Diesel engine fuel injection system

The diesel internal combustion engine fuel injection system includes an accumulator nozzle having its opening pressure close to its closing pressure so as to provide a high turn down ratio without excessive maximum charging pressure. The accumulator nozzle may include a displacement piston which is used to lower the charging pressure by a fixed amount after the injection of fuel into the engine cylinder commences. Alternatively, the accumulator nozzle may include a small moveable piston which serves to raise the closing pressure after the injection of fuel into the engine cylinder commences.

BACKGROUND OF THE INVENTION 
This invention relates to a fuel injection system for a diesel internal 
combustion engine, and more particularly, to a diesel engine fuel 
injection system that utilizes accumulator nozzles, to inject diesel fuel 
into the engine cylinders and that employs a multiple pumping element or 
chamber jerk pump for providing the system with pressurized diesel fuel. 
Jerk pump fuel injection systems for diesel engines are known. In such 
systems, each engine cylinder has its own pumping element. An inlet or 
fill port allows the inflow of fuel to the pumping chamber of the pump. 
Before ingress into the pumping chamber, the fuel is stored in a fuel 
gallery and is pre-pressurized, to about 50 psi, by a separate charging 
pump. 
When the pressure of the fuel in the pumping chamber of the jerk pump is 
high enough, the pump's delivery valve opens and fuel passes into an 
injection line. The high pressure fuel from the pumping chamber presses 
against the fuel in the injection line causing a compressive wave to 
propagate down the injection line at a velocity of sound in fuel 
(approximately 5,000 feet per second). 
A nozzle or ejector unit is located at the other end of the injection line, 
and in essence, closes that end of the line. The initial part of the 
compressive wave may be reflected at the nozzle back down the injection 
line toward the pump. The compressive wave pressure quickly builds up to a 
pressure required to open the nozzle. The open nozzle injects fuel into 
the engine combustion chamber through tiny orifices. Much of the fuel 
driven toward the nozzle by the compressive wave is injected into the 
engine combustion chamber in this manner. The match among the injection 
line internal diameter, the total nozzle orifice area and the pressure of 
the compressive wave determines the fraction of fuel that is reflected 
during the injection. 
Referring back to the jerk pump, the pumping piston completes its mission 
by opening its spill port. As a result, fuel is dumped from the pumping 
chamber back into the fuel gallery. As the pressure in the pumping chamber 
drops, the delivery valve closes to prevent a back flow from the injection 
line. The compressive wave is no longer formed, and this lack of pressure 
is propagated to the nozzle, also at the speed of sound. When the pressure 
drops, the nozzle closes, ending the injection of fuel into the engine 
cylinder. 
The function of the delivery valve in such fuel injection systems is 
important and complex. If the delivery valve were a "pure" check valve, 
those parts of the compressive wave that were reflected at the nozzle 
would be reflected again at the delivery valve. If this second reflection 
was strong enough, it could open the nozzle again when it arrives there. 
This "secondary" injection would occur too late to contribute to engine 
power but in time to partially burn. Such a late burn wastes fuel and 
forms excessive smoke even by standards existent before the recent 
emphasis on pollution control. 
To prevent such a secondary injection, delivery valves generally include 
structure that permits a fixed amount of fuel to be by-passed back into 
the pumping chamber before the delivery valve is allowed to seal. As a 
result, the residual pressure in the injection line is brought close to 
zero between injections. It has been recognized that there are perhaps 
more disadvantages to the use of a delivery valve than advantages; yet 
their usage continues. 
The time of the injection of fuel into the engine cylinders controls the 
timing of the heat release as the fuel burns. Before control of emissions 
became so important, the fuel was injected generally twenty degrees before 
the engine piston reached its top dead center. Pressure and temperature in 
the engine chamber is rapidly rising at this time, and fuel would have its 
combustion delayed until just before top dead center. As the cycle 
preceded past top dead center, the heat release was very fast, creating 
high pressures and temperatures at the peak of the stroke. Oxides of 
nitrogen ("NOx") were formed rapidly under these conditions, and even 
though the fuel had a relatively long time to burn, there was also 
significant smoke and particulates produced. 
It is known that substantial reductions in NOx pollutants can be achieved, 
without much penalty in fuel consumption, if the timing is retarded to 
approximately five degrees before top dead center. However, such timing is 
now "on the edge". In other words, a little more retarding and the fuel 
consumption goes up quickly; a little less retarding, and the NOx 
pollution goes up quickly. 
Because of the hydraulics of the jerk pump system, there is a natural 
retarding as the engine speed increases. This is caused by the fixed time 
that it takes for the pressure wave to travel down the injection line. 
Hence, to maintain optimal timing at all engine speeds, the current 
practice is to use timing devices such as, for example, of the type 
generally described in Berman and DeLuca, FUEL INJECTION AND CONTROLS FOR 
INTERNAL COMBUSTION ENGINES (Simmons-Boardman Publishing Corporation, 
1962) at pages 166-168 ("Berman"). Others have, however, suggested 
electronically timed injection to optimize conditions for both engine load 
and speed. 
Control of pollutants caused by the operation of diesel engines has and 
continues to be an important motivating factor in designing fuel injection 
systems for diesel engines. Pollutants fall into two general classes: one 
is the NOx's caused by allowing the combustion chamber's temperature to be 
too high for too long; and the other is in the form of smoke, 
particulates, carbon monoxide and odor that are formed by incomplete 
combustion. As noted above, the control of the timing of the fuel 
injection has been a primary means utilized to control NOx pollutants, 
with the conventional wisdom being that the later the start of the fuel 
injection, the lower the NOx pollutants. Unfortunately, later injection 
timing tends to decrease engine efficiency and to increase the other class 
of pollutants. 
Under most conditions of steady state diesel engine combustion, there is 
plenty of air to burn the fuel. Incomplete combustion is caused by the 
fuel not vaporizing in time or the fuel vapor not getting mixed with the 
air in time. In the short time that combustion takes place, the smallest 
drops of fuel easily vaporize and complete their combustion. However, 
relatively larger drops take longer to complete this process, and it is 
these larger drops, particularly those formed by the low pressure end of 
the injection, that cause smoke, odor, carbon monoxide and particulate 
pollutants. In other words, it is only a small part of the injected fuel 
that leads the "incomplete combustion" class of pollutants. 
From the standpoint of fuel injection system design, it has long been 
recognized that the larger drops of fuel are formed only when the pressure 
drop across the nozzle orifices is small. In the conventional jerk pump 
injection system, the latter condition exists as the nozzle needle valve 
attempts to close the orifices, that is, at the end of the injection 
cycle. 
One proposed way of avoiding ending the injection with a low pressure drop 
is to raise the closing pressure at the nozzles. This has been done 
experimentally by applying a hydraulic back pressure to the nozzle needle 
valve from an external high pressure hydraulic source. This does minimize, 
to a certain extent, the incomplete combustion class of pollutants, but it 
is not practical in a working fuel injection system. More specifically, if 
the closing pressure is raised in a conventional system, the opening 
pressure is also raised and at cranking speeds, the injection pump cannot 
raise the pressure of the fuel sufficiently high. 
It has been proposed to use accumulator nozzles to inject the fuel in the 
engine cylinders since such nozzles can be employed to avoid low pressure 
injection. In an accumulator nozzle, the fuel injection starts at full 
charging pressure. The nozzle injection pressure drops continuously until 
it reaches the nozzle closing pressure. The nozzle closes at that pressure 
such that at no time is fuel injected at a lower pressure. Accordingly, 
the use of accumulator nozzles with a conventional fuel injection system 
should theoretically yield less smoke, particulates, carbon monoxide, and 
odor than do other conventional nozzles. Unfortunately, the accumulator 
nozzle has opening pressure limitations during engine cranking like those 
of conventional nozzles. 
The use of an accumulator nozzle also has other possible advantages in that 
it allows a simple method of timing the injection as compared with other 
conventional injection nozzles. Specifically, the accumulator nozzle does 
not inject while its accumulator volume is being charged. The injection 
starts only when the pressure in the injection line is reduced. This can 
be delayed after the charging is complete without difficulty. For example, 
if the charging pump completes its charging function and is then isolated 
from the injection line by, for example, a simple check valve, the 
injection line pressure can thereafter be reduced by a secondary or spill 
valve at a time not related to the charging process. If this secondary 
valve is controlled electronically, all the flexibility of electronic 
timing can be used to also reduce the other pollutants, that is, the 
NOx's. Alternatively, the secondary valve may be controlled mechanically 
by a timing device which is dependent on engine speed and which will 
advance the injection at higher speeds to obtain an optimum 
pollutants/fuel consumption relationship. 
Because of the evident advantages of accumulator nozzles in diesel engine 
fuel injection systems, those working in the art have attempted to solve 
the opening pressure limitations during engine cranking noted above. In 
this regard and as noted, it has long been recognized that the final 
injection pressure should be as high as possible. This, of course, can be 
accomplished by raising the closing pressure of the accumulator nozzle. 
Although the conventional jerk pumps have no difficulty in supplying high 
pressure fuel under normal operating conditions, such pumps, as noted, are 
often not able to supply high pressure while the engine is cranking. If 
the closing pressure is held constant, it is limited by the requirement 
that the fuel injection system be able to start the engine under all 
conditions. In this regard, it has been recognized that the closing 
pressure may be very low, under engine starting conditions, and may be 
raised to a higher value, under engine running conditions, by imposing a 
back pressure in the chamber whose pressure controls the opening of the 
nozzle needle valve of the accumulator nozzle. This can be done by 
regulating the pressure of the sump into which the timing or secondary 
valve spills. Under this arrangement, the back pressure would be 
approximately zero while the engine was being cranked because there would 
not be enough spill flow to raise the pressure. After the engine is 
running for a short time, the back pressure in the chamber will rise. 
Thus, the opening pressure (and closing pressure) can be very low for easy 
starting and the closing pressure can thereafter be raised to a higher 
value for reduced incomplete combustion pollutants under running 
condition. 
There is, however, one serious problem that has long been recognized with 
regard to the use of accumulator nozzles in diesel engine fuel injection 
systems and that, as a practical matter, has prevented the usage of 
accumulator nozzles (as opposed to more complicated and expensive injector 
units that include accumulator nozzles as a component part) in such 
systems. Specifically, the accumulator nozzle that can deliver a certain 
maximum fuel charge or quantity of fuel has difficulty delivering a small 
enough charge or quantity to allow the engine to idle satisfactorily. The 
quantity of fuel discharged may be given by the following relationship: 
EQU q=V/K(P.sub.1 -P.sub.2) 
Where "q" is equal to the discharged quantity in cubic millimeters; "V" is 
equal to the volume of the accumulator in cubic millimeters; "K" is equal 
to the bulk modulus of fuel, for example 280,000 psi; "P.sub.1 " is equal 
to the peak accumulator pressure in psi; and "P.sub.2 " is equal to the 
nozzle closing pressure in psi. 
The ratio of the maximum fuel charge delivered to the minimum fuel charge 
delivered is called the "turn down ratio." The art has recognized that 
engines need a turn down ratio of at least 8 and preferably 10. 
The injected quantity fuel is stored in the compressibility of the fuel in 
the accumulator volume. As already stated, the quantity of fuel delivered 
is proportional to the pressure difference between the starting pressure 
and the closing pressure. The minimum delivery occurs when the charging 
pressure P.sub.1 is just enough to open the nozzle, that is, just greater 
than the opening pressure. The minimum delivery is proportional to the 
opening and closing pressure difference, e.g., 1,000 to 1,500 psi. To 
obtain a turn down ratio of 8, the maximum charging pressure, P.sub.2, 
would have to be 8,000 to 12,000 psi higher than the closing pressure. 
This is quite demanding of a jerk pump. In addition, raising the closing 
pressure of the accumulator nozzle aggravates the turn down ratio problem. 
In accumulator nozzles raising the closing pressure raises the opening 
pressure even more. The larger difference in these pressures would force 
extremely high maximum charging pressures at full delivery to obtain a 
reasonable turn down ratio. Such higher pressures would require extra 
expense, reduced life of the hydraulic equipment, and wasted power. 
SUMMARY OF THE INVENTION 
The present invention affords, for the first time, a practical, economical 
solution to the problem that has long confronted those working in the art 
and that has heretofore prevented the adoption and use of accumulator 
nozzles in diesel engine fuel injection systems even though, as noted, 
such usage would otherwise be quite advantageous in assisting to control 
the formation of the so-called incomplete combustion class of pollutants. 
This solution is relatively simple, straightforward and inexpensive as 
compared to other proposed solutions that require high pressures, complex 
expensive systems and system components. 
Specifically, the present invention permits accumulator nozzles of the 
present invention to be used in jerk pump diesel engine fuel injection 
systems and to achieve high turn down ratios, that is, in excess of ten, 
while having their opening pressures close to their closing pressures and 
without requiring excessively high maximum charging pressure. The improved 
accumulator nozzle of the present invention includes a displacement piston 
that is adapted to lower the pressure of the fuel in the nozzle's 
accumulator chamber by a preselected amount after the nozzle needle valve 
is first opened so as to permit fuel to be injected through the orifices. 
Alternatively, the improved accumulator nozzle includes a piston moveable 
in response to the difference in the fuel pressures in the accumulator 
chamber and the chamber which controls the opening of the nozzle needle 
valve, with this moveable piston being adapted to raise the closing 
pressure of the accumulator nozzle a preselected amount after the nozzle 
needle valve is first opened so as to permit fuel to be injected through 
the orifices. 
Accordingly, it is a principal object of the present invention to provide 
an improved fuel injection system for a diesel internal combustion engine 
where the system utilizes improved accumulator nozzles that are able to 
achieve high turn down ratios. A related object of the present invention 
is to provide an improved diesel engine fuel injection system of the type 
described where the improved accumulator nozzles utilized in that system 
have their opening pressures close to their closing pressures so as to 
provide a high turn down ratio without requiring an excessive maximum 
charging pressures. 
Another object of the present invention is to provide an improved diesel 
engine fuel injection system of the type described where the improved 
accumulator nozzles utilized with that system each includes a displacement 
piston which serves to lower the charge pressure by preselected amount 
after the injection of fuel commences. A related object of the present 
invention is to provide an improved diesel engine fuel injection system of 
the type described where alternatively, each of the improved accumulator 
nozzles utilized with that system includes a small, moveable piston that 
raises the closing pressure after the injection of fuel commences. 
Still another object of the present invention is to provide an improved 
diesel engine fuel injection system of the type described where the system 
includes a source of diesel engine fuel; a pump for pumping fuel under 
pressure to each of the diesel engine cylinders; a plurality of injection 
lines, one for each of the diesel engine cylinders, a plurality of 
improved accumulator nozzles, one for each of the diesel engine cylinders, 
with one of the injection lines providing a fluid connection between the 
outlet of the pump and the inlet of one of the accumulator nozzles and 
with each of the accumulator nozzles including novel structure that 
permits the accumulator nozzles to have their opening pressures close to 
their closing pressures so as to achieve high turn down ratios without 
having an excessive maximum charging pressures; a sump for receiving fuel 
from each of the spill lines of the accumulator nozzles, including a 
regulator for imposing a back pressure on each of the spill lines, which 
back pressure is low under engine cranking conditions and is high under 
engine operating conditions; a plurality of secondary valves, one disposed 
in each of the injection lines, with each secondary valve being 
selectively operable to provide a fluid connection between an outlet of 
the pump and the inlet of the accumulator nozzle or to place the spill 
line of the accumulator nozzle in fluid connection with the pressure 
regulated sump; and a controller for selectively moving the secondary 
valves between their two positions so that the accumulator nozzles will 
have low opening pressures during engine cracking and will have high 
closing pressures under normal operating conditions. 
A related object of the present invention is to provide an improved diesel 
engine fuel injection system of the type described where the pump includes 
a plurality of pumping elements, one for each of the diesel engine 
cylinders. A further related object is to provide an improved diesel 
engine fuel injection system of the type described where a displacement 
piston is disposed in each of the accumulator nozzles and in fluid 
communication with the accumulator chamber, with the displacement piston 
being adapted to lower the charge pressure of the accumulator chamber of 
its accumulator nozzle by a preselected amount after the accumulator 
nozzle has commenced injecting fuel under pressure through its orifices. 
Still another related object of the present invention is to provide an 
improved diesel engine fuel injection system of the type described where 
alternatively, a piston is movable in response to the difference in the 
fuel pressures in the accumulator chamber and in the chamber that serves 
to bias the nozzle needle valve of the accumulator nozzle to its closed 
position, with the movable piston being adapted to raise the closing 
pressure of the accumulator nozzle after the nozzle needle valve is moved 
to the position whereby the injection of fuel through the orifices of the 
accumulator nozzles commences. 
Yet another object of the present invention is to provide an improved 
accumulator nozzle for use in a diesel engine fuel injection system of the 
type described where the improved accumulator nozzle includes novel 
structure for permitting the opening pressure of the accumulator nozzle to 
be close to its closing pressure so as to provide a high turn down ratio 
without having an excessive maximum charging pressure. A related object of 
the present invention is to provide an improved accumulator nozzle of the 
type described where the accumulator nozzle includes a displacement piston 
disposed in fluid connection with the accumulator chamber of the 
accumulator nozzle, with the displacement piston being adapted to lower 
the charge pressure of the accumulator chamber by a preselected amount 
after the accumulator nozzle has commenced injecting fuel through its 
orifices. Another related object of the present invention is to provide an 
improved accumulator nozzle of the type described where the accumulator 
nozzle includes, alternatively, a piston movable in response to the 
differences in the fuel pressures in the accumulator chamber and the 
chamber that serves to bias the nozzle needle valve to its closed 
position, with the movable piston being adapted to raise the closing 
pressure of the accumulator nozzle by a preselected amount after the 
accumulator nozzle has begun injecting fuel through the orifices of the 
accumulator nozzle. 
These and other objects, advantages and aspects of the present invention 
will be more fully understood with reference to the following description 
of the preferred embodiments of the present invention, as described in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The improved fuel injection system of the present invention is for use with 
a conventional diesel internal combustion engine, as for example, one 
having four cylinders. Referring now to FIG. 1, four cylinders 12, 14, 16 
and 18 of such an engine is shown, partially and schematically, at 22. 
Accumulator nozzles 24, 26, 28 and 32 are mounted in and operatively 
associated with the engine cylinders 12, 14, 16 and 18, respectively, so 
that the accumulator nozzles may inject diesel fuel into its associated 
engine cylinder. Each of the accumulator nozzles 24, 26, 28 and 32, and 
the subassembly that cooperate with the accumulator nozzle to accomplish 
the desired injection of fuel therefrom, are functionally and structurally 
identical. Accordingly, only one accumulator nozzle, nozzle 24, and its 
subassembly 33, will be described therein, it being understood that the 
nozzles 26, 28 and 32 and their individual subassemblies, are the same 
except as hereinafter specifically noted. 
The inlet 34 of the accumulator nozzle 24 is in fluid connection with the 
downstream end 36 of an injection line 38. The upstream end 42 of the 
injection line 38 is in fluid connection with a conventional check valve 
44 as, for example, a coil spring biased ball check valve. The check valve 
is, in turn, in fluid connection with the outlet or discharge port 46 of a 
conventional jerk pump 48. 
The pump 48 includes four pumping elements or chambers, one for each of the 
nozzles 24, 26, 28 and 32. A chamber 54 is associated with the nozzle 24 
and includes a cylinder wall 53 having at least one inlet or fill port 54 
in the chamber wall through which fuel may be drawn into the pumping 
chamber 52 of the jerk pump. The chamber 52 also has at least one spill 
port, now shown, although one port may serve both the fuel "fill" and 
"spill" function as is covered and uncovered by a plunger or piston 55 
that reciprocally moves in the chamber in a conventional manner. The 
metering system in a jerk pump may use a land on the plunger 55 to cover 
and uncover the fill and spill ports. Usually the two ports are slightly 
displaced from each other. The effective length of the land on the plunger 
determines the quantity of fuel pumped. The plunger may include a helical 
cut along its surface such that in different angular orientations, the 
length of the exposed land is different. By controlling the orientation, 
metering of fuel quantity is effected. Such a metering system is described 
on page 23, and especially of FIG. 32 of Burman's book. 
A conventional fuel gallery 56 serves as a supply of filtered diesel engine 
fuel, under a pressure of around 50 psi, for the chamber 52 of the jerk 
pump 48. The gallery 56 may also serve as the common fuel supply for the 
other pumping elements associated with the nozzles 24, 26, 28 and 32. 
Fuel in or in fluid connection with the injection line 38 may be dumped 
into a sump 57 that may be used in common by the subassemblies of the 
other accumulator nozzles 26, 28 and 30. A branch or secondary line 58 
interconnects the injection line 38 with the sump 57. A secondary or dump 
valve 62 is disposed within this secondary line 58 and is of a 
conventional structure and function. Specifically, the secondary valve 62 
may be moved between a first position where fuel under pressure from the 
jerk pump 48 passes through the check valve 44, the injection line 38, and 
into the inlet 34 of the accumulator nozzle 24 and second position where 
the injection line 38 is in fluid connection with the sump 57 so that fuel 
in that injection line, as well as the fuel in the secondary line 58 and 
those parts of the accumulator nozzle 24 which are in fluid connection 
with the interior of the injection line 38, may flow into the sump. 
A controller 64 selectively controls the operation of the secondary valve 
62--and additionally the secondary valves that are a part of the 
subassemblies of the other accumulator nozzles 26, 28 and 32--so that it 
will be moved between its first to second position to promote proper 
timing and operation of the engine 22 in accordance with conventional 
engine operation techniques. This controller 64 may be a simple mechanical 
device, or it may be a sophisticated electronic digital device such as, 
for example, the Model EEC IV marketed by the Electrical & Electronics 
Division of the Ford Motor Company. The latter is a microprocessor based 
device that is capable of receiving signals from sensors sensing engine 
speed and angular position of the pistons, of determining the precise time 
a given nozzle should be fired and of sending signals to solenoid valves. 
Specifically, the operation of the valve 62 is controlled so that fuel is 
injected through the accumulator nozzle 24 into the engine cylinder 12 at 
the proper time before the engine piston reaches its top dead center so as 
to minimize the formation of NOx pollutants while promoting the efficient 
and economical operation of the engine 22. 
A conventional back pressure regulator 66 is in fluid connection with the 
sump 57 and controls the pressure of the sump and of the fuel passing into 
the sump through the secondary line 58 and the injection line 38. The use 
of the regulator 66 permits the accumulator nozzle to have a low opening 
pressure while the engine 22 is being cranked, and to have a high closing 
pressure under normal engine operating conditions. 
The structure of the first preferred embodiment of the accumulator nozzle 
24--and thus the accumulator nozzles 26, 28 and 32--is best illustrated in 
FIG. 2. As noted above, the embodiment of the accumulator nozzle 24 shown 
in FIG. 2 is one of two of the preferred embodiments of the improved 
accumulator nozzle of the present invention. 
More specifically and with reference with FIG. 2, accumulator nozzle 24 
includes a body 68 that has an inlet 34 at one end 72. As noted above, the 
inlet 34 is in fluid connection with the downstream end 36 of the 
injection line 38. The inlet 34 permits fuel under pressure to flow from 
the injection line 38 into a accumulator chamber 74. A check valve 76 is 
located downstream from the inlet 34 and prevents fuel from flowing from 
the accumulator chamber 74 back into the injection line 38. 
A plurality of small orifices 78 are formed in the other end 82 of the 
accumulator nozzle 24. They are of conventional design and arrangement. 
The other end 82 is adapted to project into the interior of the diesel 
engine cylinder 12 and the orifices 78 are used inject or spray drops of 
fuel into the interior of the engine cylinder 22 for combustion therein in 
a conventional manner. 
A second chamber 84 is formed within the other end 82 immediately upstream 
from the orifices 78. A fluid passage 85 provides a fluid connection 
between the accumulator chamber 74 and the second chamber 84 so that in 
all material respects, the pressure of the fuel in the accumulator chamber 
74 and the pressure of the fuel in the second chamber 84 are the same. 
An annular valve seat 86 is formed in the end of the second chamber 84 
adjacent to the orifices 78. A first valving end 88 of a nozzle needle 
valve 92 is adapted to be seated in this seat 86 and when seated, to block 
or prevent the flow of fuel through the orifices 78. Specifically, the 
first end 88 of the nozzle needle valve 92 is shaped so that when it is 
seated in the valve seat 86, flow of fuel through the nozzles or orifices 
78 is prevented. 
The nozzle needle valve 92 is generally cylindrical in shape and the 
diameter of the first end 88 is less than the diameter of the central 
portion 96 which is adapted to specifically move within the bore 98 in the 
other end 82. The tolerances between the bore 98 and the central portion 
96 are such that to prevent leakage of fuel therebetween. The fuel under 
pressure in the second chamber 84 acts on the nozzle needle valve, in 
particularly, the larger diameter central portion 96 thereof to bias or 
urge the valve 92 away from the position wherein its first end 88 is 
seated in the seat 86. 
A third chamber 102 is formed in the body 68 between the accumulator 
chamber 74 and the second chamber 84. This third chamber is generally 
cylindrical in shape and has a first end 104 and a second end 106. There 
is no fluid connection between the third chamber 102 and either of the 
other chambers 74 and 84, although the bore 98 communicates with the 
chamber 102 and the second end 94 of the nozzle needle valve 92 extends 
into that chamber even when first end 88 is seated on the seat 86. 
A spring retainer 108 is mounted on the second end 94 of the nozzle needle 
valve and receives one end of a coil compression spring 112. The other end 
of the coil compression spring 112 abuts the second end 106 of the chamber 
102. The spring force of the coil compression spring 112 is selected so 
that spring will bias the nozzle needle valve 92 toward the position 
wherein its first end 88 is seated against the seat 86 whenever the fuel 
pressure in the second chamber 84 drops below the closing pressure. 
A spill passage 114 is formed in the body 68, and extends from the third 
chamber 102. It provides a fluid connection between that chamber 102 and 
the injection line 38, at a point upstream from the check valve 76. 
A bore 116 extends between the second end 106 of the third chamber 102 and 
the end 118 of the accumulator chamber 74. A moveable piston 122 is 
adapted to reciprocally move within the bore 116. The piston includes a 
central portion 124 that is disposed within this bore 116, a first end 126 
and a second end 128. The dimensions and tolerances of the central portion 
124 and the bore 116 are selected so that there is no fluid connection 
between the chambers 74 and 102. The first end 126 of the piston 122 is 
disposed Within the third chamber 102 while the second end 128 of the 
piston 122 is disposed within the chamber 74. The first end 126 has a 
larger diameter than the central portion 124, and the second end 128 
terminates in an enlarged portion 132 which serves as a spring retainer. A 
coil compression spring 134 extends between the retainer 132 and the end 
118 of the chamber 74 and serves to bias the retainer 132, and thus the 
piston 122, away from the end 118. 
As noted, the piston 122 is axially moveable within the bore 116 and is 
coaxial with the nozzle needle valve 92. When the moveable piston 122 is a 
first position, the proximal portion 135 of the first end 126 abuts the 
end 106 of the chamber 102 and the distal portion 136 is spaced from the 
second end 94, including the retainer cap 108, of the nozzle needle valve 
92. When the moveable piston 122 is moved to a second position, due to the 
existence of a pressure differential between the chambers 74 and 102, the 
distal portion 136 of the first end 126 of the piston 122 abuts the second 
end 94 of the nozzle needle valve 92 and exerts a force thereon 
proportional to the pressure differential (minus, of course, the force 
exerted by the spring 134). The spring 112, as well as the differences in 
the diameters of the first end 126 and the second end 128, are selected so 
that the force of the spring 112, as well as the force exerted by the 
moveable piston 122, will urge or bias the nozzle needle valve 92 to the 
position shown in FIG. 2 (where the first end 88 of the valve is seated in 
the seat 86) whenever the fuel pressure in the accumulator chamber 74 
exceeds the fuel pressure in the third chamber 102 by a preselected 
amount. 
The embodiment of the accumulator nozzle 24 illustrated in FIG. 2 and 
described hereinabove functions in a conventional manner except as 
hereinafter noted. Specifically, during engine operation, the chamber 52 
of the jerk pump 48 pumps fuel under pressure to the accumulator nozzle 24 
through the injection line 38 while the valve 62 is in a position blocking 
a fluid connection between that injection line 38 and the sump 57. Fuel 
under pressure is introduced into the accumulator chamber 74 through the 
inlet 34 and the check valve 76. Fuel under pressure also is introduced 
into the second and third chambers 84 and 102 through the passages 85 and 
114, respectively. Because the pressures in the chamber 74, 84 and 102 are 
identical, the first end 88 of the nozzle needle valve 92 is and remains 
seated, under the bias of the spring 112, in the seat 86 thereby 
preventing the flow of fuel through the orifices 78. Similarly, the 
moveable piston 122 remains in its first position under the bias of the 
spring 134 so that the proximal end 135 of the first end 126 abuts the end 
106 of the third chamber. 
Under the continued pumping action of the pumping element of the pump 48, 
the pressure in the chambers 74, 84 and 102 continues to increase. When 
the piston 55 reaches its spill port, the pumping action ceases, the 
pressure in the chamber 52 decreases, and the check valve 44 isolates the 
injection line 38 from the chamber 52. The controller 64 then actuates the 
secondary valve 62 so that that valve is positioned whereby fluid 
communication occurs between the injection line 38 and the sump 57. (The 
valve 62 may be actuated at or after the end of the pumping stroke of the 
pump 48.) When the valve 62 is actuated, the accumulator nozzle 24 will 
"fire", that is, will permit the injection of fuel into the cylinder 12; 
provided, of course, that the pressure in the chambers 74 and 84 are above 
the opening pressure of the nozzle 24. (This opening pressure is 
determined by the spring force of the spring 112, together with the 
pressure if any remaining in the third chamber 102 which, as noted above, 
is in fluid communication with the injection line 38, the secondary line 
58 and thus the sump 57.) The opening pressure may be raised in accordance 
with the back pressure imposed upon this chamber 102 by the back pressure 
regulator 66. 
Assuming, however, that the charging pressure in the accumulator chamber 74 
is above the opening pressure of the nozzle 24, the nozzle needle valve 92 
will be moved away from the seat 86 due to the pressure of the fuel in the 
second chamber 84. The amount of fuel injected by the accumulator nozzle 
24 is determined by the difference between the charging pressure and the 
closing pressure. The minimum quality of fuel injected is obtained when 
the charging pressure is just enough to open the nozzle 24. The maximum 
injected quantity is obtained when the charge pressure is at its maximum 
value. As noted above, this maximum injected quantity or delivery is 
proportional to the difference between the maximum charging pressure and 
the closing pressure. Likewise, the minimum delivery is proportional to 
the difference between the opening pressure and the closing pressure. 
The opening pressure in a conventional accumulator nozzle is substantially 
higher (more than 1,000 psi) than its closing pressure because the 
injection fuel presses on a smaller area to open the nozzle than it does 
to hold it open. In order to obtain an adequate turn down ratio in such a 
conventional nozzle, it was necessary that the difference between the 
maximum charging pressure and the closing pressure be several times, 
perhaps eight, the difference between the opening and closing pressures. 
This requirement led to excessive or very high, e.g., 15,000 to 20,000 
psi, maximum charging pressures. Such excessive maximum charging pressures 
required extra expense, reduced the life of the hydraulic equipment, and 
wasted power. 
The embodiment of the present invention, described in connection with FIG. 
2, solves this problem by raising the closing pressure to be close to the 
opening pressure. Specifically, the moveable piston 122 is moved, as a 
result of the differential in the pressures in the chambers 74 and 102 
after the nozzle 24 has been fired, so that its distal portion 136 abuts 
and presses on the end 94 of the nozzle needle valve 92 immediately after 
the nozzle needle valve starts to open. This abutment tends to increase 
the closing pressure by a preselected amount. The diameter of the moveable 
piston may be selected to make this increase in the closing pressure as 
large as desired. With this increase in the closing pressure, the minimum 
fuel quantity injected may be very small. Accordingly, the turn down ratio 
can be very large with even modest maximum charging pressures. 
Moreover, because the pressure in the third chamber 102 "holds" both the 
nozzle needle valve 92 and the moveable piston 122 in their "rest" 
positions, they both start to move when the pressure in the chamber 102 is 
reduced at the start of the injection cycle. Contact between the piston 
122 and the nozzle needle valve 92 occurs after both have begun to move. 
If the closing pressure, after this contact, is higher than the 
accumulator pressure, that is, the pressure in the chambers 74 and 84, the 
nozzle needle valve 92 will be quickly moved back to its seated or closed 
position and after only a very small quantity of fuel has been injected 
through the orifices 78. 
The embodiment of the accumulator nozzle illustrated in FIG. 3 and 
described hereinbelow has a structure and function generally similar to 
that of the embodiment of the nozzle 24 shown in FIG. 2. Accordingly, only 
the structural differences will be specifically described herein, and the 
same reference numerals will be used in FIG. 3 for the components of the 
accumulator nozzle 24 that are common with those in the FIG. 2 embodiment. 
The principal difference between the FIG. 2 and FIG. 3 embodiments is that 
the moveable piston 122 is replaced in the latter by a cylindrical 
displacement piston 138. That piston is disposed in a fourth chamber 142 
formed in the body 68 of the accumulator nozzle 24. This chamber 142 is 
cylindrical and has a first end 144 and a second end 146. A restricted 
passage 148 provides a restricted fluid connection between the first end 
144 of the chamber 142 and the accumulator chamber 74 while a restricted 
passage 152 provides a restricted fluid connection between the end 146 of 
the chamber 142 and the third chamber 102. Although both passages 148 and 
152 are shown as being restricted, the FIG. 3 embodiment will function 
with only one of the passages being restricted. 
The displacement piston 138 is moveable in the fourth chamber 142 between 
its first and second ends 144 and 146. The dimensions and tolerances 
betWeen the radial outer surface of the piston 138 and the cylindrical 
side wall of the cylindrical chamber 142 are such that there is no fluid 
connection around the piston 138. 
A coil compression 154 is disposed within the fourth chamber 142 between 
the piston 138 and the end 146 of that chamber. This spring serves to bias 
the piston 138 to position adjacent to the end 144 of the chamber 142. 
As before, when the injection cycle of the accumulator nozzle 42 begins, 
that is, when the valve 62 is moved, under the control of the controller 
64, to a position whereby the injection line 38 and the third chamber 102 
are vented to the sump 57, the pressure differential between the 
accumulator chamber 74 and the third chamber 102 is such that the piston 
138 moves away from its "rest" position (that is, its position adjacent 
the end 144 of the chamber 142) toward the end 146 of the chamber. 
As before, the amount of fuel injected by the accumulator nozzle 24 is 
determined by the difference between the charging pressure and the closing 
pressure. The minimum quantity of fuel injected is obtained when the 
charging pressure is just enough to open the nozzle. The maximum injected 
quantity is obtained when the charging pressure is at its maximum value. 
In order to obtain a satisfactory turn down ratio in prior accumulator 
nozzles, it was heretofore necessary to employ excessively large charging 
pressure. Such higher charging pressures presented a serious problem and 
required extra expense, reduced the life of the hydraulic equipment, and 
wasted power. 
The inclusion of the displacement piston 138 overcomes this long standing 
problem. This relatively small displacement piston 138 drops the pressure 
of the fuel stored in the accumulator chamber 74, immediately after the 
nozzle needle valve 92 starts to open, by a preselected amount that may be 
nearly as large as the difference between the opening and closing pressure 
when the maximum charging pressure is at or close to the opening pressure. 
With this preselected pressure drop, the minimum fuel quantity injected 
into the engine cylinder 12 may be very small. Since the displacement 
piston 138, however, discards only the same small quantity of fuel at all 
times, it does not subtract all that much fuel from an injection when the 
maximum charging pressure exists in the chamber 74 at the time an 
injection cycle commences. Accordingly, the turn down ratio of the nozzle 
24 may be very large. 
It should also be particularly noted that the displacement piston 138 
(specifically, the portion of the chamber 142 between the piston 138 and 
the end 144) communicates with the accumulator chamber 74 through the 
restricted passage 148. Thus, when the pressure in the chamber 102 is 
reduced (at the time the nozzle 24 is "fired") and when the nozzle needle 
valve 92 begins to open, the displacement piston 138 moves as well. 
Although because of the restriction in the passage 148, the piston 138 
does not complete its motion until after the nozzle needle valve 92 is 
partway open as, for example, ten percent of its stroke. If the pressure 
in the accumulator chamber 74 has dropped, by that time, below the closing 
pressure, the needle valve 92 will reverse its direction and close the 
orifices 78 with only a small quantity of fuel having been injected. On 
the other hand, if the fuel pressure of charging pressure in the 
accumulator chamber 74 remains high, the injection will proceed normally 
except for the small quantity of fuel discarded by the opening movement of 
the displacement piston 138. 
Referring now to FIG. 4, this graph illustrates how the fuel pressure 
changes over time where fuel injection occurs under maximum charging 
pressures and where the charging pressure is very close to the opening 
pressure. The arrow, identified by the reference number 158, indicates the 
pressure differential between the maximum charging pressure and the 
closing pressure while the arrow identified by the reference number 162, 
indicates the pressure differential between the opening and closing 
pressures. As illustrated in this FIG. 4 graph, which as noted above shows 
what would occur in a prior art accumulator nozzle, a turn down ratio of 
the order of 5.3 would be achieved. 
FIG. 5 discloses a similar fuel pressure vs. time relationship as that 
shown in FIG. 4. This illustrated relationship would occur when the 
accumulator nozzle 24 includes the moveable piston. It demonstrates the 
effect of that piston on the closing pressure. The reference number 164 
indicates the closing pressure if there were no contact between the piston 
122 and the nozzle needle valve 92. The reference number 166 indicates the 
increased closing pressure that would exist after the piston 122 abuts the 
end 94 of the nozzle needle valve 92. In this embodiment of the nozzle 24, 
the turn down ratio (calculated in a similar manner to that used in 
calculating the turn down ratio in the FIG. 4 nozzle) would be of the 
order of 25.7. 
FIG. 6 shows a comparable fuel pressure vs. time relationship to that 
illustrated in FIGS. 4 and 5. The relationship, it is believed, would 
occur when the accumulator nozzle 24 includes a displacement piston 138. 
The reference number 168 indicates the amount of the pressure drop that 
occurs through the use of the displacement piston 138. Again, the turn 
down ratio, similarly calculated, would be of the order of 11.7. 
Thus, it is apparent from FIGS. 4-6 that substantial increases in the turn 
down ratio may be achieved by the inclusion of either a movable piston 
122, or alternatively, a displacement piston 138 in an accumulator nozzle 
24. These increases in the turn down ratio make practical and feasible the 
use of accumulator nozzles, with all their known benefits, in a diesel 
engine fuel injection system. The usage of such improved accumulator 
nozzles should enable such systems to substantially reduce pollution 
caused by incomplete combustion. 
The accumulator nozzle 24 and its subassembly 33 have been described in 
detail. As noted above, similar accumulator nozzles 26, 28 and 32 would be 
used with their associated engine cylinders 14, 16, 18, respectively. 
Moreover, the subassemblies 172, 174 and 176 of the nozzles 26, 28 and 32, 
respectively, are likewise identical in structure and function to the 
subassembly 33 (and its above described components). Also secondary valves 
178, 182 and 184 are utilized with the nozzles 26, 28 and 32, and their 
associated subassemblies 172, 174 and 176, respectively. These valves 178, 
182 and 184 are structurally and functionally identical to the valve 62, 
and like the valve 62, are controlled by the controller 64. 
The preferred embodiments of the present invention have now been described. 
These preferred embodiments constitute the best mode contemplated by the 
inventor for carrying out his invention. Because his invention may be 
copied, without copying the precise details of the preferred embodiments, 
the following claims particularly point out and distinctly claim the 
subject matter which the inventor regards as his invention and wishes to 
protect.