Patent Grant
7284712
This application is based on and incorporates herein by reference Japanese Patent Application No. 2004-135371 filed on Apr. 30, 2004, Japanese Patent Application No. 2005-20904 filed on Jan. 28, 2005, Japanese Patent Application No. 2005-40730 filed on Feb. 17, 2005 and Japanese Patent Application No. 2005-67272 filed on Mar. 10, 2005.
1. Field of the Invention
The present invention relates to an injector and more particularly to a structure for controlling a nozzle needle of the injector, which is driven to enable and disable inject fuel.
2. Description of Related Art
In an injector used in a common rail type fuel injection system of a diesel engine, a nozzle needle, which is driven to enable and disable fuel injection, is controlled by an actuator, such as a solenoid, to freely set fuel injection timing and an amount of fuel injection and thereby to achieve advanced fuel injection. One previously proposed injector includes a nozzle needle back pressure chamber, which exerts a back pressure of the nozzle needle upon supply of pressurized fuel (see, for example, Japanese Unexamined Patent Publication No. H08-49620). When the pressure of the nozzle needle back pressure chamber is increased or decreased, the nozzle needle is moved between a seated position and a lifted position relative to a valve seat. A release passage and a control valve chamber are formed in the injector. The release passage releases the pressure of the nozzle needle back pressure chamber to a low pressure source, and the control valve chamber forms an intermediate pat of the release passage. When a control valve, which is arranged in the control valve chamber, is driven to enable and disable communication between the nozzle needle back pressure chamber and the low pressure source, the pressure of the nozzle needle back pressure chamber is increased and decreased. The control valve is seatable against a seat formed in an outer peripheral part of a port of the control valve chamber, which is communicated with the nozzle needle back pressure chamber. The pressure of fuel of the port is applied to the control valve in a valve opening direction, and a spring force is applied to the control valve in a valve closing direction. When the solenoid attracts an armature, which is formed integrally with the control valve, the control valve is lifted against the spring force.
Here, the spring force is set to maintain the closed state of the control valve at the time of deenergizing of the solenoid. The required attractive force of the solenoid is determined based on the spring force.
When downsizing of the actuator (e.g., downsizing of the solenoid) needs to be achieved, the attractive force of the solenoid is also reduced due to a decrease in a magnetic surface area of the solenoid. Thus, the spring force should be also reduced, and the fuel pressure, which is applied to the control valve in the lifting direction, should be also reduced.
The fuel pressure, which is applied to the control valve in the lifting direction, can be reduced by sufficiently reducing a diameter of the seat of the control valve to reduce a pressure receiving surface area. However, due to the choking effect or throttling effect induced by reducing of the diameter of the seat, a pressure decreasing speed of the nozzle needle back pressure chamber may be excessively slowed to affect the responsibility of the nozzle needle. Furthermore, when an orifice is provided in the release passage to adjust the pressure decreasing speed of the nozzle needle back pressure chamber, an adjustable range is relatively narrow due to the above throttling effect. When the passage cross sectional area in the opened state of the control valve needs to be increased, the lift amount of the control valve can be increased. However, the attractive force of the solenoid valve is inversely proportional to a distance between the armature and the magnetic pole. Thus, in the case of increasing the lift amount of the control valve, a relatively large attractive force is required, and therefore the downsizing of the solenoid cannot be achieved.
The present invention addresses the above disadvantage. Thus, it is an objective of the present invention to provide an injector, which includes an actuator of a minimum size and which achieves a sufficient passage cross sectional area at time of opening a control valve.
To achieve the objective of the present invention, there is provided an injector, which includes an elongated base body. An injection hole penetrates through a wall of the base body to inject fuel. A nozzle chamber is directly communicated with the injection hole on an upstream side of the injection hole in the base body and is supplied with pressurized fuel. A nozzle needle is located in the nozzle chamber and is driven to enable and disable injection of the fuel through the injection hole. A nozzle needle back pressure chamber is formed adjacent to a base end of the nozzle needle in the base body and is supplied with pressurized fuel to exert a back pressure of the nozzle needle for urging the nozzle needle toward the injection hole. A release passage is formed in the base body to release the pressure of the nozzle needle back pressure chamber to an external low pressure source. A control valve chamber is located in an intermediate part of the release passage in the base body. A first control valve is located in the control valve chamber and is driven to connect and disconnect between the nozzle needle back pressure chamber and the low pressure source. A valve drive means for driving the first control valve is provided. The valve drive means is a hydraulic valve drive means that includes a hydraulic pressure passage, a second control valve and an actuator. The hydraulic pressure passage is formed in the base body, such that the hydraulic pressure passage is supplied with pressurized fuel and applies the pressurized fuel to the first control valve as control hydraulic fluid for driving the first control valve. The second control valve is driven to control a flow of the fuel in the hydraulic pressure passage. An actuator drives the second control valve.
The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:
The injector includes an elongated base body 2 of a generally cylindrical configuration. The base body 2 includes a nozzle body 21, a distance piece 22, a first valve body 23, a holder 24 and a retaining nut 25. The nozzle body 21, the distance piece 22, the valve body 23 and the holder 24 are axially arranged in this order from a downstream end side of the injector and are held together by the retaining nut 25.
Various recesses and holes are formed in the base body 2 to receive corresponding components and to form fuel passages. A nozzle arrangement 11, which projects into a combustion chamber of the corresponding cylinder, is provided in a lower end of the injector, which is a bottom side in
A coil spring 32 is received in the longitudinal hole 211 and is held around the nozzle needle 31 to urge the nozzle needle 31 in the downward direction, i.e., in a seating direction. A nozzle needle back pressure chamber 53, which exerts the back pressure of the nozzle needle 31, is defined above the sliding portion of the nozzle needle 31 at a location adjacent to a base end of the nozzle needle 31. More specifically, the distance pieces 22 forms an upper wall of the nozzle needle back pressure chamber 53, and the upper end (the base end) of the nozzle needle 31 forms the lower wall of the nozzle needle back pressure chamber 53. The fuel pressure is applied from the high pressure passage 61 to the nozzle needle 31 in the lifting direction of the nozzle needle 31, which is away from the valve seat. When the pressure of the needle back pressure chamber 53 becomes equal to or less than a predetermined valve opening start pressure, the nozzle needle 31 is lifted from the valve seat. When the pressure of the needle back pressure chamber 53 becomes equal to or greater than a valve closing start pressure, the nozzle needle 31 is seated against the valve seat to stop the fuel injection.
The switching of the pressure of the nozzle needle back pressure chamber 53 is performed by the following structure. A longitudinal hole 231 extends in the first valve body 23 in the axial direction of the injector, and a cross sectional area of a lower end of the longitudinal hole 231 is enlarged to form an enlarged diameter portion (an enlarged cross sectional portion) of the longitudinal hole 231, which constitutes a first control valve chamber 54. A first valve needle 33, which serves as a first control valve, is located in the first control valve chamber 54. The first valve needle 33 is formed into a cylindrical body and includes a neck, which has a reduced diameter, near the lower end of the first valve needle 33. A shaft portion 33b of the first valve needle 33, which is located above the neck of the first valve needle 33 in
The distance piece 22 is interposed between the first valve body 23, which forms the first control valve chamber 54, and the nozzle body 21, which forms the nozzle needle back pressure chamber 53. Thus, the distance piece 22 forms a lower wall portion of the first control valve chamber 54 and an upper wall portion of the nozzle needle back pressure chamber 53. Furthermore, a through hole penetrates through the distance piece 22 in the axial direction of the injector to form a communication passage 63, which always communicates between the first control valve chamber 54 and the needle back pressure chamber 53. An orifice (a choke) 631 is formed in an intermediate location of the communication passage 63.
A high pressure branch passage (a communication passage) 64 having an orifice (a choke) is formed in the first valve body 23 having the first control valve chamber 54. The high pressure branch passage 64 is branched from the high pressure passage 61 and is communicated with the first control valve chamber 54. A distal end of the high pressure branch passage 64 is opened in a peripheral wall surface of the longitudinal hole 231 at the neck of the first valve needle 33 and is always communicated with the outer peripheral annular space 333 of the neck of the first valve needle 33. A low pressure branch passage 65 is formed in the distance piece 22. The low pressure branch passage 65 is branched from a low pressure passage 62 and is communicated with the first control valve chamber 54. The low pressure branch passage 65 is opened in the lower wall surface of the first control valve chamber 54 at an opposed position, which is opposed to the lower end surface of the first valve needle valve body 33a.The open end of the low pressure branch passage 65 forms a port 65a.The port 65a is closed when the first valve needle 33 is moved downward and is engaged with the lower wall surface of the first control valve chamber 54. An outer peripheral edge of this open end of the low pressure branch passage 65 forms a seat (a lower seat), to which the first valve needle 33 is seated. When the first valve needle 33 is moved upward, the upper tapered portion of the first valve needle valve body 33a is seated against a stepped surface of the first control valve chamber 54, which forms a seat (an upper seat) 542.
An orifice 651, which serves as a choke, is formed in the low pressure branched passage 65 at a location immediately downstream of the port 65a.
A valve drive arrangement 12, which serves as a valve drive means (a hydraulic drive means) for controlling the first valve needle 33, will be described below. The first valve needle 33 is moved through an increase or a decrease of a pressure of a valve back pressure chamber 55, which is formed above the shaft portion 33b.The valve back pressure chamber 55 receives the high pressure fuel from the high pressure passage 61 and the high pressure branch passage 64 through a longitudinal hole 331 and a lateral hole 332 of the first valve needle 33. The longitudinal hole 331 extends from an upper end surface of the first valve needle 33 to the neck of the first valve needle 33. The lateral hole 332 radially extends from an outer peripheral surface of the first valve needle 33 to the longitudinal hole 331 at the neck of the first valve needle 33.
The valve back pressure chamber 55 is communicated with a second control valve chamber 56 through a communication passage 66. The communication passage 66 is formed as a small diameter hole, which extends from a top of the longitudinal hole 231 of the first valve body 23 to an upper end surface of the first valve body 23. An orifice (a choke) 661 is formed in an intermediate point of the communication passage 66.
The second control valve chamber 56 is formed by the first valve body 23 and a recess formed in a lower end surface of a second valve body 26. The first valve body 23 forms a lower end wall of the second control valve chamber 56. An outer peripheral edge 26a of the recess of the lower end surface of the second valve body 26 forms an annular projection, which is press fitted to an annular groove formed in the upper end surface of the first valve body 23, so that the first valve body 23 and the second valve body 26 are fitted together.
In the second control valve chamber 56, the opening end of the communication passage 66, which is opened at the lower wall surface of the second control valve chamber 56, forms a port 66a that is communicated with the valve back pressure chamber 55. The second control valve chamber 56 is always communicated with the low pressure passage 62 at an outer peripheral edge of the second control valve chamber 56.
A longitudinal hole 261, which extends through an upper wall of the second control valve chamber 56, is formed in the second valve body 26. A second valve needle 36 is slidably received in the longitudinal hole 261. A lower end of the second valve needle 36 projects into the second control valve chamber 56, and an upper end of the second valve needle 36 projects in a solenoid chamber (a receiving chamber) 57, which is located at an upper side of the second valve body 26.
The lower end of the second valve needle 36 holds a valve body 35, which serves as a second control valve that has a semispherical shape. The second valve needle 36 moves integrally with the valve body 35. A flat lower end surface of the valve body 35 is opposed to the lower wall surface of the second control valve chamber 56 and the port 66a.A seat surface 561, to which the valve body 35 is seated, is formed in an outer peripheral edge of the port 66a.When the valve body 35 is seated against the seat surface 561, the communication between the second valve chamber 56 and the valve back pressure chamber 55 is disconnected.
A circular disk shaped armature 37 is secured to an upper end of the second valve needle 36, which projects into the solenoid chamber 57. The armature 37 is opposed to a magnetic pole surface of a solenoid (actuator) 121 arranged in the solenoid chamber 57. In the solenoid 121, coils 42 are wound around an annular space of a stator 41, which includes two coaxial cylindrical bodies. Electric power is supplied from lead wires 43 to the coils 42. A coil spring 38 is radially inwardly received in the stator 41 and resiliently contacts the armature 37. The coil spring 38 urges the armature 37 in a direction away from the stator 41. The solenoid 121 is clamped between the second valve body 26 and a closing member 27 and is received in a longitudinal hole 241 of the holder 24 along with the second valve body 26 and the closing member 27. A seal member 44 seals between the closing member 27 and the holder 24.
In contrast, when the solenoid 121 is turned off, i.e., is deenergized, and thereby the second valve needle 36 is moved downward, the communication between the valve back pressure chamber 55 and the low pressure passage 62 is disconnected. Thus, the pressure of the valve back pressure chamber 55 is increased by the high pressure fuel that is supplied to the valve back pressure chamber 55 through the passage, which includes the high pressure passage 61, the high pressure branch passage 64, the lateral hole 332 of the first valve needle 33 and the longitudinal hole 331 of the first valve needle 33. In this way, the first valve needle 33 is lifted away from the upper seat 542 and is seated against the lower seat 541. In this state, the communication between the first control valve chamber 54 and the lower pressure chamber 62 is disconnected, and the high pressure fuel is supplied to the needle back pressure chamber 53 through the corresponding passage, which includes the high pressure passage 61, the high pressure branch passage 64, the first control valve chamber 54 and the communication passage 63. Thus, the pressure of the nozzle needle back pressure chamber 53 is increased. When the pressure of the nozzle needle back pressure chamber 53 becomes equal to or greater than the valve closing start pressure, the nozzle needle 31 is seated against the valve seat, i.e., is placed in the valve closed state.
The injector of the present embodiment is constructed in the above manner.
In this way, the seat diameter and the lift amount of the first valve needle 33 can be made large enough regardless of the size of the solenoid 121. Thus, the operational characteristics of the nozzle needle 31 can be more freely adjusted by the orifice 631 that is provided in the communication passage 63, which communicates between the nozzle needle back pressure chamber 53 and the first control valve chamber 54.
Furthermore, in the injector of the present embodiment, as discussed above, the orifice 651 is formed adjacent to the port 65a on the downstream side of the port 65a in the low pressure branch passage 65, which extends from the port 65a of the first control valve chamber 54 to the low pressure passage 62. Thus, even when the first valve needle 33 is lifted from the lower seat 541, the pressure in the space between the first valve needle 33 and the lower seat 541 does not decrease rapidly due to the throttling effect of the orifice 651. Therefore, the relatively high pressure remains in the space between the first valve needle 33 and the lower seat 541 at the time of lifting the first valve needle 33 from the lower seat 541. This remaining pressure is exerted in the accelerating direction for accelerating the valve opening of the first valve needle 33 by assisting the lifting of the first valve needle 33, and this remaining pressure is also exerted in the direction for maintaining the lifting of the first valve needle 33. Thus, the operational stability of the first valve needle 33 is increased, and the operational variations of the injector can be alleviated.
The base body 2A of the second embodiment is basically the same as that of the first embodiment. However, a distance piece 22a and a closing member 27A of the second embodiment are different from the distance piece 22 and the closing member 27 of the first embodiment. A high pressure branch passage 67, which branches from the high pressure passage 61 and is communicated to the needle back pressure chamber 53, is formed in the distance piece 22A to always communicate between the needle back pressure chamber 53 and the high pressure passage 61. An orifice (a choke) 671 is formed in the high pressure branch passage 67. In this way, as shown in
The structure of the armature 37A is basically the same as that of the first embodiment. A spacer 39 is provided in an opposed surface of the armature 37A, which is opposed to the stator 41. The spacer 39 is a circular disk member, which has a diameter larger than that of the coil spring 38. An annular protrusion 39a is formed in an outer peripheral edge of the spacer 39. In a state where an upper surface of the annular protrusion 39a is engaged with the stator 41, the second valve needle 36 is placed in a fully lifted state. By changing the setting of the height of the protrusion 39a, an air gap between the armature 37A and the stator 41 in the fully lifted state of the second valve needle 36 is adjusted.
The seal member of the closing member 27 of the first embodiment is eliminated from the closing member 27A of the second embodiment. In the second embodiment, the closing member 27A is press fitted into the longitudinal hole 241 to seal between the closing member 27A and the longitudinal hole 241, so that the number of the components is reduced.
The high pressure passage 61B, which is formed in the base body 2B, is basically the same as the high pressure passage 61 of the first embodiment. The only difference from the first embodiment is that an accumulator chamber 58 is provided in the high pressure passage 61B. The accumulator chamber 58 is arranged on the lateral side of the longitudinal hole 241 at the location where the small diameter portion for receiving the lead lines 43 of the longitudinal hole 241 is provided. In this way, the sufficient outer peripheral wall thickness of the accumulator chamber 58 can be maintained.
The accumulator chamber 58 is formed in the following manner. In the present embodiment, as shown in
In this way, the accumulator chamber 58 can be formed without thinning the wall of the base body 2B at the outer peripheral part of the accumulator chamber 58. Furthermore, the members 7a, 7b are not mechanically joined in the present embodiment, so that the size of the injector is not substantially increased.
Influences of the pressure of the first control valve chamber 54 against the lifting of the first valve needle 33 will be described with reference to
When this phenomenon is repeated, it may cause vibrations of the first valve needle 33, which in turn causes variations in the amount of fuel injection, or which in turn causes wearing of the valve seats. The present embodiment addresses the above disadvantage and promotes the practical use of the injector.
The base body 2C of this embodiment is basically the same as that of the first embodiment. However, the first valve body 23C, which forms the base body 2C, is different from that of the first embodiment. In the first valve body 23C, the high pressure branch passage 64, which extends from the high pressure passage 61, is branched at the point that is on the upstream side of the opening of the high pressure branch passage 64 to the outer peripheral annular space 333 located at the neck of the first valve needle 33. This branched part of the high pressure branch passage 64 is opened in the inner peripheral wall of the first control valve chamber 54 to form a continuously connected passage 68, which always communicates between the high pressure passage 64 and the first control valve chamber 54. The continuously connected passage 68 forms the communication passage, which directly communicates between the high pressure branch passage 64 and the first control valve chamber 54 without passing through the outer peripheral annular space 333. Furthermore, an orifice (a choke) 681 is provided in the continuously connected passage 68. In this way, even when the first valve needle 33 is seated against the upper seat 542, the small amount of high pressure fuel is supplied to the first control valve chamber 54 upon being restricted by the orifice 681. Thus, the pressure of the first control valve chamber 54 does not decrease excessively, and therefore it is possible to limit fluctuations of the seating position of the first valve needle 33.
The position of the continuously connected passage 68 is not limited to that of the fourth embodiment and can be changed to any other suitable position, which communicates between the first control valve chamber 54 and the high pressure passage 61. In the fifth embodiment of
Even in the fifth and sixth embodiments, similar to the fourth embodiment, the fluctuations in the pressure of the first control valve chamber 54 can be limited to limit vibrations of the first valve needle 33. In the sixth embodiment, the structure is substantially similar to that of the second embodiment. Through the adjustment of the valve opening and closing speeds of the first valve needle 33, the reduction in the exhaust gas emission can be achieved simultaneously with the increase in the lifetime of the injector through the reduction in variations of the fuel injection and the limitation of the wearing of the valve seats. The inner diameter of the orifice 681, which is provided in the continuously connected passage 68 of the fourth to sixth embodiments, is determined in connection with the inner diameter of the orifice 651, which is provided on the downstream side of the port 65a to communicate between the first control valve chamber 54 and the low pressure branch passage 65. In the sixth embodiment, the inner diameter of the orifice 681 is determined also in connection with the inner diameter of the orifice 631, which is provided in the communication passage 63 connected to the nozzle needle back pressure chamber 53.
Switching leakage of the control valve will be described with reference to
The time difference between the lifting of the armature 37 and the lifting of the first valve needle 33 is very small, so that the fuel of the valve back pressure chamber 55 and the fuel of the nozzle needle back pressure chamber 53 are substantially simultaneously supplied to the solenoid chamber 57 (see the arrow in the drawing). Thus, the pressure surge is generated in the solenoid chamber 57, and the hydraulic pressure, which is applied to the armature 37, varies. When the valve closing speed of the valve body 33a, which is provided in the lower end of the first valve needle 33, varies due to the variation of the hydraulic pressure applied to the armature 37, the amount of fuel injection may be varied. Particularly, in the case of pilot injections for injecting fuels several times within a short time period, there is a substantial influence. For example, the surge of the switching leakage caused by the previous injection may cause a change in the valve opening speed in the next injection. The present embodiment addresses the above disadvantage and promotes the practical use of the injector.
In the outer peripheral part of the second valve body 26, there is provided the low pressure passage 262, which is communicated with the low pressure passage 62 at the upper end of the first valve body 23. In the second valve body 26, one end of the low pressure passage 263 is opened in the bottom wall of the solenoid chamber 57, and the other end of the low pressure passage 263 is opened in the outer peripheral surface of the second valve body 26 to communicate with the low pressure passage 262. A check valve 8 is provided in a connecting end of the low pressure passage 263, which is connected to the low pressure passage 262. The check valve 8 permits the fuel flow only from the solenoid chamber 57 toward the low pressure passage 62. As shown in
With this structure, when the switching leakage occurs, the fuel of the valve back pressure chamber 55 and the fuel of the nozzle needle back pressure chamber 53 are substantially simultaneously supplied to the low pressure passage 262. However, due to the presence of the check valve 8, only the small amount of fuel, which has passed the orifice 83, is supplied to the low pressure passage 263 (see the arrow in the drawing). Thus, the substantial pressure surge does not occur in the solenoid chamber 57, and therefore it is possible to limit a change in the valve closing speed caused by a change in the hydraulic pressure applied to the armature 37. Therefore, even in the case of the pilot injections for injecting fuel several times within the short time period, it is possible to limit occurrence of variations in the amount of fuel injection. As a result, the fuel injection controllability is improved.
In contrast, as shown in
The orifice 83 is provided to remove air from the solenoid chamber 57 after the assembly of the injector. In this case, since the leakage from the sliding components is relatively small, the air can be removed from the solenoid chamber 57 through the orifice 83 by supplying fuel through the low pressure passages 262, 263. However, in the case where the removal of the air is not necessary, the orifice 83 may be eliminated.
Preferred position and arrangement of each main component of the above respective embodiments will be described with reference to
When the second valve needle 36 is arranged to be eccentric to the center point 2a of the base body 2, the space, which is provided radially outward of the high pressure passage 61, can be maximized. That is, since the high pressure fluid passes through the high pressure passage 61, the passage wall of the high pressure passage 61 needs to have the sufficient thickness to achieve the sufficient strength. With the structure shown in
Similar to
The center of the nozzle needle 31 (
Diameter (Outflow Rate) of Orifice 661≧Diameter (Inflow Rate) of Lateral Hole 332.
In this way, the pressure of the valve back pressure chamber 55 can be reliably decreased at the time of moving the second valve needle 36 in the upward direction through energization of the solenoid 121.
As shown in
That is, the following two conditions should be satisfied:
Cross Sectional Area of Orifice 651<Surface Area defined by lower End surface 334 and Port 65a; and
Diameter D2 of Orifice 651<Diameter D1 of Port 65a.
When the first valve needle 33 is lifted from the lower seat 541, fuel flows, as indicated by the arrows in
As shown in
Outer Diameter of Valve Body 33a>Diameter D3 of Longitudinal Hole 231.
The first valve needle 33, which is a movable member, slidably contacts the longitudinal hole 231 of the first valve body 23 through the shaft portion 33b.When the above settings are implemented, a tapered surface 33d of the valve body 33a of the first valve needle 33 is engaged with a lower end corner 231a of the longitudinal hole 231. That is, the first valve needle 33 can be limited from lifting by the first valve body 23.
Furthermore, when the diameter of the orifice 631, which is provided in the communication passage 63 connected to the needle back pressure chamber 53, is denoted by D4, the surface area (π×D3×H), which is defined by the corner 231a and the tapered surface 33d, is set to be larger than the cross sectional area (π/4×D4×D4) of the orifice 631.
When the first valve needle 33 is lifted from the upper seat 542, fuel flows, as indicated by the arrows in
The relationship between the cross sectional area (π/4×D4×D4) of the orifice 631 and the cross sectional area (π/4×D2×D2) of the orifice 651 of
In this way, the pressure increasing speed and the pressure decreasing speed of the nozzle needle back pressure chamber 53 (
As shown in
In
Coil Spring 32>Coil Spring 38>Coil Spring 34.
This is due to the following reason. First, the coil spring 32 defines the valve closing speed of the nozzle needle, so that the coil spring 32 requires the maximum preload. That is, at the time of starting the closing of the nozzle needle 31, the pressure of the nozzle chamber 51 and the pressure of the nozzle needle back pressure chamber 53 substantially coincide with each other, and also the pressure receiving area of the nozzle chamber 51 and the pressure receiving area of the nozzle needle back pressure chamber 53 substantially coincide with each other. Thus, the force, which is caused by the pressure of the nozzle chamber 51, and the force, which is caused by the pressure of the nozzle needle back pressure chamber 53, are substantially balanced to each other. Thus, the valve closing speed of the nozzle needle is set based on the urging force of the coil spring 32.
Next, the coil spring 38 needs to have the preload, which closes the port 66a against the high pressure fluid applied to the port 66a.Here, the diameter of the port 66a is denoted by “D5”, and the pressure of the fluid applied to the port 66a is denoted by “P” (e.g., 200 MPa). In such a case, the required preload of the coil spring 38 is expressed as follows:
Preload of Coil Spring 38>π/4×D5×D5×P+α
where α is an extra force, for compensating an error or the like.
The coil spring 34 requires a little preload since the pressure of the valve back pressure chamber 55 and the pressure of the first control valve chamber 54 substantially coincide with each other, and therefore the valve back pressure chamber 55 and the first control valve chamber 54 are substantially balanced to each other. Here, the urging force for downwardly urging the first valve needle 33 is expressed by:
π/4×D3×D3×P1+spring preload
where D3 is a diameter of the shaft portion 33b and P1 is a pressure of the valve back pressure chamber 55. The urging force for upwardly urging the first valve needle 33 is expressed by:
π/4×(D3×D3−D1×D1)×P2
where D1 is the diameter of the port 65a, and P2 is a pressure of the first control valve chamber 54, and D3>D1, and P1=P2. Thus, the hydraulic pressure applied to the first valve needle 33 is substantially balanced.
Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-135371 | Apr 2004 | JP | national |
| 2005-020904 | Jan 2005 | JP | national |
| 2005-040730 | Feb 2005 | JP | national |
| 2005-067272 | Mar 2005 | JP | national |
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| Number | Date | Country | |
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| 20050242211 A1 | Nov 2005 | US |
