Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2001-11-27
2003-09-23
Moulis, Thomas N. (Department: 3748)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S514000
Reexamination Certificate
active
06622701
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to an accumulator fuel injection system for internal combustion engines, and more particularly to an improved structure of such a system designed to avoid a failure in operation of a pressure relief valve caused by pressure pulsations of a drain line.
2. Background Art
Accumulator fuel injection systems are known which supplies a high-pressure fuel to an accumulator of a common rail through a supply pump and distributes the fuel stored in the accumulator to a plurality of fuel injectors installed one in each cylinder of an internal combustion engine. The accumulator fuel injection systems usually have a pressure relief valve connected to the accumulator of the common rail.
FIG. 7
shows an example of such a pressure relief valve.
The pressure relief valve
100
works as a pressure limiter and consists essentially of a valve
101
, a cylindrical housing
102
, and a hollow screw
103
. The valve
101
is made up of a valve body having a valve hole
111
formed therein and a valve ball
105
selectively opening and closing the valve hole
111
.
The housing
102
has an inlet side fuel hole
112
, a small-diameter hole
113
, and an outlet side fuel hole
114
. Within the inlet side fuel hole
112
, a spring guide
107
and a spring
108
are disposed which urge the valve ball
105
to close the valve hole
111
at all times. The hollow screw
103
has formed therein a longitudinal hole
115
communicating with the outlet side fuel hole
114
and a lateral hole
116
extending perpendicular to the longitudinal hole
115
. The lateral hole
116
communicates with a fuel passage
117
in a low-pressure pipe
109
(i.e., a drain line) through which the fuel is returned back to a fuel tank (not shown).
A valve-opening pressure at which the ball valve
105
is to be opened is determined by a contact area between the valve body
104
and the valve ball
105
and a set load produced by the spring
108
. The valve-opening pressure may be adjusted by changing the thickness of shims
118
and
119
. The lateral hole
116
of the hollow screw
103
has a fuel-flowing sectional area substantially identical with that between the valve
101
and the longitudinal hole
115
of the hollow screw
103
.
If some flow resistance exists in the low-pressure pipe
109
, it may cause pressure pulsations of the fuel returned from the supply pump or the fuel injector back to the fuel tank through the low-pressure pipe to be transmitted to the valve
101
of the pressure relief valve
100
, so that the valve ball
105
bounces within the valve body
104
, thereby resulting in a change in valve-opening pressure of the pressure relief valve
100
.
SUMMARY OF THE INVENTION
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide an improved structure of an accumulator fuel injection system capable of avoiding a failure of a pressure relief valve caused by pressure pulsations occurring in a drain line.
According to one aspect of the invention, there is provided an accumulator fuel injection apparatus which may be employed in a common rail system for diesel engines. The accumulator fuel injection apparatus comprises: (a) a high-pressure supply pump pumping fuel out of a fuel tank, the high-pressure supply pump pressuring and discharging the fuel; (b) an accumulator storing therein the fuel discharged from the high-pressure supply pump; (c) a fuel injector injecting the fuel stored in the accumulator into an internal combustion engine; (d) a high-pressure fuel line extending from the high-pressure supply pump to the fuel injector through the accumulator; (e) a relief valve having an inlet communicating with the high-pressure fuel line, an outlet, and a valve mechanism disposed between the inlet and the outlet, the valve mechanism being responsive to a rise in pressure of the fuel within the high-pressure fuel line beyond a given level to establish communication between the inlet and the outlet for relieving the rise in pressure of the fuel within the high-pressure fuel line; and (f) a pressure pulsation absorbing mechanism disposed between the valve mechanism of the relief valve and a pressure pulsation source existing downstream of the outlet of the relief valve. The pressure pulsation absorbing mechanism works to absorb a pressure pulsation propagated from the pressure pulsation source to the valve mechanism of the relief valve, thereby avoiding an undesirable change in a valve-opening pressure at which the valve mechanism opens the inlet to drain the fuel within the accumulator.
In the preferred mode of the invention, the valve mechanism includes a valve body in which the inlet of the relief valve is formed and a valve member movable to open and close the inlet selectively. The relief valve includes a hollow cylindrical housing having a fuel hole formed between the inlet and the outlet. The pressure pulsation absorbing mechanism includes a hollow screw which is fitted in an open end of the housing as defining the outlet of the relief valve and has formed therein an orifice working to absorb the pressure pulsation to be propagated from the pressure pulsation source to the valve mechanism. A valve-urging mechanism is disposed in the fuel hole of the housing which urges the valve member to close the inlet constantly.
The hollow screw includes a sleeve and a flange head. The sleeve is retained within the open end of the housing and has formed therein a longitudinal chamber communicating with the fuel hole of the housing through an end of the sleeve. The flange head is formed on an end of the sleeve opposite the housing.
The orifice is implemented by a hole formed in the sleeve which extends perpendicular to the longitudinal chamber of the sleeve. The hole is smaller in diameter than the fuel hole of the housing and the longitudinal chamber of the sleeve.
The relief valve communicates at the inlet thereof with the accumulator for relieving a rise in pressure of the fuel within the accumulator beyond the given level to keep the pressure in the accumulator constant.
The relief valve may alternatively communicate at the inlet thereof with an outlet of the high-pressure supply pump for relieving a rise in pressure of the fuel flowing into the accumulator beyond the given level to keep the pressure of the fuel supplied to the accumulator constant.
The relief valve may alternatively communicate at the inlet thereof with a portion of the high-pressure fuel line extending from the accumulator to the fuel injector for relieving a rise in pressure of the fuel supplied to the fuel injector beyond the given level to keep the pressure of the fuel supplied to the fuel injector constant.
According to another aspect of the invention, there is provided an accumulator fuel injection apparatus which comprises: (a) a high-pressure supply pump pumping fuel out of a fuel tank, the high-pressure supply pump pressuring and discharging the fuel; (b) an accumulator storing therein the fuel discharged from the high-pressure supply pump; (c) a fuel injector injecting the fuel stored in the common rail into an internal combustion engine; (d) a high-pressure fuel line extending from the high-pressure supply pump to the fuel injector through the accumulator; (e) a relief valve having an inlet communicating with the high-pressure fuel line, an outlet, and a valve mechanism disposed between the inlet and the outlet, the valve mechanism being responsive to a rise in pressure of the fuel within the high-pressure fuel line beyond a given level to establish communication between the inlet and the outlet for relieving the rise in pressure of the fuel within the high-pressure fuel line; and (f) a check valve disposed between the valve mechanism of the relief valve and a pressure pulsation source existing downstream of the outlet of the relief valve. The check valve works to block transmission of a pressure pulsation from the pressure pulsation source to the val
Denso Corporation
Moulis Thomas N.
Nixon & Vanderhye P.C.
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