Fuel injection nozzle

A fuel injection nozzle of the present invention has an accumulating chamber in a body in which high pressure fuel fed from the fuel injection pump is stored using a non-return valve. A needle valve is arranged in the body to inject the fuel in the accumulating chamber. A nozzle needle of the needle valve and a valve member are arranged coaxially and in series with each other. Those end portions of the nozzle needle and valve member which are adjacent to each other are slidably and liquid-sealingly fitted together to define a damping chamber between the valve member and the nozzle needle. Further, a damping plunger is coaxially fitted into the valve member. A passage which connects the damping chamber with the side of the fuel injection pump is coaxially formed in the damping plunger and has a reduced area.

BACKGROUND OF THE INVENTION 
The present invention relates to a fuel injection nozzle for injecting 
highly-pressurized fuel into the combustion chamber in the internal 
combustion engine such as a diesel engine. 
The fuel injection nozzle of this type was disclosed in U.S. Pat. No. 
4,349,152 and Japanese Patent Disclosure No. 85,433/85. These well-known 
fuel injection nozzles are provided with accumulating chambers defined in 
their bodies, into which highly-pressurized fuel fed from the fuel 
injection pumps is introduced. When the highly-pressurized fuel is 
introduced into the accumulating chamber, pressure in the valve chamber of 
the body which is communicated with the accumulating chamber is also 
raised. Therefore, the nozzle needle is lifted by this pressure in the 
valve chamber and fuel in the accumulating and valve chambers is thus 
injected through the injection hole. 
In the case of these above-described fuel injection nozzles of the pressure 
accumulation type, however, the fuel injection is attained using the 
accumulated energy of fuel filled in the accumulating chamber. Therefore, 
pressure in the accumulating chamber is maximum at the start of the fuel 
injection, then lowers gradually, and is minimum at the end of the fuel 
injection. In other words, the nozzle needle opens the injection hole to 
the maximum degree at the start of the fuel injection and then gradually 
makes it smaller. As a result, fuel injection ratio is maximum at the 
start of the fuel injection, and then gradually decreases toward the end 
of the fuel injection. Combustion pressure in the combustion chamber rises 
rapidly to thereby increase combustion sound and engine noise. In 
addition, temperature in the combustion chamber rises rapidly to thereby 
increase the amount of NO.sub.x generated. 
SUMMARY OF THE INVENTION 
The present invention is therefore intended to eliminate the 
above-described drawbacks and the object of the present invention is to 
provide a fuel injection nozzle capable of increasing the fuel injection 
ratio at the end of the fuel injection than at the start thereof to reduce 
engine noise and restrain NO.sub.x from being generated. 
The object of the present invention can be achieved by a fuel injection 
nozzle according to the present invention. The fuel injection nozzle of 
the present invention is provided with a body, in which an accumulating 
chamber which can be communicated with the discharge side of a fuel 
injection pump is defined. The fuel injection nozzle comprises a 
non-return valve means for shutting off the communication between the 
discharge side of the fuel injection pump and the accumulating chamber to 
store fuel, which is supplied from the fuel injection pump and which has 
certain pressure and quantity, in the accumulating chamber. The non-return 
valve includes a valve member movable along the axis of the body. The 
valve member has a connector hole at one end thereof which is usually 
connected with the discharge side of the fuel injection pump. The fuel 
injection nozzle further comprises a needle valve means for injecting fuel 
in the accumulating chamber into the combustion chamber of the engine. The 
needle valve means includes a nozzle needle arranged coaxially and in 
series with the valve member. Either the other end of the valve member or 
one end of the nozzle needle is slidable and liquid-tightly fitted into 
the other for defining a damping chamber between the two end portions of 
the nozzle needle and valve member. A damping plunger is coaxially fitted 
into the valve member in the manner that it can abut the nozzle needle and 
it is urged toward the nozzle needle. A through-hole which communicates 
the damping chamber with the connector hole is formed in the damping 
plunger and has a reduced area. 
According to the above-described fuel injection nozzle, the damping chamber 
is defined between the valve member and the nozzle needle. Therefore, as 
the nozzle needle is lifted by pressure in the accumulating chamber at the 
start of fuel injection, pressure in the damping chamber is raised 
accordingly because the volume of the damping chamber is reduced. This 
pressure rise in the damping chamber acts to restrain the lift of the 
nozzle needle. As a result, the opening degree of the needle valve remains 
small at the start of the fuel injection even if the pressure in the 
accumulating chamber is high, thereby enabling the fuel injection ratio to 
be reduced. As the fuel injection comes nearer to its end, fuel in the 
damping chamber escapes into the connector hole through the through-hole 
and reduced area to thereby reduce the pressure gradually in the damping 
chamber. As the pressure in the damping chamber is reduced, however, the 
nozzle needle is lifted accordingly to further reduce the volume of the 
damping chamber, so that a sudden fall of pressure in the damping chamber 
can be prevented. The nozzle needle is quickly lifted after a 
predetermined delay time from the start of fuel injection to increase the 
opening degree of the needle valve, thereby enabling the fuel injection 
ratio to increase at the end of fuel injection rather than at the start 
thereof. Therefore, the amount of NO.sub.x generated as well as engine 
noise can be reduced due to the characteristic of the fuel injection ratio 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a first example of the fuel injection nozzle according to the 
present invention. The fuel injection valve 10 is connected to a fuel 
injection pump 12 through a fuel pipe 14. The fuel injection pump 12 is of 
a well-known in-line or distributor type. The fuel injection pump 12 is 
driven by an engine (not shown) to feed a predetermined amount of fuel 
from a fuel tank 16 to the fuel injection nozzle 10 for a predetermined 
time period in response to the number of engine rotation. 
The fuel injection nozzle 10 is provided with a holder and nozzle bodies 18 
and 20 which are coaxially connected with each other through a retaining 
nut 22. An accumulating chamber 24 is defined in the holder body 18. The 
accumulating chamber 24 can be connected to the fuel pipe 14 through a 
suction passage 26 which is coaxially formed in the holder body 18. On the 
other hand, the accumulating chamber 24 is also communicated with a valve 
chamber 28 in the nozzle body 20 through a passage 15 which is formed in 
the nozzle body 20. 
Plural injection holes 30 are arranged at the foremost end of the nozzle 
body 20 and can be communicated with the valve chamber 28. The injection 
holes 30 are open and closed by contacting and separating a needle seat 34 
of a nozzle needle 32 relative to a body seat 36 of the nozzle body 20. 
The nozzle needle 32 is slidably fitted into a guide hole 38 which is 
coaxially formed in the nozzle body 20, and the upper end of the nozzle 
needle 32 is projected into the accumulating chamber 24. 
A check valve 40 is housed in the accumulating chamber 24. The check valve 
40 has a column-like valve member 42 extending coaxial to the holder body 
18. The upper portion of the valve member 42 is formed as a large-diameter 
portion 44, whose upper end surface is defined as a valve seat 46. A 
pressure spring 50 is arranged between the large-diameter portion 44 of 
the valve member 42 and a flange portion 48 on the upper end of the nozzle 
needle 32. The valve member 42 is urged against the ceiling of the 
accumulating chamber 24 by means of the pressure spring 50. The 
communication between the suction passage 26 and the accumulating chamber 
24 is shut off under this state. On the other hand, the nozzle needle 32 
is also urged against the body seat 36 at the needle seat 34 thereof by 
means of the pressure spring 50, thereby keeping the injection holes 30 
closed. 
The lower end portion of the valve member 42 is slidably inserted into a 
blind hole 52 which is coaxially formed in the upper portion of the nozzle 
needle 32. A damping chamber 54 is thus defined in the blind hole 52 by 
means of the lower end surface of the valve member 42. A damping plunger 
56 is coaxially fitted into the valve member 42 to move along the axis of 
the valve member 42. A through-hole 58 having a small diameter is 
coaxially formed in the damping plunger 56, passing through the damping 
plunger 56. This through-hole 58 communicates the damping chamber 54 with 
a connector hole 60 which is formed in the upper end portion of the valve 
member 42 and which has a diameter larger than that of the damping plunger 
56. The damping plunger 56 is urged by a spring 64 housed in the connector 
hole 60. The damping plunger 56 is thus held contacted with a lower end 
face 66 of the connector hole 60 at the flange portion 62 thereof. A 
reduced area 68 is formed in the middle of the through-hole 58 in the 
damping plunger 56. The lower end portion of the damping plunger 56 is 
formed as a small-diameter portion 70 and the upper end of this 
small-diameter portion 70 is formed as a spill lead 72. A spill hole 74 
which is communicated with the accumulating chamber 24 is formed in the 
valve member 42 in the radial direction thereof. This spill hole 74 
co-operates with the spill lead 72 to establish and shut off the 
communication between the accumulating chamber 24 and the damping chamber 
54. 
The above-described first example of the fuel injection nozzle 10 will be 
described on its operation, referring to a timing chart shown in FIG. 2. 
When high pressure fuel is fed from the fuel injection pump 12 to the fuel 
injection nozzle 10, it is introduced into the connector hole 60 through 
the suction passage 26. The flange portion 62 of the damping plunger 56 is 
urged against the lower end face 66 of the connector hole 60 by the high 
pressure fuel introduced into the connector hole 60. On the other hand, 
the high pressure fuel in the connector hole 60 flows into the damping 
chamber 54 through the throughhole 58. When the damping chamber 54 is 
filled with the high pressure fuel, pressure Pc in the connector hole 60 
rises and the valve member 42 of the check valve 40 is lifted at a point A 
in FIG. 2 against the pressure spring 50, thereby causing the check valve 
40 to be opened. Since the suction passage 26 is thus communicated with 
the accumulating chamber 24, the high pressure fuel fed from the fuel 
injection pump 12 flows into the accumulating chamber 24 as well as the 
connector hole 60. Pressure Pacc in the accumulating chamber 24 is thus 
raised. 
When the valve member 42 is lifted, the volume of the damping chamber 54 is 
reduced and pressure Pd in the damping chamber 54 is thus raised rapidly 
at a point B in FIG. 2. The damping plunger 56 is therefore lifted by the 
pressure Pd in the damping chamber 54 against the spring 64. Since the 
pressure Pd in the damping chamber 54 gradually escapes into the connector 
hole 60 through the through-hole 58 and reduced-area 68 in the damping 
plunger 56, it then reduces at a point C in FIG. 2. The damping plunger 56 
is thus lowered by the spring 64. 
When the supply of high pressure fuel into the accumulating chamber 24 
continues from the point A at which the check valve 40 is open, the 
pressure Pacc in the accumulating chamber 24 rises higher. When fuel 
delivery from the fuel injection pump 12 is completed, pressure in the 
fuel pipe 14 is relieved on the side of the fuel injection pump 12. 
Therefore, pressures Pc and Pacc in the connector hole 60 and accumulating 
chamber 24 reduces at a point D in FIG. 2 and the valve member 42 of the 
check valve 40 is thus forced to abut the ceiling of the accumulating 
chamber 24 at the point D by means of the pressure spring 50. Therefore, 
the check valve 40 is closed at a point E in FIG. 2 to shut off the 
communication between the suction passage 26 and the accumulating chamber 
24. After the check valve 40 is closed, the pressure Pacc in the 
accumulating chamber 24 is prevented from escaping on the side of the pump 
12. However, the pressure Pc in the connector hole 60 is allowed to escape 
on the side of the pump 12 even after the point E. 
Since the volume of the damping chamber 54 is increased by the valve member 
42 lifted, the pressure Pd in the damping chamber 54 is quickly lowered 
from a point F in FIG. 2. 
It will be taken into consideration how the nozzle needle 32 which is under 
the pressure of fuel in the valve chamber 28 is moved, the valve chamber 
28 being communicated with the accumulating chamber 24 and following any 
pressure change in the accumulating chamber 24. When the valve member 42 
starts rising from the point D, the pressure spring 50 is extended to 
thereby reduce its urging force, and when the pressure Pd in the damping 
chamber 54 is rapidly decreased, as described above, from the point D, the 
force which pushes down the nozzle needle 32 is also rapidly reduced. 
Therefore, the nozzle needle 32 begins to lift from the point D. As a 
result, the needle seat 34 of the nozzle needle 32 is separated from the 
body seat 36 to open the injection holes 30. Therefore, fuel injection 
through these fuel injection holes 30 is started at the point D. 
When the nozzle needle 32 is thereafter lifted to reduce the volume of the 
damping chamber 54, the pressure Pd in the damping chamber 54 is again 
raised until the point E. The rise of the nozzle needle 32 is thus 
restrained during the time period starting from the point E and ending in 
the point F in FIG. 2. 
The pressure Pd in the damping chamber 54 begins to decrease from the point 
F in FIG. 2 because fuel in the damping chamber 54 escapes on the side of 
the pump 12 through the through-hole 58, reduced-area 68 and connector 
hole 60. Therefore, the force which restricts the lifting of the nozzle 
needle 32 is reduced, the nozzle needle 32 is lifted faster, widening the 
gap between the needle and body seat 34 and 36 to increase the amount of 
fuel injected through the injection holes 30. 
When the bottom of the damping chamber 54 in the nozzle needle 32 is 
abutted on the lower end of the damping plunger 56 at a point G in FIG. 2, 
the spring 64 further acts as a force which restrains the lifting of the 
nozzle needle 32. However, fuel pressure in the accumulating chamber 24 or 
valve chamber 28 also acts on the nozzle needle 32. The nozzle needle 32 
is therefore lifted together with the damping plunger 56 against the 
spring 64. The gap between the needle seat 34 of the nozzle needle 32 and 
the body seat 36 is made larger to further increase the amount of fuel 
injected through the injection holes 30. 
When the nozzle needle 32 continues to lift together with the damping 
plunger 56, the spill lead 72 of the damping plunger 56 opens the spill 
port 74 at a point H in FIG. 2, the fuel in the accumulating chamber 24 
flows into the damper chamber 54. Therefore, fuel pressure in the 
accumulating chamber 24 is decreased, while the pressure Pd in the damping 
chamber 54 is raised. Therefore, the pressure in the valve chamber 28 
which is communicated with the accumulating chamber 24 is balanced to the 
pressure in the damping chamber 54 and the nozzle needle 32 is quickly 
lowered by the pressure spring 50. Thus, the needle seat 34 of the nozzle 
needle 32 contacts the body seat 36 to close the injection holes 30 at a 
point I in FIG. 2, thereby completing the fuel injection. 
According to the above-described example the characteristic of injection 
ratio follows the lifting movement of the nozzle needle 32, as shown in 
FIG. 2. In other words, the injection ratio is small at the start of 
injection but then gradually becomes greater. 
Static balance in the nozzle needle 32 at the time when the nozzle needle 
32 is lifted is represented as follows: 
##EQU1## 
wherein F.sub.SD represents a set load of the pressure spring 50, d.sub.c 
an effective outer diameter of the valve member 42, d.sub.S a seat 
diameter of the nozzle needle 32, Pacc a pressure in the accumulating 
chamber 24 and Pd a pressure in the damping chamber 54. 
Therefore, the force which acts to lift the nozzle needle 32 or nozzle 
opening pressure Po in the accumulating chamber 24 is as follows: 
##EQU2## 
On the contrary, the force which acts on the nozzle needle 32 in the axial 
direction at the time when the nozzle 10 is closed becomes as follows: 
##EQU3## 
because Pacc=Pd. Therefore, the urging force F.sub.SD of the pressure 
spring 50 (or F.sub.SD =spring constant.times.amount of the nozzle needle 
lifted) is only left to act as a force to the nozzle needle 32. The nozzle 
needle 32 is thus strongly pushed down so that the nozzle 10 can be 
instantaneously closed, thereby improving the cutoff of the fuel 
injection. 
FIG. 3 shows a second example of the fuel injection nozzle according to the 
present invention. The second example is different from the first one 
shown in FIG. 1 in that a pressure spring 80 for the nozzle needle 32 is 
arranged independently of a spring 82 for the valve member 42, and that 
the nozzle needle 32 is guided by a guide hole 38 in the nozzle body 20 
and by the hollow portion of the valve member 42. In FIG. 3, numeral 86 
represents a stopper wall for the springs 80 and 82, and numeral 84 
represents a cap. Other parts in FIG. 3 are represented by the same 
reference numerals as those in FIG. 1, and a description on these parts 
will be omitted. 
According to the second example, the nozzle needle 32 and valve member 42 
are urged by their respective springs 80 and 82. Therefore, their set 
loads can be independently determined. More specifically, the nozzle 
opening pressure can be determined by the load which is set on the 
pressure spring 80, and the amount of the nozzle needle 32 lifted is set 
by the amount of the moved damping plunger 56. The valve member opening 
pressure of the check valve can be determined by the load which is set on 
the spring 82, and the amount of the valve member 42 lifted is set by the 
position of the valve member 42 which abuts the stopper wall 86. 
Static balance in the nozzle needle 32 at the time of opening the nozzle 10 
is represented as follows: 
##EQU4## 
wherein d.sub.G represents an outer diameter of a guide rod portion for 
the nozzle needle 32. 
Therefore, the nozzle opening pressure Po is as follows: 
##EQU5## 
The example shown in FIG. 3 can achieve the same operation as that of the 
one shown in FIG. 2, but the former is different from the latter in that 
the nozzle opening can be attained simultaneously at the check valve 
opening. More specifically, when the valve member 42 starts to move toward 
the closing direction and the pressure in the damping chamber 54 begins to 
reduce, the nozzle needle 32 is lifted against the pressure spring 80 to 
thereby open the injection holes 30 at the same time. Since the pressure 
in the damping chamber 54 rises following the lifting of the nozzle needle 
32, the nozzle needle 32 is slowly lifted so that the injection ratio is 
small at the start of the fuel injection. Thereafter, the operation of the 
second example until the fuel injection is completed is the same as that 
of the first one shown in FIG. 1.