Fuel injection apparatus

According to the present invention, a fuel injection apparatus includes a casing having a control pressure chamber for storing fuel supplied from fuel passage, a needle valve to which fuel stored in the control pressure chamber applies pressure in the valve closing direction, a valve device for interrupting communication between the fuel passage and the control pressure chamber to seal fuel in said control pressure chamber, and volume changing device for expanding volume of the control pressure chamber after fuel is sealed in the control pressure chamber by the valve device. According to the above fuel injection device, pressure in the control pressure chamber is reduced while the fuel is stored therein by the volume changing device, the nozzle needle is lifted, and injection is started. For this reason, it is not necessary to supply surplus fuel in addition to the injection fuel during the fuel injection. In this way, the fuel supply pump is made smaller in size, and efficiency for use of supplied fuel can be improved. Further, since high-pressure fuel is not discharged from the fuel injection apparatus, pulsation within the common rail can be suppressed, and fuel injection can be stabilized.

CROSS REFERENCE TO RELATED APPLICATION 
The present application is based on and claims priority from Japanese 
Patent application No. 6-299839 filed on Dec. 2, 1995, the content of 
which is incorporated herein by reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a fuel-injection apparatus for an internal 
combustion engine. 
2. Related Art 
Conventionally, as illustrated in FIG. 12, the fuel injection apparatus 
having a control pressure chamber on opposite side of an injection port of 
a nozzle needle has been known, in which the start timing or the end 
timing of the fuel injection by the nozzle needle is controlled by 
adjusting pressure in the control pressure chamber (paper by IMH Co. at 
the Vienna Motor Symposium). 
In FIG. 12, an injector 140 includes a nozzle needle 142 slidably disposed 
in an axial direction within a casing 141, and fuel which is supplied from 
a common rail (not illustrated) through a fuel passage 151 to a fuel 
chamber 146 is injected from an injection opening 147. A piston 144 is 
disposed reciprocatably with the nozzle needle 142 on an opposite side of 
the injection opening 147 of the nozzle needle 142. The nozzle needle 142 
is urged by a compression coil spring 143 in a closing direction. A 
control pressure chamber 145 is defined by an end face of the piston 144 
on an opposite side of the nozzle needle 142 and an inner wall of the 
casing 141. Fuel is supplied through the orifice 153 from the fuel passage 
152 to the control pressure chamber 145. The control pressure chamber 145 
is also connected to a pressure control valve 150 through an orifice 154. 
The pressure control valve 150 is a two-position and two-port solenoid 
valve. Leaked fuel within the casing 141 is discharged from a fuel passage 
155 to a fuel tank (not illustrated.) When the pressure control valve 150 
is closed as shown in FIG. 12, high-pressure fuel from the common rail is 
supplied to the control pressure chamber 145 without being discharged to 
the fuel tank 145. Thus, the nozzle needle 142 is closed by the sum of 
urging force of a compression coil spring 143 and pressure, exerted upon a 
pressure-receiving surface of the piston 144, of the control pressure 
chamber 145. Additionally, when the pressure control valve 150 is open, an 
amount of fuel discharged from the control pressure chamber 145 to the 
fuel tank through orifice 154 and pressure control valve 150 is greater 
than an amount of fuel discharged from the common rail to the control 
pressure chamber 145, because passage area of the orifice 153 is smaller 
than that of the orifice 154. Accordingly, when pressure within the 
control pressure chamber 145 declines, the nozzle needle 142 is lifted by 
the pressure of high-pressure fuel in the fuel chamber 146, and fuel is 
injected from the injection opening 147. 
In the injector 140 illustrated in FIG. 12 high-pressure fuel keeps on 
being discharged to the fuel tank through the orifice 154, while the 
pressure control valve 150 is open. Therefore, an additional amount of 
fuel corresponding to the discharged amount must be supplied to the 
injector 140 in addition to the amount of injection fuel, and thereby the 
fuel supply pump for supplying fuel to the common rail becomes large in 
size and the efficiency of the fuel supply system is deteriorated. 
Moreover, when the pressure control valve 150 is closed, high-pressure 
fuel is supplied to the control pressure chamber 145 through the orifice 
153 and pressure within the control pressure chamber 145 rises gradually. 
Therefore, there is a problem in that closing of the nozzle needle is 
delayed. 
In order to solve the above problem of the delay in closing of the nozzle 
needle, the fuel injection apparatus illustrated in FIG. 13 has been 
proposed (paper by IMH Co. at the Vienna Motor Symposium). According to 
this apparatus, a communication between the fuel tank and the control 
pressure chamber 145 as well as a communication between the common rail 
and the control pressure chamber 145 are open and closed by a pressure 
control valve 161 which is a two-position and three-port solenoid valve. A 
check valve 163 for preventing fuel from flowing from the control pressure 
chamber 145 to the pressure control valve 161 and a pilot valve 162 having 
an orifice 164 are provided in a fuel passage. In FIG. 13, an injector 160 
is in a closed state. When the pressure control valve moves from a 
position, where the pressure control valve communicates with the fuel 
tank, to the position illustrated in FIG. 13 after the fuel injection 
ends, high-pressure fuel from the common rail is rapidly supplied to the 
control pressure chamber 145 passing through check valve 163, thereby 
closing delay of the nozzle valve 142 being prevented. 
Even in the fuel injection apparatus illustrated in FIG. 13, however, fuel 
is discharged from the control pressure chamber 145 to the fuel tank every 
time fuel is injected, therefore, it is necessary to supply, from the fuel 
supply pump to the common rail, several times as much fuel as the amount 
of injection fuel. For this reason, the fuel supply pump becomes large in 
size, and the diameter of fuel piping to supply fuel to the injector 160 
also becomes large, thereby causing a problem in which efficiency of the 
fuel supply system being deteriorated. Moreover, there is a problem in 
that the cost is increased because the structure of the pressure control 
valve 161 is complicated. 
SUMMARY OF THE INVENTION 
To solve the foregoing problems, it is an object of the present invention 
to provide a fuel-injection apparatus which can reduce an amount of fuel 
supplied to an injection valve without reducing an amount of injection 
fuel. 
According to the present invention, a fuel injection apparatus includes a 
casing having a control pressure chamber for storing fuel supplied from 
fuel passage, a needle valve to which fuel stored in the control pressure 
chamber applies pressure in the valve closing direction, a valve device 
for interrupting communication between the fuel passage and the control 
pressure chamber to seal fuel in the control pressure chamber, and volume 
changing device for expanding volume of the control pressure chamber after 
fuel is sealed in the control pressure chamber by the valve device. 
According to the above fuel injection device, pressure in the control 
pressure chamber is reduced while the fuel is stored therein by the volume 
changing device, the nozzle needle is lifted, and injection is started. 
For this reason, it is not necessary to supply surplus fuel in addition to 
the injection fuel during the fuel injection. In this way, the fuel supply 
pump is made smaller in size, and efficiency for use of supplied fuel can 
be improved. Further, since high-pressure fuel is not discharged from the 
fuel injection apparatus, pulsation within the common rail can be 
suppressed, and fuel injection can be stabilized.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the present invention will be described with 
reference to the drawings. 
FIG. 2 illustrates a structure of a fuel-feed system employing a 
fuel-injection device of the first embodiment according to the present 
invention. 
Fuel, which has been sucked from a fuel tank 1 by a low pressure fuel pump 
2, is pressurized by a high pressure fuel pump 3. The pressure of fuel is 
controlled to a predetermined pressure by a pressure regulator 5, and the 
fuel is supplied to a common rail 4. The pressure regulator 5 also 
functions as a safety valve to control the maximum fuel pressure. High 
pressure fuel kept at a predetermined pressure in the common rail 4 is 
supplied to an injector 10. Fuel pressure supplied to the injector 10, or 
injection signals transmitted to the injector 10, is controlled by an 
electronic control unit (ECU) 7 in accordance with engine speed, load, and 
environmental conditions based on signals from several sensors 9. 
Firstly, feedback control is performed on fuel pressure in accordance with 
a difference between a detected value of discharge amount of the fuel 
supply pump 3, which is detected by a pressure sensor 6 installed on the 
common rail 4, and a pressure target value, and a command output for 
injection signals is made from the ECU 7 so that the required injection 
timing and injection quantity are obtained. 
FIG. 1 illustrates a detailed structure of the injector 10. A casing member 
11 of the injector 10 is composed of a valve casing 11a, a tip gasket 11b, 
and a body lower 11c. The valve casing 11a, the tip gasket 11b, and the 
body lower 11c are integrally joined by a retaining ring 12. A sliding 
hole 14 is formed axially in the casing member 11, and a needle valve 20 
composed of a nozzle needle 21 and a piston 22 is reciprocatably disposed 
in the axial direction of the sliding hole 14. A fuel chamber 13 and an 
injection opening 16 are formed in the valve casing 11a so as to 
communicate with the sliding hole 14, and a guide portion 21a of the 
nozzle needle 21 is slidably guided by an inner wall of the casing member 
11 which forms the sliding hole 14. A valve body 21b is integrally formed 
on a tip of this nozzle needle 21, and fuel injection from the injection 
opening 16 is switched on and off by the valve body 21b being unseated 
from and seated in a valve seat 15. 
The piston 22 has a retainer 22b, which contacts the nozzle needle 21, at 
one end portion, and a compression coil spring 23 is retained by the 
retainer 22b. The piston 22 has a sliding portion 22a, which slides with 
the inner wall of the casing member 11 forming the sliding hole, at the 
other end portion, and space on each side in the axial direction of this 
sliding portion 22a is enclosed by the sliding portion 22a. The nozzle 
needle 21 is urged in a valve closing direction together with the piston 
22 by the compression coil spring 23. 
A solenoid valve 30 is provided above the casing member 11. A valve casing 
31 of the solenoid valve 30 houses a pressure control valve 40 slidably 
disposed in an axial direction within a sliding hole 34, and a wound coil 
51 is housed within a solenoid casing 50. 
The pressure control valve 40 is composed of a needle 41, a land portion 
42, and a guide portion 43, and small-diameter first and second connecting 
portions 44 and 45 which respectively connect between the needle 41 and 
land portion 42 and between the land portion 42 and guide portion 43. A 
seat portion 41a of the needle 41 seats on a valve seat 33 in an upward 
direction of FIG. 1 or unseats from the valve seat 33 in a downward 
direction of FIG. 1. The land portion 42 slides with an inner wall 34a 
forming the sliding hole 34 in a manner to form a clearance of several 
microns therebetween. 
Additionally, the fuel passage 32 is open in a fuel chamber within the 
pressure control valve 40, which is formed by the inner wall, first 
connecting portion 45, land portion 42, and guide portion 43. Therefore, 
high pressure from the fuel passage 32 is applied to a side wall of the 
needle 41, and reciprocating movement of the needle 41 within the inner 
wall is thereby facilitated. 
An armature 46 is secured to an end portion of the guide portion 43 by 
press-fitting, welding, threads, or the like, and reciprocates together 
with the pressure control valve 40. Downward movement of the armature 46 
is restricted by a retainer 35' of the valve casing 31. When electric 
current to the coil 51 is switched off, the needle 41 is unseated from the 
valve seat 33 by urging the armature 46 downwardly with the urging force 
of the compression coil spring 52. At this time, the land portion 42 moves 
downward to the pressure chamber 37 disposed below the needle 41, and the 
pressure chamber 37 communicates with a tubular space formed around 
connecting portion 45. When electric current to the coil 51 is switched 
on, the armature 46 is attracted toward the coil 51, i.e., the upward 
direction of FIG. 1. Thus, the pressure control valve 40 is lifted and the 
needle 41 is seated on the valve seat 33. At this time, the communication 
between the pressure chamber 37 and the space formed around the connecting 
portion 45 is interrupted. 
High-pressure fuel having been supplied from the common rail 4 to the 
injector 10 is supplied to the fuel chamber 13 from a fuel passage 24, a 
first fuel passage formed in the casing member 11. Pressure of fuel 
supplied to the fuel chamber 13 urges the nozzle needle 21 in a valve 
opening direction. High-pressure fuel having been supplied from the common 
rail 4 to the injector 10 is also supplied to the sliding hole 34 from a 
fuel passage 32, a second fuel passage formed in the valve casing 31. 
A pressure chamber 26 formed above the piston 22 communicates with the 
pressure chamber 37 formed below the pressure control valve 40 by a fuel 
passage 27 formed in the casing member 11 and a fuel passage 39 formed in 
the valve casing 31, and the pressure chamber 26, fuel passage 27, fuel 
passage 39, and pressure chamber 37 function as a control pressure chamber 
to apply pressure to the piston 22. In this embodiment, the fuel passage 
27 and fuel passage 39 communicates with an outer periphery of the 
pressure chamber 37, but these passages can communicate with a central 
portion instead of the outer periphery of the pressure chamber 37. 
Furthermore, the sliding hole 14 between the sliding portion 22a of the 
piston 22 and the guide portion 21a of the nozzle needle 21 communicates 
with a housing hole 36 which houses the armature 46 through a fuel passage 
28 formed in the casing member 11 and a fuel passage 29 formed in the 
valve casing 31, and surplus fuel within the sliding hole 14 and housing 
hole 36 is discharged to the fuel tank from a fuel discharge port 38 
communicating with the fuel passage 29. 
An operation of the injector 10 will be described hereinafter. 
FIG. 1 illustrates a state wherein electric current is supplied to the coil 
51. The armature 46 is attracted toward the coil 51 by magnetic field 
generated in the coil 51 resisting the urging force of the compression 
coil spring 52, thereby the pressure control valve 40 is lifted upwardly 
together with the armature 46. When the land portion 42 passes the valve 
seat 33 and is pulled upwardly within the sliding hole 34, communication 
between the space formed around the first connecting portion 45 and the 
pressure chamber 37 are interrupted by the land portion 42. Thus, 
high-pressure fuel is no longer supplied to the pressure chamber 37. When 
the pressure control valve 40 is further lifted together with the armature 
46 and the needle 41 is seated on the valve seat 33, the pressure control 
valve 40 is stopped. Since the control pressure chamber increases in its 
volume by a volume Vs, which is obtained by multiplying a movement 
distance of further movement upwardly of the land portion 42 after 
communication between the space formed around the connecting portion and 
the pressure chamber 37 is interrupted with the cross-sectional surface 
area of the land portion 42, while storing a predetermined amount of fuel 
defined by the pressure chamber 26, fuel passage 27, fuel passage 39, and 
pressure chamber 37, the pressure of the pressure chamber 36 drops. Then, 
the combined force of the force which urges the piston 22 downwardly in 
accordance with pressure within the pressure chamber 26 and the 
compression coil spring 23 gets weaker than the force obtained by 
multiplying the pressure of fuel supplied from the common rail 4 with the 
pressure-receiving surface area when the nozzle needle 21 is closed. Then, 
the nozzle needle is unseated from the valve seat 15, and high-pressure 
fuel is injected from the injection opening 16. 
The force relationship at this time is described. When the 
pressure-receiving cross sectional surface area of the sliding portion 22a 
is taken to be Ap, the cross-sectional surface area of the guide portion 
21a of the nozzle needle 21 is taken to be An, the pressure of fuel 
supplied from the common rail 4 is taken to be Pc, the pressure within the 
pressure chamber 26 is taken to be Pp, and load of the compression coil 
spring 23 is taken to be Fsp, a valve opening condition of the nozzle 
needle 21 is expressed by the following equation (1). 
EQU Ap.times.Pp+Fsp&lt;(An-As).times.Pc (1) 
That is to say, when pressure Pp of the pressure chamber 26 drops in a 
manner to satisfy the following equation (2), the nozzle needle 21 is 
lifted and fuel injection begins, as shown in FIG. 4. Pressure Pp is set 
not less than zero (equivalent to atmospheric pressure) to prevent 
cavitation from occurring due to the pressure reduction by the land 
portion 42. 
EQU 0&lt;Pp&lt;{(An-As).times.Pc-Fsp)/Ap (2) 
FIG. 3 illustrates a state where electric current to the coil 51 is off. 
When electric current to the coil 51 is switched off, the armature 46 is 
urged downwardly in FIG. 3 by the urging force of the compression coil 
spring 52, and the pressure control valve 40 also moves downwardly 
together with the armature 46. Then, the land portion 42 further moves 
lower than the position where the land portion 42 slides with the inner 
wall 34a and protrudes within the pressure chamber 37, and so the space 
formed around the first connecting portion 45 and the pressure chamber 37 
are communicated. That is to say, high-pressure fuel supplied from the 
common rail 4 is supplied from the fuel passage 32, space formed around 
the connecting portion 45, pressure chamber 37, and fuel passage 39, 
through the fuel passage 27, and to the pressure chamber 26. When pressure 
Pp within the pressure chamber 26 is satisfied with the following 
equations (3) and (4), the nozzle valve 21 begins to be lowered and stops 
when the valve body 21b seats on the valve seat 15, as shown in FIG. 4. 
EQU Ap.times.Pp+Fsp&gt;An.times.Pc (3) 
From equation (3), 
EQU Pp&gt;(An.times.Pc-Fsp)/Ap (4) 
Volume change Vp of the pressure chamber 26 by the movement of the piston 
22 is set to be smaller than volume change Vs by the land portion 42, and 
volume of the space which is the control pressure chamber defined and 
formed between the land portion 42 and the sliding portion 22a increases 
as the pressure control valve 40 moves upwardly, thereby pressure within 
the pressure chamber 26 being dropped. 
According to the first embodiment, it is simplified to control the opening 
and closing of the nozzle needle 21 by the pressure within the pressure 
chamber 26 which is regulated by changing the volume with the 
reciprocating movement of the pressure control valve 40. High-pressure 
fuel other than for fuel injection from the injection opening 16 is not 
discharged from the injector 10 at this time, and therefore the amount of 
fuel supplied from the common rail to the injector 10 can be reduced. That 
is to say, since the discharge amount of the fuel supply pump can be 
reduced, the size of the fuel pump can be made smaller. Further, even if 
the volume of the common rail is reduced, a high-efficiency injection 
apparatus can be obtained while maintaining pressure at a predetermined 
pressure. 
A second embodiment according to the present invention is described with 
respect to FIG. 5. 
According to the second embodiment, a pressure chamber 26 formed by an 
inner wall of a casing 61 and a pressure chamber formed by an inner wall 
of a valve casing 62 directly communicate with each other, thereby forming 
a control pressure chamber. The pressure chamber 63 is formed by a 
large-diameter chamber 63a, a medium-diameter chamber 63b, and a 
small-diameter chamber 63c disposed in this order from the bottom in FIG. 
5. 
A pressure control valve 70 is composed of a needle 71, a land portion 72, 
and a guide portion 73, and an armature 74 is fixed to an end portion of 
the guide portion 73. A notch 71a is formed axially in an outer peripheral 
wall of a cylindrical portion of the needle 71 which functions as a 
fluid-resistance portion. A seat portion 71b of the needle 71 seats on or 
unseats from a valve seat 62b provided on a junction portion between the 
large-diameter chamber 63a and medium-diameter chamber 63b, and a 
clearance between the outer peripheral wall of the needle 71 and an inner 
wall 62a of the valve casing 62, which forms the large-diameter chamber 
63a with the outer peripheral wall of the needle 71, made narrower than 
that of the first embodiment. The land portion 72 is slidable with an 
inner wall 62c of the valve casing 62 which forms the small-diameter 
chamber 63c. High-pressure fuel supplied from a common rail (not 
illustrated) is supplied to a fuel chamber formed around a tip end of a 
nozzle needle (not illustrated). Meanwhile fuel is supplied from a fuel 
passage 64 to the small-diameter chamber 63c, and further to the pressure 
chamber 26 through the large-diameter chamber 63a. 
When electric current to a coil 51 is switched on, the armature 74 is 
attracted toward the coil 51 by magnetic force generated by the coil 51, 
and the pressure control valve 70 is lifted together with the armature 74. 
Firstly, the land portion 72 slides to the inner wall 62c, and interrupts 
communication between the fuel passage 64 and medium-diameter chamber 63b. 
When the pressure control valve 70 is further lifted together with the 
armature 74, the volume of the pressure chamber 63 below the land portion 
72 increases, and the pressure of the pressure chamber 26 drops. Since the 
clearance between the outer peripheral wall of the valve body 71 and the 
inner wall 62a is narrow in this embodiment, lifting speed of the pressure 
control valve 70 is reduced to be less than that of the first embodiment 
by throttling the fuel passage with the narrow clearance. When the 
pressure control valve 70 is gradually lifted, pressure within the 
pressure chamber 26 also gradually drops. Then, the nozzle needle is 
gradually lifted, and fuel injection is started. For this reason, noise 
during the start of fuel injection is reduced, a rise of the injection 
rate in the beginning gets slower. Therefore, combustion in the combustion 
chamber gets slower and combustion noise as well as generation of nitrogen 
oxides can be restrained. 
When electric current to the coil 51 is switched off, the armature 74 is 
lowered, and the fuel passage 64 communicates with the pressure chamber 
26. At this time, fuel having been supplied from the fuel passage 64 is 
rapidly supplied to the pressure chamber 26 passing between the notch 71a 
and inner wall 62a, and pressure within the pressure chamber 26 also rises 
rapidly. Then, the nozzle needle is closed. 
Since the small-diameter chamber 63c is formed by providing a concave 
portion in the inner wall of the valve casing 62, not by the pressure 
control valve 70, sealing length in the axial direction of the guide 
portion 73 and valve casing 62 can be made longer. In this way, the static 
fuel amount which leaks toward the armature 74 from the clearance between 
the guide portion 73 and valve casing 62 can be reduced. 
Furthermore, according to the second embodiment, the pressure control valve 
70 is stopped by the valve body 71 being seated on the valve seat 62b, but 
the pressure control valve 70 can be stopped by the armature 74 contacting 
a stopper 53 before the valve body 71 seats on the valve seat 62b. 
A third embodiment according to the present invention is described with 
respect FIG. 6. 
A pressure chamber 84 formed by an inner wall of a valve casing 80 directly 
communicates with a pressure chamber 26, thereby forming a control 
pressure chamber. The pressure chamber 84 includes a large-diameter 
chamber 84a, a small-diameter chamber 84b, and a sliding hole 84c having a 
smaller diameter than the small-diameter chamber 84b, which are arranged 
in this order from the side of the pressure chamber 26. 
A pressure control valve 81 is composed of a valve body 82 and a guide 
portion 83 formed in a cylindrical shape, which are integrally formed. The 
valve body 82 is composed of a cylindrical portion 82a having a short 
axial length and a seat portion 82b formed in a tapered shape having a 
cross-section which is inclined inwardly in the radial direction, and is 
connected to a guide portion 83 by a connecting portion 83a formed in a 
tapered shape having a cross-section which is inclined inwardly in the 
radial direction toward the seat portion 82b. An outer peripheral wall of 
the cylindrical portion is slidable with an inner wall 80a of the valve 
casing 80, and the seat portion 82b seats on or unseats from a valve seat 
80b formed in an inner wall of the valve casing 80 at a junction portion 
between the small-diameter chamber 84b and sliding hole 84c. 
When electric current to a coil (not illustrated) is switched on, the 
pressure control valve 81 is lifted, and the cylindrical portion 82a 
slides with the inner wall 80a. In this way, communication between a fuel 
passage 85 to which fuel is supplied from a common rail and the pressure 
chamber 26 is interrupted. When the pressure control valve 81 is further 
lifted, volume of the large-diameter chamber 84a except for the pressure 
control valve 81 is increased, and thereby pressure of the pressure 
chamber 26 begins to drop. Accordingly, a nozzle needle (not illustrated) 
is lifted, and fuel injection is started. When the pressure control valve 
81 is lifted further, the seat portion 82b seats on the valve seat 80b. 
When electric current to the coil (not illustrated) is switched off, the 
pressure control valve 81 is lowered, and the fuel passage 85 communicates 
with the pressure chamber 26. Then, the pressure of the pressure chamber 
26 rises, and the nozzle needle is open. 
According to the third embodiment, since the valve body 82 functions both 
for opening and closing of the pressure control valve 81 and for 
regulating the pressure of the pressure chamber 26 and an additional land 
portion is not required separately from the valve body as in the second 
embodiment, the shape of the pressure control valve 81 is simplified. 
Furthermore, according to the present embodiment, the valve body can slide 
on the inner wall forming a sliding hole in which the guide portion slides 
by setting the outer diameters of the valve body being equal to that of 
the guide portion. In such a case, an upward moving distance of the 
pressure control valve is restricted by, for example, the stopper 53 
illustrated in FIG. 5. 
A fourth embodiment according to the present invention is described with 
respect to FIG. 7. 
A pressure chamber 93 formed by an inner wall of a valve casing 90 directly 
communicates with a pressure chamber 26, and thereby forming a control 
pressure chamber. The pressure chamber 93 has a small-diameter chamber 93b 
which is inclined inwardly in the radial direction from a large-diameter 
chamber 93a toward a sliding hole 93c in correspondence with the shape of 
a valve body 92 of a pressure control valve 91. High-pressure fuel from a 
common rail is supplied to the pressure chamber 93a through fuel passage 
94. 
When electric current to a coil (not illustrated) is switched on and the 
pressure control valve 91 is lifted, a clearance between an outer 
peripheral wall of the valve body 92 and an inner wall 90a forming the 
small-diameter chamber 93b is gradually throttled. Then, passage area 
formed between the outer peripheral wall of the valve body 92 and the 
inner wall 90a is reduced, and the clearance formed between the outer 
peripheral wall of the valve body 92 and the inner wall 90a functions as a 
fluid-resistance portion. That is to say, fuel which is supplied from the 
fuel passage 94 so as to fill the increased volume by the lifting movement 
of the pressure control valve 91 cannot keep up with the lifting speed of 
the pressure control valve 91 due to the fluid-resistance portion. As the 
same result with the increase in the volume of the pressure chamber 93, 
and pressure of the pressure chamber 26 drops. Then, a nozzle needle is 
open, and fuel injection is started. When the pressure control valve 91 is 
further lifted, the valve body 92 seats on a valve seat 90b. 
According to the fourth embodiment, since the clearance formed between the 
outer peripheral wall of the valve body 92 and the inner wall 90a 
gradually gets narrower as the pressure control valve 91 is lifted, the 
passage is gradually throttled, and a rise of the injection rate in the 
beginning can get slower. Therefore, combustion in the combustion chamber 
gets slower and combustion noise as well as generation of nitrogen oxides 
can be restrained. 
Furthermore, according to the fourth embodiment, and lifting of the 
pressure control valve 91 is stopped by the valve body 92 seating on the 
valve seat 90b, but it is acceptable that a pressure control valve 91 
being stopped by a tapered surface of a valve body contacting with an 
inner wall for forming a small-diameter chamber. 
A fifth embodiment according to the present invention is described with 
respect to FIG. 8. 
A pressure chamber 105 formed by an inner wall of a valve casing 100 
directly communicates with a pressure chamber 26 through a communication 
hole 107, and thereby forming a control pressure chamber. A sliding hole 
106 is formed above the pressure chamber 105. 
A pressure control valve 101 is composed of a valve body 102 which is 
downwardly narrowed, a guide portion 103 which slides on an inner wall 
100a forming a sliding hole 106, and a connecting portion 104 of a 
diameter smaller than the guide portion 103 which connects the valve body 
102 with the guide portion 103, which are integrally joined. An outer 
diameter of the valve body 102 is equal to an outer diameter of the guide 
portion 103. A tip portion 102a of the valve body 102 is formed in a 
conical shape, and seats on or unseat from a valve seat 108 formed in the 
valve casing 100. A guide portion 102b disposed on the side of the 
connecting portion 104 of the valve body 102 slides with the inner wall 
100a. 
When electric current to a coil (not illustrated) is switched on and the 
pressure control valve 101 is lifted, an outer peripheral wall of the 
guide portion 102a of the valve body 102 slides with the inner wall 100as, 
and communication between the pressure chamber 105 and a fuel passage 109 
to which fuel is supplied from a common rail is interrupted. When the 
pressure control valve 101 is lifted further, volume of the pressure 
chamber 105 except for the pressure control valve 101 is increased, and 
pressure of a pressure chamber 26 begins to drop. Then, a nozzle needle 
(not illustrated) is lifted, and fuel injection is started. When the 
pressure control valve 101 is lifted further, an armature (not 
illustrated) which is lifted together with the pressure control valve 101 
contacts with a stopper (not illustrated), and lifting of the pressure 
control valve 101 is stopped. 
When electric current to the coil (not illustrated) is switched off, the 
pressure control valve 101 begins to be lowered, the fuel passage 109 
communicates with the pressure chamber 105, and a nozzle needle is open. 
The pressure control valve 101 is stopped by the valve body 102 seating on 
the valve seat 108. 
According to the fifth embodiment, since the outer diameters of the valve 
body 102 is equal to that of the guide portion 103, it is easy to 
manufacture the valve casing 100. Furthermore, since the armature and the 
pressure control valve 101 can be corporated into the valve casing 100 
from the upper side in FIG. 8 while these two parts are assembled 
together, it is possible to assemble easily and to simplify the assembling 
work. 
A sixth embodiment according to the present invention is described with 
respect to FIGS. 9 and 10. 
As shown in FIG. 9, a nozzle valve composed of a needle 120 and a stopper 
112 is disposed in a sliding hole provided in an axial direction of a 
casing member 111. The stopper 112 is composed of a retainer 113 and a rod 
114, and opposes the nozzle needle 120 so as to form a clearance in the 
axial direction. For this reason, even if the nozzle needle 120 is lifted 
rapidly when the nozzle needle 120 is open, the nozzle needle 120 is 
stopped by a tip of the rod 114. As shown in FIG. 10, the retainer 113 
formed in a disk shape is provided with notches 113a at each side face. 
A retainer 121 for a compression coil spring 123 is provided on the nozzle 
needle 120 at the side of stopper 112, and a pin 122 with which the 
compression coil spring 123 engages is provided on an upper-end surface of 
the retainer 121. This pin 122 opposes the rod 114. 
Fuel within a pressure chamber 115 is enclosed by a guide portion 120a of 
the nozzle needle 120 which slides with an inner wall of the casing member 
111, and a control pressure chamber which includes the pressure chamber 
115 is formed between a land portion 42 and the guide portion 120a. That 
is to say, the guide portion 120a of the nozzle needle 120 functions as a 
piston. According to this structure, urging force of the compression coil 
spring 123 which urges the nozzle needle 120 in the valve-closing 
direction is not adjusted in accordance with a difference in 
cross-sectional surface areas of a piston and the nozzle needle as in the 
first embodiment and it is possible to design in consideration of only the 
cross-sectional area of the nozzle needle 120. 
According to the sixth embodiment, overall length of an injector 110 can be 
shortened to nearly half in comparison with the first embodiment by the 
nozzle needle 120 functioning as a piston. Moreover, there is no need to 
form a fuel passage to return leaked fuel within the casing member 111 to 
a fuel tank, thereby the manufacturing process be simplified. 
Additionally, since the stopper 112 opposes the nozzle needle 112 so as to 
form a clearance in the axial direction, useless volume in a needle spring 
chamber 116 can be reduced. 
FIG. 11 illustrates a modification of the sixth embodiment. FIG. 11 
illustrates a sectional view of a retainer 131 in the same position as in 
FIG. 10. Grooves 132 are formed in the retainer 131 in the axial direction 
of the retainer at opposing 180.degree. angles, and a round-shaped concave 
portion 133 is formed in a central portion. Fluid can pass through 
passages formed by the grooves 132. 
The present invention has been described in connection with what are 
presently considered to be the most practical preferred embodiments. 
However, the present invention is not meant to be limited to the disclosed 
embodiments, but rather is intended to include all modifications and 
alternative arrangements included within the spirit and scope of the 
appended claims.