Method for controlling a hydraulically-actuated fuel injections system to start an engine

In one aspect of the present invention, a method is disclosed that controls the pressure of actuating fluid supplied to a hydraulically-actuated injector. A target engine speed acceleration is determined, and compared to the actual engine speed acceleration to determine a desired actuating fluid pressure in order to control the fuel injection rate to start the engine.

TECHNICAL FIELD 
The present invention relates generally to hydraulically-actuated fuel 
injection systems and, more particularly to electronic control systems for 
independently controlling the fuel injection rate and duration to start an 
engine. 
1. Background Art 
A diesel engine achieves combustion by injecting fuel that vaporizes into 
the hot air of an engine cylinder. However, during cold starting 
conditions, the air loses much of its heat to the cylinder walls making 
engine starting difficult. For example, if too much fuel is injected into 
the cylinder, the heat required to vaporize the cold fuel reduces the air 
temperature and may prevent or quench combustion. However, when the engine 
has fired and is accelerating to running speed, the fuel injection rate 
must be increased in order to inject the fuel within the proper crank 
angle orientation. It is then critical that fuel be injected at a rate 
which is not too slow that inhibits acceleration, nor too fast that 
quenches the combustion. 
The present invention is directed to overcoming one or more of the problems 
as set forth above. 
2. Disclosure of the Invention 
In one aspect of the present invention, a method is disclosed that controls 
the pressure of actuating fluid supplied to a hydraulically-actuated 
injector. A target engine speed acceleration is determined, and compared 
to the actual engine speed acceleration to determine a desired actuating 
fluid pressure in order to control the fuel injection rate to start the 
engine.

BEST MODE FOR CARRYING OUT THE INVENTION 
The present invention relates to an electronic control system for use in 
connection with a hydraulically actuated electronically controlled unit 
injector fuel system. Hydraulically actuated electronically controlled 
unit injector fuel systems are known in the art. One example of such a 
system is shown in U.S. Pat. No. 5,191,867, issued to Glassey on Mar. 9, 
1993, the disclosure of which is incorporated herein by reference. 
Throughout the specification and figures, like reference numerals refer to 
like components or parts. Referring first to FIG. 1, a preferred 
embodiment of the electronic control system 10 for a hydraulically 
actuated electronically controlled unit injector fuel system is shown, 
hereinafter referred to as the HEUI fuel system. The control system 
includes an Electronic Control Module 15, hereinafter referred to as the 
ECM. In the preferred embodiment the ECM is a Motorolla microcontroller, 
model no. 68HC11. However, many suitable controllers may be used in 
connection with the present invention as would be known to one skilled in 
the art. 
The electronic control system 10 includes hydraulically actuated 
electronically controlled unit injectors 25a-f which are individually 
connected to outputs of the ECM by electrical connectors 30a-f 
respectively. In FIG. 1, six such unit injectors 25a-f are shown 
illustrating the use of the electronic control system 10 with a six 
cylinder engine 55. However, the present invention is not limited to use 
in connection with a six cylinder engine. To the contrary, it may be 
easily modified for use with an engine having any number of cylinders and 
unit injectors 25. Each of the unit injectors 25a-f is associated with an 
engine cylinder as is known in the art. Thus, to modify the preferred 
embodiment for operation with an eight cylinder engine would require two 
additional unit injectors 25 for a total of eight such injectors 25. 
Actuating fluid is required to provide sufficient pressure to cause the 
unit injectors 25 to open and inject fuel into an engine cylinder. In a 
preferred embodiment the actuating fluid comprises engine oil and the oil 
supply is the engine oil pan 35. Low pressure oil is pumped from the oil 
pan by a low pressure pump 40 through a filter 45, which filters 
impurities from the engine oil. The filter 45 is connected to a high 
pressure fixed displacement supply pump 50 which is mechanically linked 
to, and driven by, the engine 55. High pressure actuating fluid (in the 
preferred embodiment, engine oil) enters an Injector Actuation Pressure 
Control Valve 76, hereinafter referred to as the IAPCV. Other devices, 
which are well known in the art, may be readily and easily substituted for 
the fixed displacement pump 50 and the IAPCV. For example, one such device 
includes a variable pressure high displacement pump. 
In a preferred embodiment, the IAPCV and the fixed displacement pump 50 
permits the ECM to maintain a desired pressure of actuating fluid. A check 
valve 85 is also provided. 
The ECM contains software decision logic and information defining optimum 
fuel system operational parameters and controls key components. Multiple 
sensor signals, indicative of various engine parameters are delivered to 
the ECM to identify the engine's current operating condition. The ECM uses 
these input signals to control the operation of the fuel system in terms 
of fuel injection quantity, injection timing, and actuating fluid 
pressure. For example, the ECM produces the waveforms required to drive 
the IAPCV and a solenoid of each injector 25. 
The electronic control uses several sensors, some of which are shown. An 
engine speed sensor 90 reads the signature of a timing wheel applied to 
the engine camshaft to indicate the engine's rotational position and speed 
to the ECM. An actuating fluid pressure sensor 95 delivers a signal to the 
ECM to indicate the actuating fluid pressure. Moreover, an engine coolant 
temperature sensor 97 delivers a signal to the ECM to indicate engine 
temperature. 
The injector operation will now be described with reference to FIG. 2. The 
injector 25 consists of three main components, a control valve 205, an 
intensifier 210, and a nozzle 215. The control valve's purpose is to 
initiate and end, the injection process. The control valve 205 includes a 
poppet valve 220, armature 225 and solenoid 230. High pressure actuating 
fluid is supplied to the popper valve's lower seat via passage 217. To 
begin injection, the solenoid is energized moving the poppet valve from 
the lower seat to an upper seat. This action admits high pressure fluid to 
a spring cavity 250 and to the intensifier 210 via passage 255. Injection 
continues until the solenoid is de-energized and the poppet moves from the 
upper to the lower seat. Fluid and fuel pressure decrease as spent fluid 
is ejected from the injector through the open upper seat to the valve 
cover area. 
The intensifier 210 includes a hydraulic intensifier piston 235, plunger 
240, and return spring 245. Intensification of the fuel pressure to 
desired injection pressure levels is accomplished by the ratio of areas 
between the intensifier piston 235 and plunger 240. Injection begins as 
high pressure actuating fluid is supplied to the top of the intensifier 
piston. As the piston and plunger move downward, the pressure of the fuel 
below the plunger rises. The piston continues to move downward until the 
solenoid is de-energized causing the popper 220 to return to the lower 
seat, blocking fluid flow. The plunger return spring 245 returns the 
piston and the plunger to their initial positions. As the plunger returns, 
it draws replenishing fuel into the plunger chamber across a ball check 
valve. 
Fuel is supplied to the nozzle 215 through internal passages. As fuel 
pressure increases, a needle lifts from a lower seat allowing injection to 
occur. As pressure decreases at the end of injection, a spring 265 returns 
the needle to its lower seat. 
Because of the physical characteristics of the fuel injector and the 
actuating fluid flow dynamics, at high actuating fluid viscosities and low 
actuating fluid pressures, multiple fuel injections may occur during the 
injection period. 
More particularly, as the injector 25 dispenses fuel, the intensifier 
plunger 240 moves downward, which causes actuating fluid to flow into the 
control valve cavity 250. However, at high actuating fluid viscosities, 
actuating fluid flow losses develop, which decreases the actuating fluid 
pressure in the control valve cavity 250. If the pressure in the control 
valve cavity 250 drops below a predetermined value, the corresponding drop 
in fuel injection pressure will cause the needle 260 to close. However, as 
pressure builds in the control valve cavity, the fuel injection pressure 
will increase, causing the needle to open and once again dispense fuel. 
This repeated opening and closing of the needle may continue during the 
entire injection period causing fuel to be injected in a series of very 
short bursts. Consequently, multiple injection may provide many beneficial 
effects including lower emissions, reduced noise, reduced smoke, improved 
cold starting, white smoke clean-up, and high altitude operation. 
Typically, engine starting includes three engine speed ranges. For example, 
from 0-200 RPM the engine is said to be cranking (cranking speed range). 
Once the engine fires, then the engine speed accelerates from engine 
cranking speeds to engine running speeds (acceleration speed range). Once 
the engine speed reaches a predetermined engine RPM, e.g. 900 RPM, then 
the engine is said to be running (running speed range). The present 
invention is concerned with controlling the fuel injection to start an 
engine where the engine is accelerating to running speed--especially where 
the engine temperature is below a predetermined temperature, e.g. 
18.degree. Celsius. 
The software decision logic for determining the magnitude of the actuating 
fluid pressure supplied to the injector 25, while the engine is firing, 
but not yet running, is shown with respect to FIG. 3. A target 
acceleration rate signal ds.sub.t is produced by block 305, which may 
includes a map(s) and/or equation(s). Preferably, the target acceleration 
rate signal ds.sub.t is a function of coolant temperature T.sub.c. The 
target engine speed derivative signal ds.sub.t is then compared with the 
actual engine acceleration rate signal ds.sub.f at block 310, which 
produces an engine acceleration rate error signal ds.sub.e. The actual 
engine acceleration rate signal ds.sub.f is produced by differentiating an 
actual engine speed signal s.sub.f, at block 315. Preferably, the raw 
engine speed signal s.sub.r is conditioned and converted by a conventional 
means 317 to eliminate noise and convert the signal to a usable form. 
The engine acceleration rate error signal ds.sub.e is converted into a 
desired actuating fluid pressure signal P.sub.d, at block 320, in response 
to integrating the engine acceleration rate error signal ds.sub.e. Note, 
the magnitude of the desired actuating fluid pressure signal P.sub.d may 
be limited to an upper magnitude commensurate with the pressure limits of 
the HEUI system, while the lower magnitude may be limited to the pressure 
at which the engine initially fired. The desired actuating fluid pressure 
signal P.sub.d is then compared, at block 325, with the actual actuating 
fluid pressure signal P.sub.f to produce an actuating fluid pressure error 
signal P.sub.e. 
The actuating fluid pressure error signal P.sub.e is input to a PI control 
block 330 whose output is a desired electrical current (I) applied to the 
IAPCV. By changing the electrical current (I) to the IAPCV the actuating 
fluid pressure P.sub.f can be increased or decreased. The PI control 330 
calculates the electrical current (I) to the IAPCV that would be needed to 
raise or lower the actuating fluid pressure P.sub.f to result in a zero 
actuating fluid pressure error signal P.sub.e. The resulting actuating 
fluid pressure is used to hydraulically actuate the injector 25. 
Preferably, the raw actuating fluid pressure signal P.sub.r in the high 
pressure portion of the actuating fluid pressure circuit 335 is 
conditioned and converted by a conventional means 340 to eliminate noise 
and convert the signal to a usable form. Although a PI control is 
discussed, it will be apparent to those skilled in the art that other 
controlled strategies may be utilized. 
The software decision logic for determining the time duration over which 
fuel is injected by each injector 25 while the engine is firing, but not 
yet running, is shown with respect to FIG. 4. Preferably, the actual 
engine coolant temperature signal T.sub.c is input into block 405, may 
include a map(s) and/or equation(s). Based on the magnitude of the coolant 
temperature, a cranking duration limit signal D is selected as an output. 
The cranking duration limit signal D represents the period, in angular 
degrees, over which fuel is to be injected. The cranking duration limit 
signal D, along with an actual engine speed signal is input into block 
410, which converts the cranking duration limit signal D into a time 
duration signal t.sub.d expressed in temporal units, e.g., milliseconds. 
The time duration signal t.sub.d is used to determine how long the current 
(I) to the solenoid of a respective injector 25 should remain "on" to 
inject the correct quantity of fuel. 
Thus, while the present invention has been particularly shown and described 
with reference to the preferred embodiment above, it will be understood by 
those skilled in the art that various additional embodiments may be 
contemplated without departing from the spirit and scope of the present 
invention. 
Industrial Applicability 
The subject invention electronically controls the fuel injection rate and 
fuel injection duration to start an engine. More particularly, the present 
invention is adapted to increase the injection rate while the engine is 
accelerating to running speeds in order to achieve quicker starting. 
Because the time period in which to inject fuel decreases, as engine speed 
increases, the injection rate must be increased accordingly. Consequently, 
the present invention increases the fuel injection rate by increasing the 
actuating fluid pressure to a achieve a desired quantity of fuel to 
accelerate the engine at a desired acceleration rate. 
The present invention determines the engine speed acceleration, and 
compares the engine speed acceleration to a target acceleration value to 
determine a desired actuating fluid pressure to control the fuel injection 
rate. Advantageously, the target engine speed acceleration is a function 
of temperature to account for the combustion characteristics of the 
engine. Consequently, the desired actuating fluid pressure results in an 
injection rate that is neither too slow which inhibits engine 
acceleration, nor too fast which quenches combustion. 
Moreover, in a HEUI fuel system, the injection rate is responsive to the 
actuating fluid pressure and viscosity. Accordingly, the acceleration rate 
is responsive to viscosity. For example, the higher the viscosity, the 
greater amount of pressure is required to result in the desired 
acceleration rate; conversely, the lower the viscosity, the lessor amount 
of pressure is required to result in the desired acceleration rate. 
Other aspects, objects and advantages of the present invention can be 
obtained from a study of the drawings, the disclosure and the appended 
claims.