Pumps – Expansible chamber type – Electrically or magnetically actuated distributor
Reexamination Certificate
1999-12-21
2002-09-10
Freay, Charles G. (Department: 3746)
Pumps
Expansible chamber type
Electrically or magnetically actuated distributor
C123S446000, C123S447000, C123S456000, C137S614190, C137S614200, C417S439000
Reexamination Certificate
active
06447273
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pump to spray fuel at a high pressure into combustion chambers of an engine and, more particularly, a variable-delivery high-pressure fuel pump to pressurize, meter a fuel and then deliver the metered fuel to the combustion chambers.
2. Description of the Prior Art
For the variable-delivery high-pressure fuel pumps, generally, two types of pumps have been developed one of that is a high-pressure fuel pump
80
of inlet port-metering system, as shown in FIG.
9
. It has an inlet port valve
81
for regulating an inflow rate of fuel into a cylinder to control a metered amount of fuel discharged. The other is a high-pressure fuel pump
90
of a system that is termed pre-stroke control, as shown in
FIG. 10
, where an inlet port valve
91
is controlled according to the pre-stroke way.
The high-pressure fuel pump
80
shown in
FIG. 9
is a type of fuel pump to spray the pressurized fuel at a high pressure into the combustion chambers of the engine, in which a fuel introduced through a fuel inlet passage
82
when the inlet port valve
81
is kept open is pressurized in a pump chamber
85
by the action of a reciprocating pump plunger
84
actuated by an eccentric cam
83
, which is driven by a power-take-off shaft of the engine. The pressurized fuel is then delivered to either a common fuel rail or injectors through a fuel discharge passage
86
. According to the type as described just above, the metered amount of fuel discharged is determined depending on the inflow rate of fuel that flows through a valve seat for a pre-selected time during which the inlet port valve
81
is kept open.
In contrast, the high-pressure fuel pump
90
illustrated in
FIG. 10
operates with such systems that the inlet port valve remains open after the bottom top center of the pump plunger for a short time of delay until a volume confined between the pump plunger and its associated cylinder reaches a desired amount of fuel to be discharged. The instant the desired amount of fuel is reached in the pump chamber, the inlet port valve is closed and the metered amount of fuel, which has been trapped in the pump chamber defined by the cylinder on the plunger, is delivered out of the pump chamber. Thus, excess fuel in the pump chamber is left returned through the inlet port valve until the pump chamber defined by the cylinder on the plunger is made reduced in volume to the desired amount of fuel to be discharged.
In the high-pressure fuel pump
90
, the plunger
94
moves up and down as a cam
93
rotates, thereby varying the volume in the pump chamber
95
. On descendent movement of the plunger
94
, the pump chamber
95
is increased in volume while reduced in pressure, resulting in opening the inlet port valve
91
of a solenoid-actuated valve to admit the fuel into the pump chamber through a fuel inlet line
92
. The inflowing fuel is not under the high pressure, but at a relatively low-pressure anticipated by a low-pressure supply pump. The pump chamber is initially sufficient large in volume compared with the desired amount of fuel to be discharged. As the cam
93
starts to rotate, the plunger
94
lifts to reduce the pump chamber
95
in its volume with the inlet port valve
91
still remaining open. Thus, the fuel admitted in the pump chamber
95
is partly forced to return through the inlet port valve
91
to the fuel inlet passage
92
. The instant the amount of fuel in the pump chamber
95
has reached the desired amount of fuel, the inlet port valve
91
is closed. Thereafter as the plunger
94
continues to move upwardly, the fuel metered in the pump chamber
95
is forcible discharged to a fuel delivery port
96
.
Disclosed in Japanese Patent Laid-Open No. 257533/1994 is a prior fuel-injection pump of pre-stroke control system, in which a back-pressure chamber supplied with a low-pressure fuel is provided behind a main valve body partly forming walls of a pump chamber. The fuel pressure in the back-pressure chamber is controlled by opening and closing between the back-pressure chamber and a subsidiary valve chamber by the action of a solenoid-actuated subsidiary valve, which is held for sliding movement in the subsidiary valve chamber. A piston section of the main valve body moves in a reciprocating manner in compliance with the combination of an urging force of a main valve spring and a pressure difference between the back-pressure chamber and an area in a main valve chamber, which communicates with a fuel passage or is exposed to the pump chamber, to thereby let the main valve body open and close between the back-pressure chamber and the subsidiary valve chamber. No fuel in the pump chamber is discharged backwards to the fuel passage at an earlier portion of lift of the plunger. Energization of the solenoid-actuated valve, nevertheless, regulates the timing for closure of the main valve body that allows the pressure to escape from the back-pressure chamber. This controls the effective stroke of the plunger after the back-pressure chamber has been disconnected from the pump chamber in a compressively forcing phase of the plunger.
Another conventional high-pressure fuel-injection pump of pre-stroke control system is disclosed in Japanese Patent No. 2,690,734. In accordance with this prior high-pressure fuel-injection pump, electric conduction of a solenoid-actuated valve makes a valve body block up a passage formed between the valve body and its valve seat for interconnecting a pump chamber with a low-pressure passage. Fuel in the pump chamber is raised in pressure by means of a compression member and then discharged to a common fuel-rail through a delivery port. Varying an electric conductive duration to the solenoid-actuated valve results in controlling the amount of fuel delivered to the common fuel-rail. The solenoid-actuated valve includes an outwardly-opening poppet-type valve body that is exposed at its entire lower surface against the pressure created in the pump chamber. Thus, the fuel pressure created in the pump chamber acts on the valve body as a motive force to effectively urge the valve body against its valve seat at closure event, in addition to the electromagnetic attractive force of the solenoid-actuated valve, to thereby aid the solenoid-actuated valve in ensuring the intensified closure power, resulting in keeping the pressure against any leakage past the valve at the closure event.
With most high-pressure fuel pumps of inlet port-metering system, on the other hand, a negative pressure developed ahead of the inlet port valve raises a major disadvantage of unsteady operation of the inlet port valve, which might occur due to cavitation or a sudden change in pressure. It has been thus required to eliminate the possible negative pressure ahead of the inlet port valve or keep the pressure ahead of the valve on any positive pressure. This, however, makes the inlet port valve complicated in structure. In conventional flow rate control of pre-stroke system to drive directly the inlet port valve connecting the pump chamber with the low-pressure side, moreover, the inlet port valve has to be actuated against the fuel pressure elevated up to a high pressure in the pump chamber and, therefore, it is inevitably required to make large the elastic force of a spring and the electromagnetic force of a solenoid-actuated valve to operate the inlet port valve. This leads to the large size of the solenoid-actuated valve, which might contribute to plague drawbacks of noise pollution and power-hungry consumption. In contrast, where the inlet port valve is operated, indirectly with making use of the low pressure fuel, by the energization of the solenoid-actuated valve, a control mechanism of using the low-pressure fuel is arranged between the solenoid-actuated valve and the inlet port valve. This design may likewise result in a bulky high-pressure fuel pump. With either system of direct or indirect operation of the inlet port valve, the drawbacks are the same as described just above: the solenoid-actuated valv
Hidaka Shoshi
Nishimura Terukazu
Browdy and Neimark , P.L.L.C.
Freay Charles G.
Isuzu Motors Limited
Rodriguez William H.
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