Mechanical distributor injection pump having cold-start...

Internal-combustion engines – Charge forming device – With fuel pump

Reexamination Certificate

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Reexamination Certificate

active

06748930

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to distributor injection pumps. More particularly, the present invention relates to a high-pressure pump for supplying fuel to an internal combustion engine.
BACKGROUND INFORMATION
Because of continuously increasing requirements due to stricter exhaust regulations for gasoline engines and compression-ignited internal combustion engines, the point of injection, in particular for compression-ignited internal combustion engines, should be adjusted to the particular operating phase of the engine. In the cold-running phase, in particular at low outside temperatures, the point of injection may need to be advanced at diesel distributor injection pumps, thus making a low-emission start with reduced particle emission and reduced noise, as well as a subsequent emission-free cold-running phase possible. As the rotational speed of the internal combustion engine increases, the delivery start of the injection pump should be advanced in order to compensate for the time shift caused by delayed injection and ignition.
After the injection operation, diesel fuel may require a certain time period to pass from the liquid state into the gaseous state and, in this state, to form an ignitable mixture with the combustion air which self-ignites at high pressure. The time period between the injection start and combustion start is discussed in regards to compression-ignited internal combustion engines as ignition delay. The ignition delay is determined, among other factors, by the ignitability of the diesel fuel (expressed by the cetane number), the achievable compression ratio &egr; of the compression-ignited internal combustion engine, and the quality of the fuel atomization by the injection nozzle of the fuel injector. The ignition delay of compression-ignited internal combustion engines is usually on the order of magnitude of 1 to 2 ms. During the cold-running phase at low outside temperatures, this time period becomes longer, resulting in soot production by the uncombusted fuel, which is discharged into the environment through the exhaust system.
In the case of distributor injection pumps of compression-ignited engines, different cold-start acceleration measures may be used. A hydraulic measure for start acceleration is to temporarily raise the internal pressure of the distributor injection pump during the cold start and during the immediately subsequent cold-running phase of compression-ignited internal combustion engines. As the internal pressure is raised, an injection start timing piston is displaced, resulting in the injection start being advanced. The disadvantage of this measure may be the subsequent loose run of the injection timing piston due to the slow increase in pressure in the interior of the distributor injection pump.
Another option for advancing the injection start is to advance the injection timing piston and thus the injection start by rotating a component designed as a roller ring during the start and during the cold-running phase of the compression-ignited internal combustion engine. Another measure for cold start acceleration which may be carried out using mechanical means is to displace the injection timing piston by pressing on one side of the injection timing piston using a cam shaft so that the injection start is advanced.
The above-mentioned measures may have the disadvantage that only a small amount of adjustment is possible, limited by the mechanical overstress of the components involved, and thus only a limited advance of the injection start is achievable.
FIG. 1
shows a high-pressure pump having an advance timing unit, as is conventional in the related art.
High-pressure pump
1
includes a housing
2
, on whose lower side a timing unit
5
for displacing the point of injection is flange-connected. Timing unit
5
for displacing the point of injection includes a two-part housing, a gasket plate being inserted at a housing joint
40
between the halves of the housing of timing unit
5
and housing
2
of high-pressure pump
1
.
Timing unit
5
for displacing the point of injection includes a displaceably mounted injection timing piston
6
. A pivot bearing
7
, which is used to receive a lever, is positioned inside injection timing piston
6
. Using this lever, a roller ring of a high-pressure pump
1
may be adjusted within housing
2
in such a manner that the point of injection of fuel into the combustion chambers of an internal combustion engine is displaced.
This lever is also referred to as a timing pin of an injection timing piston for adjusting the roller ring.
The lever accommodated in pivot bearing
7
of injection timing piston
6
extends through an orifice
9
in the injection timing piston, which is dimensioned in such a manner that a pivoting movement of the lever of pivot bearing
7
within injection timing piston
6
is possible. Injection timing piston
6
is penetrated by a first inlet bore
10
, which may run essentially in the vertical direction, and a second inlet bore
11
, which may run essentially perpendicular to the first bore. Second inlet bore
11
discharges into a regulating slide bore
13
, which may run essentially parallel to the axis of symmetry of injection timing piston
6
. A piston-shaped regulating slide
12
, which is provided on its face toward a cavity
24
with an outlet bore having an enlarged diameter, is introduced into regulating slide bore
13
. Regulating slide
12
corresponds to a control piston and is also referred to in combination with injection timing piston
6
as a trailing or servo injection timing piston. There is a connection between a first channel
14
, running transversely to the axis of symmetry of regulating slide
12
, and a second channel
15
implemented in regulating slide
12
, second channel
15
discharging in the region of regulating slide
12
which is implemented with an enlarged internal diameter. A slotted disk
16
is assigned to regulating slide
12
on its external circumference, which fixes the displacement path of regulating slide
12
running in the axial direction inside injection timing piston
6
, the slotted disk forming a stop
22
for regulating slide
12
.
Slotted disk
16
presses against second front face
18
of injection timing piston
6
inside a recess
19
of injection timing piston
6
, while, in the state illustrated in
FIG. 1
, first front face
17
of injection timing piston
6
faces a housing delimitation wall of timing unit
5
for displacing the point of injection.
On its face toward a cavity
24
, regulating slide
12
includes a support disk
20
, which is used as a contact surface for a control spring
31
. Control spring
31
is supported on inner side
26
of a cold-start accelerator piston
23
. A disk
21
may be provided on inner side
26
of cold-start accelerator piston
23
. Inner side
26
of cold-start accelerator piston
23
is additionally used as a stop surface for a first spring element
25
, which is supported on an adapter plate
30
on the side diametrically opposed to inner side
26
. An annular projection is implemented on adapter plate
30
, which is used as a stop surface for second front face
18
of injection timing piston
6
. In addition, a trailing piston/regulating slide retaining spring
32
is introduced between first spring element
25
and control spring
31
. This retaining spring is supported on one side on the peripheral surface of slotted disk
16
on second front face
18
of injection timing piston
6
and on the other side on a sleeve body
34
. Sleeve body
34
, whose lateral surface includes individual orifices
35
, has a first sleeve body stop
36
and a second sleeve body stop
37
. Regulating slide/trailing piston retaining spring
32
is supported on one side on first sleeve body stop
36
and on the other side on slotted disk
16
in the region of second front face
18
of injection timing piston
6
.
Face
27
of cold-start accelerator piston
23
illustrated here, which faces a pressure chamber
28
, is supported on a stop
29
implemented on the housing wall o

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