Internal-combustion engines – Combustion chamber means having fuel injection only – Using multiple injectors or injections
Reexamination Certificate
2000-06-19
2002-03-26
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Using multiple injectors or injections
C123S575000
Reexamination Certificate
active
06360714
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a fuel injector, and particularly to a pressure accumulator type fuel injector having superior responsiveness of fuel pressure control.
2. Prior Art
To improve engine performance over a wide engine operating range extending from low speeds to high speeds, diesel engines have been fitted with pressure accumulator type fuel injection systems (common rail systems) capable of supplying high-pressure fuel stored in an accumulator in a stable manner to each cylinder of the engine.
However, even when this kind of fuel injection system is used, sudden explosive combustion occurs near the start of combustion when the fuel injection rate immediately after the start of fuel injection in the fuel injection cycle is excessively large, which results not only in an increase in engine noise, but also in an increase in the amount of oxides of nitrogen (NOx) in the exhaust gas.
To eliminate this kind of problem, common rail fuel injection systems which start fuel injection at a somewhat low fuel injection rate in an initial stage of the fuel injection cycle have been proposed.
As shown in
FIG. 7
, this kind of common rail fuel injection system
1
has a high-pressure common rail
2
storing high-pressure fuel pressurized by a fuel pump
1
a
, a low-pressure common rail
7
storing fuel at a lower pressure than the high-pressure fuel in the high-pressure common rail
2
, and a fuel injection valve
3
for injecting high-pressure fuel from the high-pressure common rail
2
and low-pressure fuel from the low-pressure common rail
7
into a combustion chamber of the engine. The fuel injection valve
3
is connected to the high-pressure common rail
2
by a fuel supply pipe
11
. The fuel injection valve
3
has inside it a pressure control chamber
3
a
and a fuel chamber
3
b
connected to the fuel supply pipe
11
, and has a closing valve
15
for fuel injection timing control interposed between the pressure control chamber
3
a
and a fuel discharge conduit (not shown).
A pressure-switching valve
4
is provided in the fuel supply pipe
11
, and a branch fuel pipe
12
branches from the fuel supply pipe
11
on the downstream side of this pressure-switching valve
4
. The branch fuel pipe
12
includes two mutually parallel conduit sections, in one of which an orifice
5
is disposed and in the other of which a check valve
6
is disposed, and the low-pressure common rail
7
is connected to the fuel supply pipe
11
by this branch fuel pipe
12
. Also, an electromagnetic pressure control valve
8
for controlling the fuel pressure of the low-pressure common rail
7
to a predetermined fuel pressure lower than that of the high-pressure fuel in the high-pressure common rail
2
is provided in a fuel return pipe
7
a
extending between the low-pressure common rail
7
and a fuel tank
10
.
The check valve
6
thus has one side connected to the low-pressure common rail
7
and the other side connected by the branch fuel pipe
12
to the fuel supply pipe
11
downstream of the pressure-switching valve
4
. As shown in
FIG. 8
, the check valve
6
has a valve member
17
received in a cylindrical housing
16
and a spring
18
urging the valve member
17
in its closing direction. This check valve
6
is constructed to open and allow a flow of fuel from the low-pressure common rail
7
to the fuel supply pipe
11
when the fuel pressure in the low-pressure common rail
7
rises above the sum of the fuel pressure in the fuel supply pipe
11
and the urging force of the spring
18
. In
FIG. 8
, the reference numeral
19
denotes a spring receiving part and the reference numeral
16
a
a valve seat part.
In the fuel injection system of
FIG. 7
, until a fuel injection start time is reached, both the pressure-switching valve
4
and the closing valve
15
are kept closed, and the connection between the fuel injection valve
3
and the high-pressure common rail
2
and the connection between the pressure control chamber
3
a
and the fuel discharge conduit are cut off. In this state, due to the action of the orifice
5
and the check valve
6
, the fuel in the fuel supply pipe
11
downstream of the pressure-switching valve
4
and the low-pressure fuel in the low-pressure common rail
7
are at the same pressure, and consequently low-pressure fuel from the fuel supply pipe
11
is supplied to the pressure control chamber
3
a
and the fuel chamber
3
b
of the fuel injection valve
3
.
When the fuel injection start time is reached, the closing valve
15
is opened and fuel in the pressure control chamber
3
a
is discharged through the fuel discharge conduit. This causes a fuel pressure pushing a needle valve
3
c
in its closing direction to fall, and consequently the needle valve
3
c
is moved in its opening direction by the fuel pressure of the fuel chamber
3
b
against the urging force of a return spring
3
d
urging it in its closing direction, and the fuel injection valve
3
opens and a low-pressure initial injection (hereinafter, ‘low-pressure injection’), wherein low-pressure fuel in the fuel chamber
3
b
is injected, is carried out. When the low-pressure injection period elapses, the pressure-switching valve
4
is opened and high-pressure fuel from the high-pressure common rail
2
is supplied through the fuel supply pipe
11
to the fuel chamber
3
b
, and a high-pressure main injection (hereinafter, ‘high-pressure injection’), wherein high-pressure fuel is injected, is carried out following the low-pressure injection. Next, when an injection end time is reached, the closing valve
15
is closed and the connection between the pressure control chamber
3
a
and the fuel discharge conduit is cut off, the fuel pressure in the pressure control chamber
3
a
rises, the pushing force pushing the needle valve
3
c
in its closing direction increases, and the fuel injection valve
3
closes. Also, the pressure-switching valve
4
is closed, and high-pressure fuel in the fuel supply pipe
11
flows into the low-pressure common rail
7
through the orifice
5
. When the fuel pressure in the low-pressure common rail
7
rises, the pressure control valve
8
is duty-controlled so that the fuel pressure in the low-pressure common rail
7
assumes a predetermined fuel pressure lower than that of the high-pressure fuel, and some of the fuel in the low-pressure common rail
7
is discharged to the fuel tank
10
as necessary.
In this way, the common rail fuel injection system
1
switches the fuel injection waveform from a low pressure to a high pressure by operating the pressure-switching valve
4
during the fuel injection period, i.e. the period for which the closing valve
15
is open, and in an initial stage of fuel injection, because a low-pressure injection is carried out, combustion is effected relatively slowly and the amount of NOx emissions in the exhaust gas is reduced. Also, because a high-pressure injection is being carried out at the end of fuel injection, the fuel injection rate falls rapidly as soon as the closing valve
15
closes, and the emission of smoke and particulates is reduced.
This common rail fuel injection system
1
of the related art includes the fuel supply pipe
11
extending between the fuel injection valve
3
and the pressure-switching valve
4
and the branch fuel pipe
12
extending between the fuel supply pipe
11
and the low-pressure common rail
7
. Consequently, the fuel injection system
1
as a whole occupies a large space and has poor ease of mounting to the engine. In particular, when the fuel injection valve is to be mounted over the center of the combustion chamber on a four-valve/cylinder diesel engine having two intake valves and two exhaust valves per cylinder, the installation space for the fuel injector on the cylinder head
71
is narrow and it is essential for a fuel injector to be mounted on this kind of engine to be made compact.
Also, the lengths of the fuel supply pipe
11
and the branch fuel pipe
12
are long, and the internal volumes of the fuel supply pipe
1
Kohketsu Susumu
Kotooka Seijiro
Tanabe Keiki
Miller Carl S.
Mitsubishi Jidosha Kogyo Kabushiki Kaisha
Rossi & Associates
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