Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2000-09-15
2002-02-26
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S494000, C123S447000
Reexamination Certificate
active
06349702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a common-rail fuel-injection system in which a series of injectors admits the fuel charge to each combustion chamber from a common rail filled with fuel maintained at a high pressure.
2. Description of the Prior Art
Common-rail fuel-injection systems have been conventionally known as the most suitable way to increase injection pressures and also control fuel-injection factors such as injection timing, amount of fuel injected per cycle and the like, depending on engine operating conditions. Among the prior common-rail fuel-injection systems there is a fuel-injection system in which working fluid for fuel injection pumped up to a preselected pressure is accumulated in a common rail to actuate injectors, which are arranged in individual cylinders, each to each cylinder. Fuel is charged out of the injectors into their associated combustion chambers by making use of the hydraulic pressure in the working fluid. A control unit governs valves installed in the individual injectors to inject the fuel with the fuel-injection factors optimal to the engine operating conditions.
In contrast, the common-rail fuel-injection system of fuel-pressure actuated type has been known in which fuel serves as the working fluid. In this type of fuel injection, the fuel pressures corresponding to the injection pressures are continually maintained in fuel passages from the common rail through injection lines to injection orifices formed at the distal ends of the injectors. Each injector is provided with a control valve allowing to flow or blocking the fuel supplied through the injection lines, and a solenoid-operated actuator to drive the control valve. A control unit regulates the fuel pressures in the common rail and the operation of the solenoid-operated actuators to inject the pressurized fuel out of the individual injectors in accordance with the injection factors most suitable for the engine operating conditions. Moreover, a further another type of the common-rail fuel-injection system has been proposed, in which the working fluid is provided by engine oil stored at a high pressure in the common rail. The engine oil applied to pressure chambers in the injectors from the common rail provides hydraulic pressures to boost the fuel in pressure to a desired pressure, which is supplied into intensifying chambers in the injectors.
Referring to
FIG. 7
, the prior common-rail fuel-injection system of fuel-pressure actuated type will be explained in detail hereinafter. Fuel drawn in by a fuel-feed pump
6
from a fuel tank
7
is applied to a high-pressure fuel-supply pump
1
, which is a variable-delivery high-pressure plunger pump driven from an engine to force the fuel into a common rail
2
. The fuel stored at high pressure in the common rail
2
is allowed to pass through injection lines
23
included in a fuel passage system to injectors
3
, which are installed in the cylinders, each to each cylinder, in accordance with the type of engine. The fuel finally is injected out of the individual injectors into their associated combustion chambers. The high-pressure fuel-supply plunger pump
1
, besides the type illustrated, may be any one of rotary-plunger pump and inline-plunger pump in accordance with the type of engine.
The high-pressure fuel-supply plunger pump
1
has a cam
10
driven by the engine output to operate the pump, and a plunger
11
riding on the cam
10
to move in and out, with the plunger
11
forming at its top surface a part of the inside barrel wall defining a pumping chamber
12
. An inlet valve
15
is arranged between the pumping chamber
12
and a fuel inlet line
13
, and acts to regulate an amount of fuel forced into the pumping chamber
12
from the fuel-feed pump
6
through the fuel inlet line
13
. A non-return valve
17
is disposed along a fuel discharge line
14
connecting the pumping chamber
12
with the common rail
2
, and may open when the pressure created by the high-pressure fuel-supply plunger pump
1
is become over a preselected delivery pressure.
In order to keep the common-rail pressure from unexpected rise due to, for example, abnormality in control system, there is a relief valve
20
, normally closed, which may open when subjected to a higher pressure than a preselected pressure, permitting the fuel held in the common rail
2
to escape to the fuel tank
7
through a relief line
21
with the result of reducing the common-rail pressure. Moreover, a pressure detector
22
monitors the common-rail pressure Pr, which is in turn signaled to a control unit
8
of electronic controlled module, which is commonly contracted to EMC.
The injectors
3
are hermetically fitted with sealing members in holes bored in a base member such as a cylinder head. The injectors
3
each comprise a needle valve
31
movable up and down in a injector body, injection orifices
32
formed at an distal end of an injection nozzle to open when the needle valve
31
lifts off its seat, thereby allowing the fuel injection into a combustion chamber, not shown. The needle valve
31
has a top surface
33
that provides a part of a balance chamber
30
, which is applied with the high-pressure fuel from the associated injection line
23
. A fuel passage
34
connected with the injection line
23
is opened to a fuel sac
35
formed around the needle valve
31
. The needle valve
31
exposed to the fuel sac
35
is subject to the fuel pressure at its first tapered surface
36
, thus encountering the hydraulic force to lift the needle valve
31
. On the other hand, the needle valve
31
encounters both of the downward thrust due to the fuel pressure in the balance chamber
30
and the return force of a return spring
47
.
While the high-pressure fuel in the common rail
2
is supplied to the balance chamber
30
through a fuel supply line
38
branching off from the injection line
23
, the fuel in the balance chamber
30
is expelled through a drain line
40
. The fuel supply line
38
and drain line
40
are provided respectively with throats
39
,
41
, that are defined such that the throat
41
is larger in effective cross-section area than another throat
39
. Moreover, the drain line
40
is provided therein with a valve
44
, which is to relieve the fuel in the drain line
40
to a fuel return line
46
.
Lift of the needle valve
31
depends on a kinetic balance among the upward and downward hydraulic forces and the return force. Control current from the control unit
8
energizes a solenoid
45
to open the valve
44
in the drain line
40
. Thus, since the fuel flow at the throat
39
is more restricted than at the throat
41
, the fuel pressure in the balance chamber
30
drops so that the force to lift the needle valve
31
off the seat overcomes the sum of the depressing force resulting from the fuel pressure in the balance chamber
30
and the resilient force of the return spring
47
to allow the needle valve
31
lifting off the seat with the fuel being injected out of the injection orifices
32
into the combustion chamber, not shown. As the valve
44
is made closed, the fuel pressure restored in the balance chamber
30
brings a second tapered surface
37
nearby the distal end of the needle valve
31
into engagement with a tapered valve seat to block the fuel passage between the injection orifices
32
and the fuel sac
35
. Thus, the fuel injection ceases. The unconsumed fuel remaining the injector may be expelled out of the balance chamber
30
through the drain line
40
and recovered into the fuel tank
7
through the fuel return line
46
.
The control unit
8
is applied with various signals of sensors
9
such as a crankshaft position sensor for detecting the engine rpm Ne, an accelerator pedal sensor for detecting the depression Ac of an accelerator pedal, and so on. The sensors
9
signaling the control unit
8
may also include other sensors for monitoring the engine operating conditions, for example, an engine coolant temperature sensor, an engine cylinder identifying sensor,
Browdy and Neimark
Isuzu Motors Limited
Miller Carl S.
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