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Patent Abstract
A solenoid valve valve part for controlling a fuel injector in a
fuel injection system has a valve needle, the open and closed positions
of which may be controlled by the solenoid valve valve part. The
solenoid valve valve part has a valve ball which rests on a valve
seat and which lifts up from the valve seat when current flows through
the solenoid valve valve part. The valve seat is in hydraulic connection
with the fuel injector via a borehole. When the valve ball lifts
up from the valve seat, a pressure medium such as high-pressure
fuel flows through the borehole into a pressure relief chamber in
the solenoid valve valve part. In the further progression this causes
the fuel injector to open. To prevent the formation of cavitation
bubbles and the damage thus caused, the borehole includes, at least
in part, one or more sections having a cross section which continuously
expands in the direction of the valve seat. A separation in flow
brought about by sharp transition edges, which may cause cavitation
bubbles, is thus counteracted.
Patent Claims
What is claimed is:
1. A solenoid valve for controlling a fuel injector in a fuel injector
system, comprising: a valve seat of a pressure relief chamber; and
a valve ball arranged on the valve seat; wherein a borehole hydraulically
connects the valve seat to a control pressure chamber of the fuel
injector, the borehole including at least one section having a cross
section that continuously expands in a direction of the valve seat.
2. The solenoid valve according to claim 1, wherein the borehole
includes a first section, a second section, and a middle section
merging into one another, a cross section of the middle section
continuously expanding.
3. The solenoid valve according to claim 2, wherein the first and
second sections adjoin the middle section and have lengths that
are substantially the same.
4. The solenoid valve according to claim 1, wherein the borehole
includes two sections having respective cross sections that continuously
expand, and the two sections respectively adjoin another section
having a constant diameter.
5. The solenoid valve according to claim 1, wherein the at least
one section has a conical shape.
6. The solenoid valve according to claim 1, wherein aperture angles
of successive sections of the borehole increase in the direction
of the valve seat.
7. The solenoid valve according to claim 1, wherein the at least
one section is manufactured by rounding off two borehole transitions.
Patent Description
FIELD OF THE INVENTION
[0001] The present invention relates to a solenoid valve for controlling
a fuel injector.
BACKGROUND INFORMATION
[0002] Solenoid valves are used to control fuel injectors in a
fuel injection system having a valve needle, the open and closed
positions of which may be controlled by the solenoid valve.
[0003] The solenoid valve has a valve ball, which lifts up and
opens a valve seat when current flows through the magnet assembly
of the solenoid valve. This valve seat is in hydraulic connection
with the control pressure chamber of the fuel injector via a borehole.
When the valve seat opens, the pressure in the pressure chamber
of the fuel injector drops, and the fluid (pressure medium) flows
through the borehole in the direction of the valve seat and further
into a pressure relief chamber. This causes the valve needle or
the fuel injector to open.
[0004] It is believed that the common rail injector (CRI) operates
according to this conventional operating principle, which permits
a main injection and a pilot injection having very brief injection
times. Such a solenoid valve is referred to, for example, in German
Published Patent Application No. 196 50 865.
[0005] Cavitation may cause severe damage to the valve seat of
the valve part. The borehole extending through the valve part includes
a cylindrical A-throttle adjoining a pilot borehole in the control
pressure chamber of the fuel injector, and a subsequent cylindrical
diffuser bore leading to the valve seat. The cavitation damage may,
for example, occur in the region of an abrupt transition from the
diffuser bore to the valve seat. This damage may cause "washout"
of the seat edge. As the damage increases, this edge may break off,
resulting in total failure of the injector and operational failure
of the vehicle. To solve this problem, the formation of cavitation
bubbles should be reduced, and the site of implosion of any remaining
bubbles should be shifted to a location, such that this effect no
longer influences the correct functioning of the injector.
SUMMARY
[0006] An exemplary solenoid valve according to the present invention
includes a borehole which has, at least in part, one or more sections
having a cross section that continuously expands in the direction
of the valve seat. Sharp-edged transitions within the borehole,
for example, in the transition region from the A-throttle to the
diffuser bore, may thus be avoided. It is believed that a conical
geometry of the expanding section is advantageous.
[0007] A severe separation in flow may occur when the fluid (pressure
medium) flows through the A-throttle to the outlet edge downstream,
which is sharp-edged due to the manufacturing process, toward the
diffuser bore. Dead water and recirculation areas may form at those
locations. These effects may result in fluctuations in the reproducibility
of the amount of fluid flowing through, as well as in the formation
of zones at partial vacuum and cavitation bubbles.
[0008] Further within the borehole, the flow again contacts the
bore walls. Shortly before reaching the throttle point at the valve
seat situated further downstream, the pressure in the medium rises
again and the cavitation bubbles floating in the liquid stream implode,
thereby causing the described cavitation damage at the wall of the
flow channel.
[0009] As a result of the borehole of an exemplary solenoid valve
according to the present invention, the flow geometry in the valve
part is altered, so that a generally turbulence-free transition
of the medium from the A-throttle to the valve seat may be achieved
without the described negative effects.
[0010] The transition from the A-throttle to the diffuser bore
may, for example, be formed with a continuously expanding cross
section, so that the borehole includes three sections that merge
into one another. In this manner, separation of the flow at the
sharp-edged outlet edge may be prevented.
[0011] Furthermore, the borehole, for example, may be divided into
three sections: the A-throttle, the diffuser bore adjoining the
section expanding in cross section, and the diffuser bore, the A-throttle
and the diffuser bore having substantially the same length. It is
believed that, in conventional designs, the A-throttle directly
adjoins the diffuser bore, the latter having a greater length than
the former. In an exemplary embodiment according to the present
invention, both the A-throttle and the diffuser bore may be considerably
shortened, thereby lowering the pressure, for example, in the diffuser
bore. In conjunction with the continuously expanding (e.g., conical)
transition region between the A-throttle and the diffuser bore,
an optimum shape of the flow channel may be obtained, in which no
cavitation bubbles are formed, and no implosions of these bubbles
are observed.
[0012] In another exemplary embodiment according to the present
invention, the borehole upstream from the valve seat has multiple,
for example, conical, sections expanding in the direction of the
valve seat. A good flow pattern may be obtained when each of the
two cylindrical boreholes, e.g., the A-throttle and the diffuser
bore, has a conically shaped section. For example, the length of
the (cylindrical) diffuser bore may be reduced, so that the pressure
rise within the diffuser bore is no longer sufficient to allow the
implosion of any cavitation bubbles that may form. As described
above, the conical sections connecting the cylindrical boreholes
prevent separation of flow and, thus, prevent the cause of cavitation
bubble formation.
[0013] The aperture angles of the successive conical sections in
the direction of the valve seat may, for example, increase, thus
permitting a gradual transition to the aperture angle of the valve
seat. This may create an favorable flow pattern.
[0014] The sections that continuously expand in cross section,
for example, may be created in a simple mechanical fashion by rounding
off the respective transitions between the boreholes, such as the
A-throttle and the diffuser bore. In this manner, the sharp edge
of a transition may be machined during manufacturing to provide
an optimum flow channel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a sectional view through the valve part of a solenoid
valve.
[0016] FIG. 2 is a sectional view through the valve part of an
exemplary solenoid valve according to the present invention.
[0017] FIG. 3 is a sectional view through the valve part of another
exemplary solenoid valve according to the present invention.
DETAILED DESCRIPTION
[0018] FIG. 1 illustrates the valve part 1 of a solenoid valve
for controlling a conventional fuel injector. Borehole 2 leads to
the control pressure chamber of a fuel injector, and is in hydraulic
connection with valve seat 4 of pressure relief chamber 3 in the
solenoid valve via an additional throttle bore. The throttle bore
is formed from A-throttle 6 and subsequent diffuser bore 5, an abrupt
change in cross section occurring between the cylindrical boreholes
at the transition point.
[0019] When current flows through the solenoid valve, a valve ball
(not shown) in pressure relief chamber 3 lifts up from valve seat
4, thereby allowing the pressure in the valve chamber to decrease
in the direction of the valve ball due to the fact that a pressure
medium, for example, high-pressure fuel, flows from borehole 2 via
the throttle bore into pressure relief chamber 3. The pressure drop
thus created in borehole 2 upstream from the adjoining control pressure
chamber causes the valve needle of the fuel injector to open, and
high-pressure fuel is injected.
[0020] As shown in FIG. 1, the structure formed by A-throttle 6
and diffuser bore 5 is referred to as the throttle bore. When fluid
(e.g., pressure medium, for example, high-pressure fuel) flows through
the throttle bore, a separation in the flow occurs at the sharp
edge of the transition from A-throttle 6 to diffuser bore 5. This
results in turbulence and the formation of dead water and recirculation
areas. The shearing of flow causes cavitation bubbles to form, which
are highly compressed in areas of high pressure, resulting in the
risk of implosion. Imploding cavitation bubbles in the vicinity
of the valve seat may cause damage, which, in the further progression,
may result in "washout" of valve seat 4, so that proper
opening and closing of the solenoid valve, and thus of the injector,
may no longer guaranteed.
[0021] FIG. 2 shows an exemplary solenoid valve according to the
present invention in the region of valve seat 4. Identical parts
from FIG. 1 are provided with the same reference numbers in FIG.
2. A section 7 is provided, which has a continuously expanding cross
section in the throttle bore between borehole 2 leading to the control
pressure chamber and pressure relief chamber 3. In this exemplary
embodiment, section 7 is produced by a method that rounds off the
borehole transition between A-throttle 6 and diffuser bore 5. Simultaneously,
both A-throttle 6 and diffuser bore 5 are considerably shortened
in comparison to the conventional design shown in FIG. 1. In this
manner, the flow geometry may be improved, so that cavitation damage
may be avoided to the greatest extent possible. Thus, an exemplary
solenoid valve according to the present invention may have fail-safe
operability.
[0022] FIG. 3 shows another exemplary solenoid valve according
to the present invention in the region of valve seat 4. In this
design, A-throttle 6 again adjoins borehole 2, which leads to the
control pressure chamber of the fuel injector, as a cylindrical
borehole with a considerably reduced cross section. According to
this exemplary embodiment, a first conical section 9 follows at
an aperture angle a and is followed by a cylindrical diffuser bore
10, which is considerably shortened in comparison to earlier embodiments
(see FIG. 1). Diffuser bore 10 is followed by a section 11 having
a conically expanding cross section that opens into valve seat 4.
Conical section 11 has an aperture angle .beta..
[0023] In this exemplary embodiment according to the present invention,
aperture angle a is 50.degree., and angle .beta. is 60.degree..
Overall, the aperture angle of the flow channel is thus successively
expanded to merge into the valve seat. The flow pattern may be very
favorably influenced by this measure. The combination using the
greatly shortened diffuser bore 10 prevents excessive pressure rises,
which may allow any cavitation bubbles present to implode. The complete
profile of the flow channel of borehole 8 is illustrated in FIG.
3, and is denoted by reference number 12.
[0024] The present invention may be used in any given cross section
of a borehole, and the solenoid valve according to the present invention
may include more than two sections having expanding cross sections
within borehole 8. It is believed that the exemplary solenoid valve
illustrated in FIG. 3 may sufficiently prevent cavitation damage,
thus increasing the functional reliability of common rail injectors.
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