 5 kHz and 7 to 9 kHz is high. The deterioration in frequency characteristics of the high-pressure pump of the first embodiment, which is shown in  FIG. 8 , is caused due to a deterioration in frequency characteristics of valve-close noise of the suction valve in the attenuation region (0.012 to 0.018 sec). 
       FIG. 13  is a graph showing noise frequency characteristics of when the cross-sectional area of the communication hole  25  of the needle guide  16  is varied in the high-pressure pump of the first embodiment. A dashed line “K” in  FIG. 13  represents the frequency characteristics of valve-close noise in the attenuation region (0.012 to 0.018 sec) in a case where the needle guide  16  has three communication holes  25  of which inner diameter is 1.2 mm. The dashed line “K” in  FIG. 13  is identical to the dashed line “I” in  FIG. 12 . A solid line “L” in  FIG. 13  represents the frequency characteristics of valve-close noise in the attenuation region (0.012 to 0.018 sec) in a case where the needle guide  16  has only one communication hole  25  of which inner diameter is 1.2 mm. As a result, it becomes apparent that the noise of which frequency is about 3 to 5 kHz and 6 to 9 kHz is reduced in a case that the needle guide  16  has only one communication hole  25  of which inner diameter is 1.2 mm. 
       FIG. 14  is a chart showing overall values of the noise vibration of which frequency is 0 to 10 kHz. The noise vibration is generated when a cross-sectional area of the communication hole  25  is varied in a case that the needle guide  16  has only one communication hole  25 . 
     In a case that a target value of the overall value of noise vibration is set as “T”, the overall value can be made lower than or equal to “T” when the needle guide  16  has only one communication hole  25  of which inner diameter is 1.2 mm. Preferably, when the needle guide  16  has only one communication hole  25  of which inner diameter is 1.0 mm or less, the overall value of the noise vibration can be further decreased. 
     Advantages of the First Embodiment 
     According to the above first embodiment, following functional advantages can be achieved. 
     (1) The opening sectional area of the communication hole  25  is defined in such a manner as to reduce an erosion on an end surface of the movable core  12  or the fixed core  11 . Specifically, the opening sectional area of the communication hole  25  is larger than zero and is less than or equal to 0.36 πmm 2 . That is, the opening sectional area of the communication hole  25  is larger than 0% and less than or equal to 1.69% relative to a cross sectional area which is obtained by subtracting the cross-sectional area of the needle  26  from the cross-sectional area of the movable core  12 . 
     According to the above configuration, a fluid acceleration of the fuel flowing into the movable core chamber  2  through the fuel supply passage  48  and the communication hole  25  is reduced. Therefore, the fluid acceleration of the fuel flowing from the movable core chamber  24  into the gap between the movable core  12  and the fixed core  11  through the breathing ports  29  is reduced. Since the bubble collapse strength in the gap between the movable core  12  and the fixed core  11  becomes smaller, the erosion on the end surfaces of the movable core  12  and the fixed core  11  can be restricted. As a result, the deterioration in magnetic attraction force between the movable core  12  and the fixed core  11  can be restricted. The discharging efficiency of the high-pressure pump  1  can be maintained. 
     (2) In the first embodiment, when the movable core  12  is magnetically attracted toward the fixed core  11 , the enlarged portion  27  and the needle guide  16  are brought into contact with each other and the final gap is defined between the movable core  12  and the fixed core  11 . Thereby, it can be restricted that bubbles in the fuel in the final gap are collapsed. 
     (3) In the first embodiment, the volume of the final gap between the movable core  12  and the fixed core  11  is established in such a manner that the erosion on the end surfaces of the movable core  12  and the fixed core  11  is reduced and the magnetic attraction force between the movable core  12  and the fixed core  11  is maintained. Specifically, when the final gap is defined, a distance between the fixed core  11  and the movable core  12  is 0.08-0.16 mm. When the outer diameter of the movable core  12  is 9.7 mm, the volume of the final gap is 1.8818 πmm 3  to 3.7636 πmm 3 . The outer diameter of the movable core  12  is not limited to the above value. 
     Thus, the erosion on the end surface of the movable core  12  can be restricted. 
     (4) A noise vibration is generated due to a contact between the enlarged portion  27  and the needle guide  16  when the coil  13  intermittently is energized. In the first embodiment, the opening sectional area of the communication hole  25  is defined in such a manner that the noise vibration is reduced. Specifically, the opening sectional area of the communication hole  25  is 0.36 πmm 2  or less. Preferably, the opening sectional area is 0.25 πmm 2  or less. Thereby, the noise of a specified frequency can be reduced. The noise vibration of the solenoid valve  10  can be reduced. 
     (5) In first embodiment, the needle guide  16  has only one communication hole  25  and its inner diameter is 1.2 mm or less, preferably 1.0 mm or less. Thereby, it can be restricted that the erosion occurs on the end surfaces of the fixed core  11  and the movable core  12 . Also, the noise vibration of the solenoid valve  10  can be reduced. 
     (6) In first embodiment, the second spring  14  is arranged between the flange  28  of the needle  26  and the needle guide  16 . 
     As the comparative high-pressure pump  2  shown in  FIG. 15 , in a case that a spring-accommodating chamber  4  is defined between the movable core  12  and the fixed core  11  to accommodate the second spring  14  therein, it is likely that an erosion may occur on an inner wall surface of the spring-accommodating chamber  4 . 
     Meanwhile, according to the first embodiment, the second spring  14  is arranged in the fuel supply passage  48 , whereby it is avoided that an erosion occurs. 
     (7) The communication hole  25  is comprised of the large-diameter hole  251  and a small-diameter hole  252 . 
     Generally, a precision processing is necessary to form a small-diameter hole, which may increase a manufacturing cost. According to the first embodiment, since the communication hole  25  is comprised of the large-diameter hole  251  and the small-diameter hole  252 , a relative length of the small-diameter hole  252  in the communication hole  25  can be made smaller. Thus, the manufacturing cost can be reduced. 
     (8) The large-diameter hole  251  is formed on an end surface confronting to the movable core chamber  24 . The small-diameter hole  252  is formed on the other end surface confronting to the fuel supply passage  48 . Thus, the area of the other end surface on which a valve seat is formed is not reduced excessively, whereby the second spring  14  is certainly brought into contact with the needle guide  16 . Also, it is avoided that the second spring  14  is inclined. 
     Second Embodiment 
     Referring to  FIGS. 16 to 20 , a second embodiment will be described. In the second embodiment, the substantially same parts and the components as those in the first embodiment are indicated with the same reference numeral and the same description will not be reiterated. 
     (Configuration of High-Pressure Pump) 
     A high-pressure pump is an “air gap type” pump as well as the first embodiment. In the air gap type pump, the movable core  12  and the fixed core  11  are not brought into contact with each other. Moreover, an outer diameter of the movable core  12  is 9.57 mm, and an outer diameter of the needle  26  is 3.3 mm. 
     Referring to  FIG. 16 , configurations of the suction valve  20  and the stopper  17  will be explained in detail. 
     The suction valve  20  is provided with a valve body  201  and a first guide portion  202 . The valve body  201  is disk-shaped and is capable of sitting on or being apart from the valve seat  23  of the seat member  18 . The suction valve  20  is brought into contact with a contacting portion  171  of the stopper  17  at its end surface opposite to the valve seat  23 . Accordingly, a movement of the suction valve  20  in a valve-open direction is restricted. 
     The first guide portion  202  is cylindrical-shaped and extends from the valve body  201  in a direction opposite to the valve seat  23 . An outer peripheral surface of the first guide portion  202  is slidably in contact with an inner peripheral surface of the second guide portion  172  of the stopper  17 . The first guide portion  202  of the suction valve  20  is guided by the second guide portion  172  of the stopper  17 , whereby the suction valve  20  certainly sits on or moves away from the valve seat  23 . 
     The stopper  17  has the contacting portion  171 , the second guide portion  172 , a fixed portion  173 , and the aperture  22 . The contacting portion  171  of the stopper  17  is ring-shaped and is brought into contact with an end surface of the valve body  201 . The second guide portion  172  of the stopper  17  is cylindrical-shaped and extends from the contacting portion  171  in a direction opposite to the valve seat  23 . The second guide portion  172  is slidably in contact with an outer peripheral surface of the first guide portion  202 . The fixed portion  173  of the stopper  17  radially outwardly extends from the contacting portion  171  to be fixed on an inner wall of the fuel supply passage  48 . The fixed portion  173  divides the pump chamber  47  into a plunger chamber  121  and a valve seat chamber  122 . 
     The fixed portion  173  of the stopper  17  has multiple apertures  22 . Specifically, twelve apertures  22  are circumferentially arranged in the fixed portion  173  to fluidly connect the plunger chamber  121  and the valve seat chamber  122 . The second guide portion  172  of the stopper  17  has four axial grooves  70  on its inner wall surface. The four axial grooves  70  are circumferentially arranged at a regular interval. The contacting portion  171  of the stopper  17  has four radial grooves  71  circumferentially. The radial grooves  71  fluidly connect the axial grooves  70  and the apertures  22 . 
     A valve chamber  200  accommodating the first spring  21  is defined between the suction valve  20  and the stopper  17 . The pump chamber  47  and the valve chamber  200  communicate with each other through the radial grooves  71 , the axial grooves  70  and a clearance between the first guide portion  202  and the second guide portion  172 . 
     According to the second embodiment, the radial grooves  71  and the axial grooves  70  correspond to “a passage fluidly connecting the valve chamber and the pump chamber”. It should be noted that a total passage sectional area of the four radial grooves  71  is smaller than an area which is obtained by adding the passage sectional area of four axial grooves  70  and the passage sectional area of the clearance between the first guide portion  202  and the second guide portion  172 . 
     Thus, when the suction valve  20  is opened, the flow rate of the fuel flowing between the valve chamber  200  and the pump chamber  47  depends on the passage sectional area of the four radial grooves  71 . In a metering stroke of the high-pressure pump, the fuel flow into the valve chamber  200  is restricted by decreasing the passage sectional area of the radial grooves  71 , whereby an excessive pressure increase in the valve chamber  200  is restricted, so that a self-close limit speed can be made higher. It should be noted that the self-close limit speed represents a rotating speed of a cam shaft of when the suction valve  20  is closed due to a fuel pressure in the valve chamber  200  or a dynamic pressure of the fuel flowing into the fuel supply passage  48  from the pump chamber  47  in the metering stroke of the high-pressure pump. 
     When the suction valve  20  is closed, the end surface of the valve body  201  is apart from the contacting portion  171  of the stopper  17 . The flow rate of the fuel flowing into the pump chamber  47  from the valve chamber  200  depends on a total area of the passage sectional area of four axial grooves  70  and the passage sectional area of the clearance between the first guide portion  202  and the second guide portion  172 . Thus, by increasing the passage sectional area of four axial grooves  70 , the fuel flows into the pump chamber  47  from the valve chamber  200  in a suction stroke of the high-pressure pump. A suction efficiency of the fuel can be enhanced without a situation where the fuel in the valve chamber  200  becomes fluid resistance. That is, since the suction efficiency of the high-pressure pump in the second embodiment is higher than that in the first embodiment, a fuel discharged amount can be increased. 
     (Opening Sectional Area of Communication Hole) 
     The opening sectional area of the communication hole  25  will be explained hereinafter. 
     In the high-pressure pump of the second embodiment, the opening sectional area of the communication hole  25  is defined in such a manner that a relationship between an energization period of the coil  13  and the fuel discharged amount is maintained. 
       FIG. 17  is a graph showing the relationship between the energization period of the coil  13  and the fuel discharged amount while an inner diameter of the communication hole  25  is varied. In the following descriptions, the inner diameter of the communication hole  25  represents an inner diameter of the small-diameter hole  252 . 
     In  FIG. 17 , a dashed line “S” shows a case where the inner diameter of the communication hole  25  is 0.4 mm, a solid line “T” shows a case where the inner diameter of the communication hole  25  is 0.5 mm, a long dashed short dashed line “U” shows a case where the inner diameter of the communication hole  25  is 0.6 mm, and an two-dot chain line “V” shows a case where the inner diameter of the communication hole  25  is 0.9 mm. 
     Generally, in a high-pressure pump, when a force with which the needle  26  pushes the suction valve  26  is canceled in a metering stroke, the suction valve  20  sits on the valve seat  23  to start the discharging stroke. Thus, as the energization start time of the coil  13  is delayed, the discharge stroke start time is more delayed so that the fuel discharged amount is decreased. It is preferable that such a relationship is maintained in order to control the fuel discharged amount of the high-pressure pump. 
     However, in the cases indicated by the long dashed short dashed line “U” and the two-dot chain line “V”, during an energization period of the coil  13  from BTDC θ 1  to BTDC θ 2 , as the energization start time of the coil  13  is delayed, the fuel discharged amount is more increased. 
     Meanwhile, in the cases indicated by the dashed line “S” and the solid line “T”, as the energization start time of the coil  13  is delayed, the fuel discharged amount is more decreased. 
       FIG. 18  is an enlarged view of XVIII portion in  FIG. 17 .  FIG. 18  shows only cases indicated by the two-dot chain line “V” and the dashed line “S”. 
     During an energization period of the coil  13  from BTDC  70  to BTDC θ 1 , in both cases indicated by lines “V” and “S”, as the energization start time of the coil  13  is delayed, the fuel discharged amount is more decreased. 
     During an energization period of the coil  13  from BTDC θ 1  to BTDC θ 2 , in the case indicated by line “V”, as the energization start time of the coil  13  is delayed, the fuel discharged amount is not decreased. The reason of the above will be explained with reference to  FIGS. 19A to 19C . 
       FIG. 19A  shows a cam lift of the camshaft.  FIG. 19B  is a time chart showing an energization period of the coil  13  in a case where the coil  13  is energized at BTDC θ 2 .  FIG. 19C  is a chart showing a behavior of the needle  26  in a case where the coil  13  is energized at BTDC θ 2 . A solid line “W” shows the behavior of the needle  26  in a case where the inner diameter of the communication hole  25  is 0.9 mm. A dashed line “X” shows the behavior of the needle  26  in a case where the inner diameter of the communication hole  25  is 0.4 mm. 
     First, based on the solid line “W”, the behavior of the needle  26  will be explained. At a time t 1 , the movable core  12  is magnetically attracted toward the fixed core  11 , and the needle  26  is positioned close to the fixed core  11 . At this time, as shown in  FIG. 19A , the plunger  42  slides up along with the cam and the high-pressure pump starts the discharging stroke. 
     When the coil  13  is deenergized at a time t 2 , the magnetic attraction force is extinguished. After a time t 3 , the needle  26  moves toward the pump chamber  47  and is brought into contact with the suction valve  20 . It should be noted that a time period from the time t 2  to the time t 3  corresponds to a time delay after the coil  13  is deenergized until the needle  26  starts moving. 
     After a time t 4 , the plunger  42  slides down, so that the pump chamber  47  is decompressed. The suction valve  20  and the needle  26  move toward the pump chamber  47 . When the inner diameter of the communication hole  25  is larger, the flow resistance of the fuel flowing between the movable core chamber  24  and the fuel supply passage  48  will become smaller. Thus, in a case shown by the solid line “W”, the needle  26  moves toward the pump chamber  47  at the time t 6 , and then the needle  26  and the movable core  12  bounce toward the fixed core  11 . At a time t 7 , the needle  26  bounces to a position which is close to a half position of a maximum needle lift quantity. After a time t 8 , the plunger  42  slides up and a metering stroke is started. When the coil  13  is energized at BTDC  02 , that is, at the time t 5 , a magnetic attraction force acts on the movable core  12  after a specified time delay. At a time t 9 , the needle  26  starts moving toward the fixed core  11 . The needle  26  is positioned most close to the fixed core  11  at a time t 10 . Thereby, a fuel discharging stroke is started. 
     Next, based on the dashed line “X”, the behavior of the needle  26  will be explained. The needle  26  is positioned most close to the fixed core side  11  at a time t 11 . Then, the high-pressure pump starts the discharging stroke. When the coil  13  is deenergized at the time t 2 , the magnetic attraction force is extinguished. After the time t 3 , the needle  26  moves toward the pump chamber  47  and is brought into contact with the suction valve  20 . When the pump chamber  47  is decompressed, the suction valve  20  and the needle  26  move toward the pump chamber  47 . When the inner diameter of the communication hole  25  is smaller, the flow resistance of the fuel flowing between the movable core chamber  24  and the fuel supply passage  48  will become larger. Thus, in the case shown by the dashed line “X”, a bounce amount of the needle  26 , which has moved toward the pump chamber  47  at the time t 12 , is small. The needle  26  slightly bounces at the time t 13 . After that, the needle  26  has been positioned in the pump chamber  47 . After a time t 8 , the plunger  42  slides up and a metering stroke is started. When the coil  13  is energized at BTDC  02 , that is, at the time t 5 , a magnetic attraction force acts on the movable core  12  after a specified time delay. After the time t 14 , the needle  26  starts moving toward the fixed core  11 . At the time t 15 , the needle  26  is positioned most close to the fixed core  11 . Thereby, a fuel discharging stroke is started. 
     As explained above with reference to  FIG. 19 , in a case where the inner diameter of the communication hole  25  is 0.9 mm, the needle  26  which has moved to the pump chamber  47  makes a large bounce with the movable core  12 . Therefore, when the coil  13  is energized at BTDC θ 2 , the magnetic attraction force acts on the movable core  12  after a specified time delay. While the needle  26  is bouncing, the needle  26  starts moving toward the fixed core  11 . A start time of the fuel discharging stroke is made earlier than intended, whereby the fuel discharged amount is increased. 
     Meanwhile, in a case that the inner diameter of the communication hole  25  is 0.4 mm, the needle  26  which has moved toward the pump chamber  47  slightly bounces and then the needle  26  is positioned most close to the pump chamber  47 . When the coil  13  is energized at BTDC θ 2  and the magnetic attraction force acts on the movable core  12 , the needle  26  starts moving from the pump chamber  47  toward the fixed core  11 . Therefore, since the fuel discharging stroke is started at normal time, the fuel discharged amount is not increased. 
       FIG. 20  is a graph showing a relationship between the opening sectional area (mm 2 ) of the communication hole  25  and a valve-close-response time (ms) of the suction valve  20 . 
     When the opening sectional area of the communication hole  25  is made smaller, the flow resistance of the fuel flowing between the movable core chamber  24  and the fuel supply passage  48  becomes larger. Thus, a time delay between the coil energization and the needle moving becomes larger. 
     When the rotating speed of a cam shaft is 4000 rpm and the valve-close-response time becomes greater than or equal to 2.2 ms, it will become difficult to control of the fuel pump. Moreover, if the inner diameter of a communication hole  25  is less than 0.4 mm, it will become difficult to form the communication hole  25  by machining. Therefore, the inner diameter of a communication hole  25  is greater than or equal to 0.4 mm. 
     Also, as shown in  FIG. 17 , in a case that the inner diameter of the communication hole  25  is less than or equal to 0.5 mm, the fuel discharged amount is more decreased as the energization start time of the coil  13  is more delayed. Therefore, it is preferable that the inner diameter of a communication hole  25  is 0.4 mm to 0.5 mm. 
     At this time, the opening sectional area of the communication hole  25  is 0.20% to 0.31% relative to a cross-sectional area of the movable core  12  from which the cross-sectional area of the needle  26  is removed. 
     According to the above second embodiment, following functional advantages can be achieved. 
     (1) In second embodiment, the inner diameter of the communication hole  25  is defined in such a manner that the starting time of the metering stroke is delayed and the fuel discharged amount is more decreased as the energization start time of the coil  13  is more delayed. Specifically, the inner diameter of a communication hole  25  is 0.5 mm or less. That is, the opening sectional area of the communication hole  25  is 0% to 0.31% relative to the cross-sectional area of the movable core  12  from which the cross-sectional area of the needle  26  is removed. 
     Thereby, in the suction stroke, it is restricted that the movable core  12  and the needle  26  bounce toward the fixed core  11  after the needle  26  biases the suction valve  20  toward the stopper by means of a biasing force of the second spring  14 . Therefore, the relationship between the energization start time of the coil  13  and the fuel discharged amount is properly maintained, so that the fuel discharged amount of the high-pressure pump can be controlled correctly. 
     (2) The opening sectional area of the communication hole  25  is 0.20% or more relative to the cross-sectional area of the movable core  12  from which the cross-sectional area of the needle  26  is removed. Thereby, the valve-close-response time of the suction valve  20  becomes shorter, and the high-pressure pump can be well controlled even when the cam shaft rotates at high speed. 
     (3) The opening sectional area of the communication hole  25  is 0.4 mm 2  or more. Thereby, the communication hole  25  of the needle guide  16  can be formed by machining, so that its manufacturing cost can be reduced. 
     (4) The pump chamber  47  and the valve chamber  200  communicate with each other through the radial grooves  71  and the axial grooves  70 . The passage sectional area of the radial grooves  71  is smaller than the passage sectional area of the axial grooves  70 . Thereby, when the suction valve  20  starts moving from the valve-close position to the valve-open position immediately after the suction stroke is started, the fuel flows from the valve chamber  200  to the pump chamber  47  without receiving a flow resistance of the fuel in the valve chamber  200 . A valve open speed of the suction valve  20  is enhanced. As a result, the suction efficiency of the fuel from the fuel supply passage  48  to the pump chamber  47  can be enhanced. 
     Meanwhile, in the metering stroke, since the fuel flowing into the valve chamber  200  from a pump chamber  47  is restricted, a fuel pressure increase in the valve chamber  200  is restricted and the self-close limit speed can be made higher. 
     Both the suction efficiency and the self-close limit speed are improved. The fuel discharged amount of the high-pressure pump can be surely controlled even when the engine speed is increased and a reciprocating speed of the plunger  42  is increased. 
     Other Embodiment 
     In the above embodiments, the solenoid valve  10  is a normally opened valve which is opened when the coil  13  is not energized. Meanwhile, the solenoid valve  10  may be a normally closed valve which is closed when the coil  13  is not energized. 
     In the above embodiments, the suction valve  20  and the needle  26  are formed independently. Meanwhile, the suction valve  20  and the needle  26  may be formed integrally from one piece. 
     In the second embodiment mentioned above, the radial grooves  71  are formed on the contacting portion  171  of the stopper  17 , and the axial grooves  70  are formed on the second guide portion  172  of the stopper  17 . Meanwhile, the radial grooves  71  may be formed on an end surface of the suction valve, which is opposite to the valve seat. The axial grooves  70  may be formed on the first guide portion  202  of a suction valve  20 . Moreover, an orifice may be provided at a sliding portion between the first guide portion  202  and the second guide portion  172 . 
     The present invention is not limited to the embodiments mentioned above, and can be applied to various embodiments.