Method for delivering a small quantity of fuel with a hydraulically-actuated injector during split injection

A method for apportioning a total fuel quantity to be injected to an engine by a hydraulically-actuated injector between a pilot shot and a main shot includes determining a pilot shot and/or main shot fuel quantity desired to be delivered during injection. The desired pilot shot fuel quantity is compared with a threshold pilot shot fuel quantity and/or the desired main shot fuel quantity is compared with a threshold main shot fuel quantity. The total fuel quantity is delivered by a pilot shot if the desired pilot shot fuel quantity is less than the threshold pilot shot fuel quantity and/or the desired main shot fuel quantity is less than the threshold main shot fuel quantity.

TECHNICAL FIELD 
This invention relates generally to hydraulically-actuated fuel injection 
systems, and more particularly, to an electronic control system and method 
for controlling fuel injection during split injection engine operating 
conditions so as to enable accurate delivery of a small quantity of fuel 
to the engine. 
BACKGROUND ART 
During certain engine operating conditions it is desirable to inject fuel 
using a split injection technique in which a portion of the total fuel to 
be delivered to the engine cylinder is injected by what is commonly termed 
a pilot shot or prime shot and in which the remaining portion of the fuel 
is injected by what is commonly termed a main shot. For example, it is 
known to utilize such a split injection technique at engine operating 
conditions including low engine speed and low engine load. In the past the 
controllability of such split injection has been somewhat restricted by 
mechanical limitations of the hydraulically-actuated injectors utilized. 
For example, some injectors have been limited in that the pilot or prime 
shot was mechanically controlled and therefore both a pilot shot and a 
main shot always occurred. Even with a more advanced 
hydraulically-actuated electronically-controlled injector, during certain 
engine operating conditions the quantity of fuel desired to be delivered 
to the engine can be relatively small. It is sometimes difficult to 
accurately control delivery of such small amounts of fuel, even utilizing 
current control signals. 
Accordingly, the present invention is directed to overcoming one or more of 
the problems as set forth above. 
DISCLOSURE OF THE INVENTION 
In one aspect of the present invention a method for apportioning a total 
fuel quantity to be injected to an engine by a hydraulically-actuated 
injector between a pilot shot and a main shot is provided. The method 
includes determining a pilot shot and/or main shot fuel quantity desired 
to be delivered during injection. The desired pilot shot fuel quantity is 
compared with a threshold pilot shot fuel quantity and/or the desired main 
shot fuel quantity is compared with a threshold main shot fuel quantity. 
The total fuel quantity is delivered by a pilot shot if the desired pilot 
shot fuel quantity is less than the threshold pilot shot fuel quantity 
and/or the desired main shot fuel quantity is less than the threshold main 
shot fuel quantity. A fuel injection control system which operates in 
accordance with the inventive method is also provided. 
The pilot shot may be a ramped fuel delivery which allows for more accurate 
control of delivery of small amounts of fuel to the engine, the premise 
behind the invention being that delivery of the total fuel quantity by a 
pilot shot will provide more accurate and repeatable fuel delivery as the 
total fuel quantity to be delivered approaches zero.

BEST MODE FOR CARRYING OUT OF INVENTION 
Referring to FIG. 1, there is shown a hydraulically-actuated 
electronically-controlled fuel injector system 10 (hereinafter referred to 
as HEUI-B fuel system). Typical of such systems are those shown and 
described in U.S. Pat. No. 5,463,996, U.S. Pat. No. 5,669,355, U.S. Pat. 
No. 5,673,669, U.S. Pat. No. 5,687,693, and U.S. Pat. No. 5,697,342. The 
exemplary HEUI-B fuel system is shown in FIG. 1 as adapted for a 
direct-injection diesel-cycle internal combustion engine 12. 
HEUI-B fuel system 10 includes one or more hydraulically-actuated 
electronically-controlled injectors 14, such as unit fuel injectors, each 
adapted to be positioned in a respective cylinder head bore of engine 12. 
The system 10 further includes apparatus or means 16 for supplying 
hydraulic actuating fluid to each injector 14, apparatus or means 18 for 
supplying fuel to each injector, apparatus or means 20 for electronically 
controlling the manner in which fuel is injected by injectors 14, 
including timing, number of injections, and injection profile, and 
actuating fluid pressure of the HEUI-B fuel system 10 independent of 
engine speed and load. Apparatus or means 22 for recirculating or 
recovering hydraulic energy of the hydraulic actuating fluid supplied to 
injectors 14 is also provided. 
Hydraulic actuating fluid supply means 16 preferably includes an actuating 
fluid sump 24, a relatively low pressure actuating fluid transfer pump 26, 
an actuating fluid cooler 28, one or more actuating fluid filters 30, a 
source or means 32 for generating relatively high pressure actuating 
fluid, such as a relatively high pressure actuating fluid pump 34, and at 
least one relatively high pressure fluid manifold 36. The actuating fluid 
is preferably engine lubricating oil. Alternatively the actuating fluid 
could be fuel. 
Apparatus 22 may include a waste actuating fluid control valve 35 for each 
injector, a common recirculation line 37, and a hydraulic motor 39 
connected between the actuating fluid pump 34 and recirculation line 37. 
Actuating fluid manifold 36, associated with injectors 14, includes a 
common rail passage 38 and a plurality of rail branch passages 40 
extending from common rail 38 and arranged in fluid communication between 
common rail 38 and actuating fluid inlets of respective injectors 14. 
Common rail passage 38 is also arranged in fluid communication with the 
outlet from high pressure actuating fluid pump 34. 
Fuel supplying means 18 includes a fuel tank 42, a fuel supply passage 44 
arranged in fluid communication between fuel tank 42 and a fuel inlet of 
each injector 14, a relatively low pressure fuel transfer pump 46, one or 
more fuel filters 48, a fuel supply regulating valve 49, and a fuel 
circulation and return passage 50 arranged in fluid communication between 
injectors 14 and fuel tank 42. The various fuel passages may be provided 
in a manner commonly know in the art. 
Electronic controlling means 20 preferably includes an electronic control 
module (ECM) 56, the use of which is well known in the art. ECM 56 
typically includes processing means such as a microcontroller or 
microprocessor, a governor (GOV) such as a proportional integral 
derivative (PID) controller for regulating engine speed, and circuitry 
including input/output circuitry and the like. ECM 56 may be used to 
control fuel injection timing, fuel quantity injected, fuel injection 
pressure, number of separate injections per injection cycle, time 
intervals between injection segments, and fuel quantity injected by each 
injection segment. Each of such parameters are variably controllable 
independent of engine speed and load. 
Associated with a camshaft of engine 12 is an engine speed sensor 58 which 
produces speed indicative signals. Engine speed sensor 58 is connected to 
the governor of ECM 56 for monitoring of the engine speed and piston 
position for timing purposes. A throttle 60 is also provided and produces 
signals indicative of a desired engine speed, throttle 60 also being 
connected to the governor of ECM 56. An actuating fluid pressure sensor 62 
for sensing the pressure within common rail 38 and producing pressure 
indicative signals is also connected to ECM 56 which utilizes such signals 
for maintaining or adjusting the actuating fluid pressure. 
Each of the injectors 14 is preferably of a type such as that shown and 
described in one of U.S. Pat. No. 5,463,996, U.S. Pat. No. 5,669,355, U.S. 
Pat. No. 5,673,669, U.S. Pat. No. 5,687,693, and U.S. Pat. No. 5,697,342. 
However, it is recognized that the present invention could be utilized in 
association with other variations of hydraulically-actuated 
electronically-controlled injectors. 
Given HEUI-B fuel system 10, it is recognized that the type of injection 
desired will typically vary depending upon various engine operating 
conditions. Referring to FIG. 2, a graph of engine speed verses engine 
load is shown, illustrating that at relatively low engine speeds and 
relatively low engine loads, as indicated by region 64, it is often 
desirable to utilize what is commonly referred to as a split injection 
technique, wherein a portion of the total fuel to be delivered to the 
engine cylinder is injected by what is commonly termed a pilot shot or 
prime shot and in which the remaining portion of the fuel is injected by 
what is commonly termed a main shot. Such split injection can provide 
advantages in terms of exhaust emissions, including reduced particulate 
emissions and/or reduced NO.sub.X emissions. 
An exemplary current waveform for such split injection is illustrated in 
FIG. 3 showing a prime shot control signal 66 and a main shot control 
signal 68, with a delay 70 therebetween. The duration of each of control 
signals 66 and 68 can be varied by ECM 56, and the duration of delay 70 
can also be varied by ECM 56. Referring to FIG. 4, a graph of the fuel 
injection rate verses time for the split injection control signals of FIG. 
3 is shown. The injection rate resulting from the pilot shot increases in 
a ramped manner as shown at 72 because the fuel within the injector is 
being pressurized during the pilot shot control signal by movement of a 
plunger within the injector. The injection rate resulting from the main 
shot is higher and relatively constant as shown at 74 because, even after 
the pilot shot control signal ceases, plunger movement within the injector 
continues due to inertia and the fuel is further compressed while a check 
valve at the injector nozzle remains closed so that no fuel is introduced 
into the cylinder. The quantity of fuel delivered during each of pilot 
shot control signal 66 and main shot control signal 68 is represented by 
the area of respective regions 72 and 74. In order to accurately deliver 
specific fuel quantities, opening and closing of the injectors must be 
accurately controlled by control signals 66 and 68. As shown in FIG. 4 
there will be some time lag between when control signals 66 and 68 are 
turned on and off and when injection begins and stops. Therefore, there 
will occasionally be some difficulty encountered in accurately delivering 
fuel quantities as the total fuel quantity to be injected approaches zero, 
such as at very low engine speeds and very low engine loads. It can be 
seen from FIG. 4 that the pilot shot can be utilized to accurately deliver 
smaller quantities of fuel than can the main shot because the injection 
rate is generally lower. It is this aspect of split injection which is 
advantageously utilized in the present invention. 
Operating steps in accordance with one embodiment of the present invention 
are set forth in flowchart 100 of FIG. 5. The rail pressure, total fuel 
quantity, and actual engine speed are determined as indicated at step 102. 
The rail pressure determination is based upon one or more signals from 
actuating fluid pressure sensor 62; the total fuel quantity is the fuel 
rate output by the governor; and the actual engine speed determination is 
based upon one or more signals from engine speed sensor 58. A pilot shot 
fuel quantity desired to be delivered during the injection cycle is 
determined at step 104 and the main shot fuel quantity desired to be 
delivered during the injection cycle is determined at step 106. The 
desired pilot shot fuel quantity may be calculated, or looked up in a map, 
as a function of engine speed and engine load, where the engine load 
indicator utilized may be the rail pressure, the total fuel quantity, or 
some other engine load indicator. The desired main shot fuel quantity may 
then be determined as the difference between the total fuel quantity and 
the desired pilot shot fuel quantity. 
A comparison of the desired main shot fuel quantity to a threshold main 
shot fuel quantity and/or of the desired pilot shot fuel quantity to a 
threshold pilot shot fuel quantity is then made at step 108. In this 
regard it is anticipated that the threshold main shot fuel quantity should 
be representative of a minimum fuel quantity which can accurately be 
delivered by a main shot control signal and the threshold pilot shot fuel 
quantity should be representative of a minimum fuel quantity which can 
accurately be delivered by a pilot shot control signal. Such fuel 
quantities will typically vary with the rail pressure and with the fuel 
delivery characteristics of the particular injector being utilized. 
Accordingly, the threshold main shot and threshold pilot shot fuel 
quantities may be calculated, or looked up in respective maps, as a 
function of rail pressure. Such maps could be determined based upon bench 
testing of the injector. If the desired main shot fuel quantity is less 
than the threshold main shot fuel quantity and/or the desired pilot shot 
fuel quantity is less than the threshold pilot shot fuel quantity, then 
the pilot shot fuel quantity to be delivered for such injection cycle is 
set to the total fuel quantity and the main shot fuel quantity for such 
injection cycle is set to zero at step 110. The pilot shot duration is 
determined and the main shot duration is set to zero at step 112. The 
pilot shot duration may be calculated, or looked up in a map, as a 
function of the rail pressure and the total fuel quantity. Fuel injection 
then takes place at step 114 with the total fuel quantity being delivered 
by a pilot shot utilizing a pilot shot control signal of appropriate 
duration. 
If neither the desired main shot fuel quantity nor the desired pilot shot 
fuel quantity are less than the threshold main shot and threshold pilot 
shot fuel quantities respectively, injection takes place as is normal for 
split injection. In particular, the pilot shot duration being determined 
at step 116, the main shot duration being determined at step 118, the 
delay between the pilot shot and main shot being determined at step 120, 
and fuel injection being affected by appropriate control signals at stop 
114. It is anticipated that the pilot shot duration and main shot duration 
will be calculated, or looked up in respective maps, as a function of rail 
pressure and respective fuel quantities. 
Industrial Applicability 
Utilization of an injection method or system in accordance with the present 
invention provides for more accurate delivery of small fuel quantities 
during split injection engine operating conditions. In particular, if a 
determination is made during split injection that either the desired main 
shot fuel quantity and/or the desired pilot shot fuel quantity cannot be 
accurately delivered, the total fuel quantity is delivered by a pilot 
shot. Although the pilot shot is a ramped injection, the timing associated 
with a split injection is maintained. Delivering the total fuel quantity 
by a pilot shot enables more accurate injection of small quantities of 
fuel due to the lower initial injection rate provided by the pilot shot as 
explained above with respect to FIG. 4. Such accuracy enables a more 
continuous and repeatable delivery of the total fuel quantity, thus 
preventing a rough idle situation. 
It is anticipated that rather than directly comparing the desired pilot 
shot fuel quantity and/or desired main shot fuel quantities with minimum 
or threshold fuel quantities in step 108, the pilot shot duration and main 
shot duration could first be determined. Such durations, being values 
which are indicative of fuel quantities desired to be delivered, could be 
compared with respective threshold duration values which are also 
indicative of fuel quantities. 
Although fuel system 10 has been shown as a six injector system, it is 
recognized that the present invention could be incorporated in fuel 
injection systems including any number of fuel injectors including, for 
example, two, four and eight injector systems. It is also recognized that 
flowchart 100 is merely representative of one manner of organizing the 
steps of the present invention and that other variations could be utilized 
without departing from the spirit of the present invention. 
Other aspects, objects and advantages of the present invention can be 
obtained from a study of the drawings, the disclosure and the appended 
claims.