Internal-combustion engines – Charge forming device – With fuel pump
Reissue Patent
2000-01-24
2002-04-09
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
With fuel pump
C123S467000, C123S179170
Reissue Patent
active
RE037633
ABSTRACT:
TECHNICAL FIELD
This invention relates to an accumulator fuel injection apparatus applied to internal combustion engines, such as a diesel engine.
BACKGROUND ART
The conventional fuel injection apparatuses for multi-cylinder engines include an apparatus of a fuel injection system (electronically controlled fuel injection system) in which the controlling of an injection rate and injection time is done by an electronic circuit, an apparatus of a common injection system (common-rail injection system) in which a fuel is distributed from an injection pump to combustion chambers through a common passage, and an apparatus of a pressure storage type injection system (accumulator injection system) in which a fuel is distributed from an injection pump to combustion chambers through a common passage and an accumulator. Since the fuel injection apparatuses themselves of these systems are not provided with an accumulator in which the fuel from an injection pump is temporarily stored, the supplying of the fuel to these apparatuses is done through a common rail, a common passage, i.e. an accumulator.
FIG. 8
shows an injector (which will hereinafter be referred to as a first conventional example) for a conventional accumulating fuel injection apparatus. Such a conventional injector is a pressure balancing type injector disclosed in, for example. Japanese Patent Laid-Open Nos. 165858/1994 and 282164/1987, which is formed so that a fuel is supplied to or discharged from a balancing chamber by turning on or off a solenoid valve, whereby a needle valve is seated on or lifted from a seat of the nozzle, and which is adapted to lift the needle valve from the seat by removing a needle valve closing fuel pressure applied to the interior of the balancing chamber, whereby the injection of the fuel is carried out. Such a structure will now be further described. A casing
31
of an injector
30
is provided therein with a guide bore
32
, a fuel storage chamber
33
and a control volume, i.e. a balancing chamber
32
. A needle valve
35
is provided slidably in the guide bore
31
The needle valve
35
comprises a larger-diameter portion
36
, and a smaller-diameter portion
37
integral with the larger-diameter portion
36
, and a needle
38
is provided on a lower end of the smaller-diameter portion
37
. The casing
31
is provided with a hole type injection nozzle
39
(refer to FIG.
11
), and the injection nozzle
39
has injection holes
40
at a lower end portion thereof. The injection nozzle
39
is also provided with a seat
41
on an inner surface of its lower end portion, and, when the needle
38
of the needle valve
35
sits on the seat
41
, the injection holes
40
are closed. In the hole type injection nozzle
39
, the fuel collected in a passage, which extends from the seat
41
to a combustion chamber, after the valve is closed is ejected (after-dripping) in some cases due to the high temperature and pressure variation in the combustion chamber, and the fuel becomes an unburnt gas to cause the HC in an exhaust gas to increase. Therefore, it is necessary that the volume (sack volume
49
) of a space extending from the seat
41
to the injection ports
40
be set as small as possible.
The casing
31
has a supply port
42
for introducing a high-pressure fuel from an accumulating pipe (not shown) into the interior thereof, and a flow passage communicating with this supply port
42
branches into two flow passages
43
,
44
, one flow passage
43
communicating with the balancing chamber
34
via an orifice B, the other flow passage
44
communicating with the fuel storage chamber
33
. The casing
31
further has an orifice A allowing communication of the balancing chamber
34
with the outside.
The casing
31
is provided with a solenoid valve
45
for opening and closing the orifice A. The high-pressure fuel introduced from the supply port
42
enters the balancing chamber
34
and fuel storage chamber
33
and works on the needle valve
35
. When the solenoid valve
45
is in an OFF-state, the orifice A (discharge passage
46
) is closed therewith. In the meantime, the high-pressure fuel is supplied to the balancing chamber
34
and fuel storage chamber
33
, so that the needle valve
35
is pressed against an inner lower surface of the injection nozzle due to a difference in the areas on which a pressure is exerted of the needle valve
35
with the injection ports
40
thereby put in a closed state. When a solenoid
47
of the solenoid valve
45
is excited, a valve disc
48
is attracted thereto, and the orifice A is opened, so that the pressure in the balancing chamber
34
decreases. When a needle valve lifting force based on the pressure in the fuel storage chamber
33
becomes larger than a needle valve lowering force based on the pressure in the balancing chamber, the needle valve
35
moves up, and the injection holes
40
are opened, the injection of the fuel starting. When the solenoid
47
of the solenoid valve
45
is then deenergized, the valve disc
48
closes the orifice A, and the fuel pressure in the balancing chamber
34
increases instantly by the high-pressure fuel introduced through the orifice B. Consequently, the needle valve
35
lowers, and the injection ports
40
are closed, the injection of the fuel stopping. When the orifice A is dosed by putting the solenoid valve
45
in an OFF-state, to instantly increase the fuel pressure in the balancing chamber
34
, a flow of the fuel leaving the fuel storage chamber
33
, passing through the injection nozzle
39
and injected from the injection ports
40
occurs, and, therefore, the fuel pressure becomes gradually low toward the lower end of the injection nozzle
39
due to the resistance of an annular fuel flow passage formed between the smaller-diameter portion
37
of the needle valve
35
and the portion of an inner surface of the casing
31
which is around the same portion
37
of the needle valve. Accordingly, a generally lowering force is exerted on the needle valve
35
on the basis of the high fuel pressure in the balancing chamber
34
, the fuel pressure in the fuel storage chamber
33
and the fuel pressure on the seat
41
, so that the needle valve
35
is closed.
FIG. 9
is a schematic diagram showing a fuel supply system in a conventional accumulator fuel injection apparatus. The orifices A, B are fixed orifices (the inner diameters dA.dB of the orifices A, B are constant), and the orifice A is set larger than the orifice B (dA>dB). Accordingly, a flow rate of a fuel flowing out from the orifice A is determined by the size of the orifice B. The lift of the needle valve
35
attains a peak when an injection rate is not lower than a certain level.
FIG. 10
is a graph showing the relation between the area characteristics of injection holes of an injector used for a diesel engine, i.e. the lift of a needle valve
35
in the injector and an effective opening area of an injection nozzle
39
. Although when the lift is low, i.e., when the lift of the needle valve
35
is low, the effective opening area of the injection nozzle
39
increases in accordance with the size of a clearance between a needle
38
and a seat
41
, when the area of the clearance exceeds that of the injection ports
40
, the effective opening area becomes constant irrespective of the lift of the needle valve
35
.
A conventional example shown in
FIG. 12
is an example (which will hereinafter be referred to as a second conventional example, in which the structural elements equivalent to those of the first conventional example are designated by the same reference numerals, whereby repeated detailed descriptions of the elements are omitted), in which a return spring
52
for exerting a lowering force on a needle valve
35
is provided so that an effect in closing the needle valve
35
is obtained more reliably not by depending upon the flow passage resistance alone when a solenoid valve is in an OFF-state. The needle valve
35
in the second example comprises a larger-diameter portion
36
, a smaller-diameter portion
37
and a diame
Browdy and Neimark
Isuzu Motors Limited
Miller Carl S.
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