Fuel injection valve

A fuel injection valve for an internal combustion engine, in which a lift-limiting plunger is slidably fitted in a plunger chamber to receive fuel pressure for limiting the lifting amount of a nozzle needle. A back pressure chamber is defined by an end face of the plunger remote from the nozzle needle as part of the plunger chamber. A selector valve is controlled by an electronic control unit to establish communication between the back pressure chamber and a fuel intake passageway during low speed/low load operation of the engine, whereby the nozzle needle is lifted through a limited stroke to obtain a reduced fuel injection rate as well as a prolonged fuel injection period. A pressure inlet chamber permanently communicates with the back pressure chamber and is selectively communicated with the fuel intake passageway and disconnected therefrom by the selector valve, in synchronism with selective establishment and interruption of communication between the back pressure chamber and the fuel intake passageway. An accumulator is slidably fitted within an accumulator chamber communicating with the pressure inlet chamber and liftable in a direction away from the pressure inlet chamber against the force of a return spring with an increase in the pressure within the latter chamber. Thus, a reduction in the fuel injection quantity caused by the limitation of the needle lift can be compensated for.

BACKGROUND OF THE INVENTION 
This invention relates to a fuel injection valve for use in internal 
combustion engines, and more particularly to a fuel injection valve of 
this kind which has a reduced nozzle needle lift during low speed/low load 
operation of the engine such as idling. 
A diesel engine in general is provided with fuel injection valves with 
their nozzle tips projected into respective cylinders of the engine to 
inject fuel delivered from a fuel injection pump into the respective 
cylinders in an intermittent manner. Conventionally, automatic injection 
valves are employed in most diesel engines, which are constructed such 
that when the pressure of pressurized fuel delivered from a fuel injection 
pump surpasses the setting load of a nozzle spring urging a nozzle needle 
in its closing diretion, the nozzle needle is lifted by the pressurized 
fuel so that the fuel is injected into an engine cylinder. 
However, according to such conventional construction, it is difficult to 
control both the fuel injection rate and the fuel injection period to 
respective different values according to operating conditions of the 
engine, particularly, between during low speed/low load operation of the 
engine such as idling and during normal operation of same. Further, in the 
conventional automatic injection valves, the nozzle needle is lifted 
through a constant stroke over all operating conditions of the engine. As 
a result, the conventional construction has the disadvantage that during 
low speed/low load operation of the engine such as idling fuel injection 
takes place over a very short period of time and at a high injection rate, 
causes large combustion noise in the engine. 
To overcome this disadvantage, a fuel injection valve has been proposed, 
e.g. by Japanese Provisional Utility Model Publication No. 59-62273, which 
comprises a main body having injection holes formed in its tip and a fuel 
intake passageway formed therein and communicating with the injection 
holes, a nozzle needle slidably fitted within the main body for 
alternately closing and opening the injection holes, a lift-limiting 
plunger slidably fitted in a plunger chamber defined within the main body 
and having an end face remote from the nozzle needle disposed as a 
pressure-receiving surface to receive fuel pressure for limiting the 
lifting amount of the nozzle needle, and a selector valve disposed to 
selectively establish or interrupt communication between a back pressure 
chamber defined by the end face of the plunger remote from the nozzle 
needle as part of the plunger chamber and the above-mentioned fuel intake 
passageway. During low speed/low load operation of the engine, the 
selector valve is controlled to establish communication between the back 
pressure chamber and the fuel intake passageway, whereby the the nozzle 
needle is lifted through a limited or reduced stroke to obtain a reduced 
fuel injection rate as well as a prolonged fuel injection period. 
According to this proposed fuel injection valve, by virtue of the limited 
lifting stroke of the nozzle needle the opening area of the injection 
holes is kept at a moderate small value to obtain a reduced injection 
quantity, that is, a lower fuel injection rate and a longer injection 
period, even when the pressurized fuel from the fuel injection pump has 
high pressure, thereby mitigating engine combustion noise during low 
speed/low load operation of the engine such as idling. 
However, according to the proposed fuel injection valve, if during needle 
lift-limited operation a pumping plunger of the fuel injection pump is 
operated through the same effective delivery stroke as that executed by a 
plunger of a conventional ordinary type fuel injection valve incapable of 
limiting the lifting amount of the nozzle needle, the actual quantity of 
fuel injected into the engine cylinder decreases by an amount 
corresponding to the amount of throttling the injection holes by the 
limited stroke of the nozzle needle, resulting in reduced engine output. 
One way to prevent such engine output reduction would be to set a control 
sleeve of the fuel injection pump to a position where the effective 
delivery stroke of the nozzle needle is increased during needle 
lift-limited operation so as to compensate for a reduction in the fuel 
injection quantity caused by limiting the lifting amount. However, this 
requires returning the control sleeve to a normal position when the engine 
enters a normal operating region, which in turn requires a complicate 
control mechanism as well as a complicate manner of operating the 
mechanism. Besides, it is also difficult to smoothly change the effective 
delivery stroke of the pumping plunger at changeover from needle 
lift-limited operation to needle lift-unlimited operation or vice versa. 
SUMMARY OF THE INVENTION 
It is the object of the invention to provide a fuel injection valve which 
is capable of reducing combusion noise of the engine during low speed/low 
load operation and which is provided with a means of simple construction 
for compensating for a reduction in the fuel injection quantity caused by 
limiting the nozzle needle lift without changing the effective delivery 
stroke of the pumping plunger of the fuel injection pump. 
The present invention provides a fuel injection valve for an internal 
combustion engine, which comprises a main body having injection holes 
formed in its tip and a fuel intake passageway formed therein and 
communicating with the injection holes, a nozzle needle slidably fitted 
within the main body for alternately closing and opening the injection 
holes, a lift-limiting plunger slidably fitted in a plunger chamber 
defined within the main body and having an end face remote from the nozzle 
needle disposed as a pressure-receiving surface to receive fuel pressure 
for limiting the lifting amount of the nozzle needle, a selector valve 
disposed to selectively establish or interrupt communication between a 
back pressure chamber defined by the end face of the plunger remote from 
the nozzle needle as part of the plunger chamber and the above-mentioned 
fuel intake passageway, and control means for controlling the selector 
valve in dependence on operating conditions of the engine. When the engine 
is operating in a predetermined low speed/low load condition such as 
idling, the selector valve is controlled by the control means to establish 
communication between the back pressure chamber and the fuel intake 
passageway, whereby the the nozzle needle is lifted through a limited or 
reduced stroke to obtain a reduced fuel injection rate as well as a 
prolonged fuel injection period. 
The fuel injection valve according to the invention is characterized by 
comprising: a pressure inlet chamber permanently communicating with the 
back pressure chamber and disposed to be selectively communicated with the 
fuel intake passageway and disconnected therefrom by the selector valve, 
in synchronism with the selective establishment and interruption of 
communication between the back pressure chamber and the fuel intake 
passageway; an accumulator chamber communicating with the pressure inlet 
chamber; an accumulator slidably fitted within the accumulator chamber and 
liftable in a direction away from the pressure inlet chamber with an 
increase in the pressure within the pressure inlet chamber; and urging 
means urging the accumulator in a direction toward the pressure inlet 
chamber against lifting of the accumulator. 
The above and other objects, features and advantages of the invention will 
be more apparent from the ensuing detailed description taken in 
conjunction with the accompanying drawing.

DETAILED DESCRIPTION 
The invention will now be described in detail with reference to the drawing 
showing an embodiment thereof. In the figure, reference numeral 1 
designates a fuel injection nozzle, on a lower end of which is mounted a 
nozzle body 3 and fastened thereto by means of a retaining nut 5 
threadedly fitted on the nozzle 1, via a distance piece 4. The nozzle 
holder 2 is formed therein with a plunger chamber 6 and an enlarged spring 
chamber 7, both extending along the axis of the nozzle holder 2 and 
continous with each other with an annular stepped shoulder 8 therebetween. 
A lower end of the spring chamber 7 opens in a lower end face of the 
nozzle holder 2 in alignment with an upper open end of a tapered hole 9 
having a lower side smaller in diameter than an upper side thereof and 
having a lower open end in alignment, via a small axial hole 10, with an 
upper open end of a needle guide bore 11 formed in the nozzle body 3. The 
nozzle holder 2 has an enlarged head portion 2a at an upper portion 
thereof, which is formed therein with a transversely extending valve 
chamber 12. An upper open end of the plunger chamber 6 opens into the 
valve chamber 12 at an axially intermediate portion thereof at right 
angles thereto in a fashion forming a T-shaped intersection together with 
the chamber 12. A lift-limiting plunger 13, which is a so-called "central 
plunger", has an enlarged portion 13a slidably fitted within the plunger 
chamber 6, for limiting the lifting amount of a nozzle needle 14, 
hereinafter referred to. The enlarged portion 13a of the plunger 13 
extends upwardly from an axially intermediate portion of the plunger, from 
lower end face of which downwardly extends a reduced-diameter portion 13b 
into the spring chamber 7. The nozzle needle 14 is slidably fitted in the 
needle guide bore 11 formed in the nozzle body 3, and has an upper end 
face 14a provided with an upwardly extending reduced-diameter journal 14b 
supporting thereon a movable spring seat 15. A nozzle spring 17 formed of 
a coiled spring is interposed tautly between the movable spring seat 15 
and a stationary spring seat 16 affixed to an upper end wall of the spring 
chamber 7 defining the stepped shoulder 8. The nozzle needle 14 is 
disposed to be biased in a lower extreme or seated position by the nozzle 
spring 17, with its valve seating portion 14c seated on a valve seat 3a 
formed in the nozzle body 3, thus keeping the injection holes 3b closed, 
when no injection is effected. In this needle-seated position, a whole 
lifting gap Ll is provided between the upper end face 14a of the nozzle 
needle 14 and a lower end face of the distance piece 4. On the other hand, 
the lift-limiting plunger 13 is biased in a lower extreme position due to 
its own gravity, wherein an initial lifting gap L2 is provided between a 
lower end face of the reduced-diameter portion 13b and an opposed upper 
end face of a central projection 15a on an upper end face of the movable 
spring seat 15. 
A back pressure chamber 6a is defined in an upper end portion of the 
plunger chamber 6 between an upper end face of the lift-limiting plunger 
13 and a border plane between the plunger chamber 6 and the valve chamber 
12. An accumulator chamber 18 is defined in the nozzle holder 2 and 
disposed opposite the back pressure chamber 6a with respect to the valve 
chamber 12 interposed therebetween, and has its lower open end opening 
into an axially intermediate portion of the valve chamber 12 at right 
angles thereto in a fashion forming a T-shaped inter-section together with 
the chamber 12. An accumulator 19, in the form of a piston, is slidably 
fitted in the accumulator chamber 18 and urged downward by a return spring 
20 formed of a coiled spring accommodated in the chamber 18. As described 
later, the accumulator 19 acts to compensate for a reduction in the fuel 
injection quantity caused by limiting the lifting amount of the nozzle 
needle 14. A pressure inlet chamber 18a forming part of the chamber 18 is 
defined between a lower end face of the accumulator 19 and a border plane 
between the accumulator chamber 18 and the valve chamber 12 and in 
permanent communication with the back pressure chamber 6a by way of a 
communication passage 33 formed in the nozzle holder 2 along an inner 
peripheral surface of the valve chamber 12, indicated by the chain line in 
the figure. The pressure inlet chamber 18a is disposed in axial alignment 
with the back pressure chamber 6a. A selector valve 21 formed of a spool 
valve is slidably fitted within the valve chamber 12 for movement through 
a predetermined stroke. The selector valve 21 has an annular groove 21a 
formed in its outer peripheral surface near its one end and at a location 
registrable with a fuel intake passageway formed by a fuel intake passage 
24 and a fuel inlet port 25, both hereinafter referred to. The valve 21 is 
urgedly biased by a return spring 22 formed of a coiled spring arranged at 
the opposite end, to a left extreme position as indicated by the solid 
lines in the figure, wherein the back pressure chamber 6a and the 
accumulator chamber 18 are disconnected from the fuel intake passageway 
24, 25 by the selector valve 21, while when the selector valve 21 is in 
the opposite right extreme position as indicated by the broken lines, the 
back pressure chamber 6a and the accumulator chamber 18 are both 
communicated with the fuel intake passage 24 by way of the annular groove 
21a. The selector valve 21 is selectively shifted between the above two 
extreme positions, by a solenoid 23 arranged around the opposite end of 
the selector valve 21 and electrically connected to an electronic control 
unit 30 by lead wires 23a and 23b. The control unit 30 is responsive to 
operating conditions of the engine, not shown, and supplies a driving 
signal to the solenoid 23 when the engine is operating in a predetermined 
low speed/low load region such as an idling region, to energize the 
solenoid 23 so that the selector valve 21 is shifted to the right extreme 
position against the force of the return spring 22. On the other hand, 
when the engine is operating in a normal operating region other than the 
predetermined low speed/low load region, the control unit 30 deenergizes 
the solenoid 23 to allow the selector valve 21 to be returned to the left 
extreme position by the force of the return spring 22. 
The fuel intake passage 24 communicates between the fuel inlet port 25 
formed in an upper surface of the nozzle holder 2 and a pressure chamber 
26 defined within the nozzle body 3, and is formed of a first through hole 
24a formed in the nozzle holder 2, a second through hole 24b formed in the 
distance piece 43, and a third through hole 24c formed in the nozzle body 
3. The first through hole 24a has its upper end so located as to 
permanently communicate with the fuel inlet port 25 via the annular groove 
21a in the selector valve 21 both when the selector valve 21 assumes the 
left extreme position and when it assumes the right extreme position. The 
fuel inlet port 25 is to be connected to a discharge port of a fuel 
injection pump 31. The nozzle needle 14 has its pressure-receiving surface 
14d located within the pressure chamber 26 formed in the nozzle body 3. 
In the figure, reference numerals 27 and 28 designate drain ports to be 
connected to a fuel tank 32 or a like lower pressure zone for returning 
leak fuel thereto from the valve chamber 12 and the accumulator chamber 
18, respectively, and 29 a leak fuel passage formed along the axis of the 
spool 21. 
The operation of the fuel injection valve according to the invention will 
now be described. 
When the engine is operating in the predetermined low speed/low load 
region, the control unit 30 causes the solenoid 23 to be energized to 
force the selector valve 21 to be moved to the right extreme position 
against the force of the return spring 22 as indicated by the broken lines 
so that the back pressure chamber 6a and the pressure inlet chamber 18a of 
the accumulator chamber 18 are communicated with the fuel intake 
passageway 24, 25 via the annular groove 21a of the selector valve 21. In 
this position, pressurized fuel from the fuel injection pump 31 is guided 
through the fuel inlet port 25 and then along the annular groove 21a of 
the selector valve 21, part of which fuel flows into the back pressure 
chamber 6a and the pressure inlet chamber 18a whereby the lift-limiting 
plunger 13 is downwardly urged by the pressurized fuel in the chamber 6a 
to thereby restrict the lifting amount of the nozzle needle 14, and the 
accumulator 19 is urgedly displaced upward against the force of the return 
spring 20 into a position as indicated by the broken lines in the figure. 
On the other hand, the remainder of the pressurized fuel delivered to the 
annular groove 21a is further guided through the fuel intake passage 24, 
i.e. the first through third passages 24a-24c into the pressure chamber 
26. When the pressure within the pressure chamber 26 thus rises to a 
predetermined initial valve opening pressure, the nozzle needle 14 is 
lifted through the initial lift L2 so that the injection holes 3b are 
opened to a substantially small opening to cause fuel injection through 
the injection holes 3b. On this occasion, even if the pressure within the 
pressure chamber 26, i.e. the pressure of pressurized fuel from the fuel 
injection pump exceeds the initial valve opening pressure, the nozzle 
needle 14 is prevented from further lifting beyond the initial lift L2 
since the fuel pressure within the back pressure chamber 6a downwardly 
urges the lift-limiting plunger 13 at its upper end face, thereby 
maintaining the opening area of the injection holes 3b at the 
substantially small value. Thus, the fuel injection rate is maintained at 
a low value and the fuel injection period is made longer. 
When the pressure delivery of fuel by the fuel pumping plunger of the fuel 
injection pump 31 terminates, the supply of fuel to the fuel inlet port 25 
is accordingly interrupted. However, even then the fuel pressure within 
the pressure inlet chamber 18a is transmitted to the pressure chamber 26 
through the annular groove 21a and the fuel intake passage 24 to act upon 
the chamber 26, whereby the nozzle needle 14 is held open to cause 
continued injection of fuel from the pressure inlet chamber 18a through 
the injection holes 3b, to thereby compensate for a reduction in the fuel 
injection quantity caused by limitation of the lifting amount of the 
nozzle needle 14. 
After the injection of fuel from the pressure inlet chamber 18a has been 
completed, the accumulator 19 is returned by the force of the return 
spring 20 to the original position as indicated by the solid lines, and at 
the same time the nozzle needle 14 is downwardly forced by the force of 
the nozzle spring 17 to the position where the nozzle needle has its valve 
seat 14c seated on the valve seat 3a to close the injection holes 3b. 
On the other hand, when the engine is operating in a normal operating 
region other than the predetermined low speed/low load operating region, 
the control unit 30 deenergizes the solenoid 23 to allow the selector 
valve 21 to be moved to and held at the left extreme position as indicated 
by the solid lines in the figure by the force of the return spring 22, 
whereby the back pressure chamber 6a and the pressure inlet chamber 18a of 
the accumulator chamber 18 are both disconnected from the fuel intake 
passageway 24, 25 so that neither of the lift-limiting plunger 13 nor the 
accumulator 19 is acted upon by fuel pressure to bring about a lift 
limitation-released state. Consequently, all the pressurized fuel from the 
fuel injection pump 31 is guided through the fuel inlet port 25, annular 
groove 21a, and fuel intake passage 24 into the pressure chamber 26. When 
the pressure within the pressure chamber 26 reaches the predetermined 
initial valve opening pressure, the nozzle needle 14 is lifted against the 
force of the nozzle spring 17 to execute the initial lift L2 whereby the 
injection holes 3b are opened to a substantially small opening. With a 
further increase in the pressure within the pressure chamber 26, the 
nozzle needle 14 is further lifted together with the lift-limiting plunger 
13 against the force of the nozzle spring 17 to execute the whole lift Ll 
whereby the injection holes 3b are opened to the maximum opening to obtain 
a high fuel injection rate and a short fuel injection period. 
When the lift-limiting plunger 13 has been lifted as noted above, the 
residual fuel within the back pressure chamber 6a flows into the pressure 
inlet chamber 18a to forcibly displace the accumulator 19 upward stroke 
against the force of the spring 20. Therefore, in this high fuel injection 
rate mode, the fuel injection is effected in two steps such that the 
nozzle needle 14 is lifted through the initial lift L2 against the force 
of the nozzle spring 17, and then further lifted until the whole lift Ll 
is executed, against the combined force of the nozzle spring 17 and the 
return spring 20. 
After completion of the fuel injection, termination of the pressure 
delivery of the pumping plunger of the fuel injection pump causes 
interruption of fuel supply to the fuel inlet port 25, lowering the 
pressure within the pressure chamber 26 so that the lift-limiting plunger 
13 and the nozzle needle 14 descend, respectively, by its own gravity and 
by the force of the nozzle spring 17, to thereby close the injection holes 
3b. 
Although in the embodiment described above the selector valve 21 is driven 
by the solenoid 23, this is not limitative, but a selector valve 
responsive to delivery fuel pressure from the fuel injection pump may be 
employed instead. Further alternatively may be employed a selector valve 
responsive to load on the engine or rotation of the engine.