Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-08-02
2004-02-03
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S300000, C123S496000
Reexamination Certificate
active
06684853
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is related to the fuel supply for internal combustion engines and, more particularly, to a fuel injector having two active control valves to control needle valve motion. One control valve is used to control the injection pressure process. The second control valve is used to directly control the fuel injector needle valve. Depending on the coordination between two control valves, different injection characteristics are obtained as desired.
THE PRIOR ART
A hydraulically-actuated, electronically-controlled, unit injector (HEUI), of the type described in U.S. Pat. No. 5,181,494 and in SAE Technical Paper Series 930270,
HEUI—A New Direction for Diesel Engine Fuel Systems,
S. F Glassey, at al, March 1-5, 1993, which are incorporated herein by reference, is depicted in prior art FIG.
1
.
The prior art HEUI
200
is depicted in prior art FIG.
1
. HEUI
200
consists of four main components: (1) control valve
202
; (2) intensifier
204
; (3) nozzle
206
; and (4) injector housing
208
.
The purpose of the control valve
202
is to initiate and end the injection process. Control valve
202
is comprised of a poppet valve
210
, and electric control
212
having an armature and solenoid. High pressure actuating oil is supplied to the lower seat
214
of the valve
210
through oil passageway
216
. To begin injection, the solenoid of electric control
212
is energized, moving the poppet valve
210
upward off the lower seat
214
to the upper seat
218
. This action admits high pressure oil to the spring cavity
220
and the passage
222
to the intensifier
204
. Injection commences and continues until the solenoid of the control
212
is de-energized and the poppet
210
moves from the upper seat
218
to lower seat
214
. Oil and fuel pressure decrease as spent actuating oil is ejected from the injector
200
through the open upper seat oil discharge
224
to the valve cover area (not shown) of the internal combustion engine.
The middle segment of the injector
200
is comprised of the hydraulic intensifier piston
236
, the plunger
228
, the plunger chamber
230
, and the plunger return spring
232
.
Intensification of the fuel pressure to desired injection pressure levels is accomplished by the ratio of areas between the upper surface
234
of the intensifier piston
236
and the lower surface
238
of the plunger
228
. The intensification ratio can be tailored to achieve desired injection characteristics. Injection begins as high pressure actuating oil is supplied to the upper surface
234
of the intensifier piston
236
. Fuel is admitted to the plunger chamber
230
(formed in part by lower surface
238
) through passageway
240
past check valve
242
.
As the piston
236
and plunger
228
move downward, the pressure of the fuel in plunger chamber
230
below the lower surface
238
of the plunger
228
rises. High pressure fuel flows in passageway
244
past check valve
246
to act upward on needle valve
250
. The upward force opens needle valve
250
and fuel is discharged from orifice
252
. The piston
236
continues to move downward until the solenoid of the control
212
is de-energized, causing the poppet
210
to return to the lower seat
214
, thereby blocking actuating oil flow. Oil pressure above the intensifier piston is now vented to the ambient through drain passage
224
. The plunger return spring
232
returns, the piston
236
and plunger
228
to their initial positions. As the plunger
228
returns, the plunger
228
draws replenishing fuel into the plunger chamber
230
across ball check valve
242
.
The nozzle
206
is typical of other diesel fuel system nozzles. The valve-closed-orifice style is shown, although a mini-sac version of the tip is also available. Fuel is supplied to the nozzle orifice
252
through internal passages. As fuel pressure increases, the nozzle needle valve
250
is lifted from the lower seat
254
(compressing spring
256
), thereby opening the needle valve
250
and causing fuel injection to occur. As fuel pressure decreases at the end of injection, the spring
256
returns the needle valve
250
to its closed position on the lower seat
254
.
The HEUI Intensifier System
For all unit injectors in production today, there is only one active control valve in each injector. Fuel injectors are typically of the common rail or intensifier types. The common rail type (Lucas and Bosch type systems) has a very high pressure fuel rail that supplies fuel to the injector at a pressure ready for injection, on the order of 20,000 psi. The intensifier injector (HEUI type) includes an intensifier plunger in the injector itself to bring low supply fuel pressure to a desired injection pressure level internally. This process is as described above.
One of very desired characteristics of the HEUI intensifier system is its similarity in performance to the Bosch type pump and nozzle injection system (cam system), where injection pressure is gradually built up during an injection event. This gradual building up process produces a generally triangle shaped rate-of-injection single shot injection event where the initial portion of the injection pressure rate trace rises gradually, as distinct from a sharp rising. See
FIG. 3
, case
4
. This type of injection rate trace provides a benefit to reduce NOx emissions at high speed engine operation. This is a very special feature of the intensifier system. Common rail systems can not produce this feature.
In the HEUI injector concept shown in U.S. Pat. No. 5,460,329, pilot injection is produced through double action of a single spool digital control valve. The result is similar to the solid line injection event depicted in
FIG. 3
, case
1
. The entire injection event, having a pilot injection event preceding a main injection event, is considered as two independent, pulse-width-controlled, single injection events occurring in very close sequence. The pilot portion of injection is a single shot of injection but with very short pulse width. With this philosophy, the intensifier chamber pressure is vented to terminate the pilot injection at the end of the pilot injection event and recharged again to start the main injection.
The HEUI B injector, described in U.S. Pat. No. 5,682,858, improves its performance by using direct control of the needle valve. However, the intensifier is also passively controlled by the same control valve. The actuation process is not totally independent of needle timing control. This type of injector cannot have fully flexible injection timing and rate shaping control across the whole engine speed and load range. It may have difficulty producing certain dwell and certain pilot injection size when the actuation pressure is mismatched. Another desirable characteristic of the intensifier system is its product safety. High injection pressure is developed within the injector only during a short period during the engine cycle, only during the time window where injection events are going to occur, as distinct from a high pressure common rail system. The injector stays in a low pressure environment for the rest of the engine cycle. Additionally, there is no external plumbing required to transport fuel from a high pressure pump to the injector as in the common rail system. Compared to the common rail system, the intensifier system demonstrates a much superior advantage that appeals to a large number of engine manufacturers.
Common Rail Systems (Lucas & Bosch Type Systems)
The common rail fuel system is very different from the previously described injectors that incorporate an intensifier system. In the common rail system, the injector is not responsible for the injection pressure development process. Rather, the high pressure fuel, on the order of 20,000 psi is delivered to the injector from the common rail ready for injection into the combustion chamber of an engine. The injector has direct timing control of the injector needle valve with a relatively simple timing control process to produce the desired pilot injection and injection event dwell
Calfa Jeffrey P.
International Engine Intellectual Property Company LLC
Lukasik Susan L.
Miller Carl S.
Sullivan Dennis Kelly
LandOfFree
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