FR2554173A1 - Pilot injection device for internal combustion engines - Google Patents

Abstract

FOLLOWING THE INVENTION, THE INJECTION PISTON 2 INCLUDES AT LEAST ONE ADDITIONAL DRILLING 12 WHICH OPENS ON ITS SIDE WALL on the one hand, AND IN THE HIGH PRESSURE GENERATION CHAMBER 8 on the other hand; THIS DRILLING 12 IS LIKELY TO COME IN COINCIDENCE WITH A DRILLING 14 OF THE SHIRT 4 OPENING INSIDE IT AND CONNECTING TO THE LOW PRESSURE FUEL SOURCE, TO INTERRUPT AT A PREDETERMINED INSTANT AND FOR A PREDETERMINED PERIOD. '' CLOSURE OF THE FUEL INLET PORTS IN THIS HIGH PRESSURE CHAMBER 8, THE DISCHARGE OF THE FUEL TO A CORRESPONDING INJECTOR, ASSOCIATED WITH A CYLINDER OF THE INTERNAL COMBUSTION ENGINE. APPLICATION IN PARTICULAR TO FUEL SUPPLY DEVICES FOR COMPRESSION IGNITION THERMAL ENGINES.

Description

PILOT INJECTION DEVICE FOR INTERNAL COMBUSTION ENGINES
The present invention relates to a pilot injection device for an internal combustion engine of the type providing a pre-injection of the fuel charge very early in the cycles with a small quantity and a short injection duration relative to the delay of auto-ignition of the fuel, and a main injection of the additional charge in a warmer and more compressed environment.

 Pilot injection allows ignition of the main injection fuel almost without ignition delay. This results in more progressive combustion, a smoother pressure front in the combustion chamber, and an improvement in thermal efficiency combined with a reduction in the noise emitted by the engine mainly in the vicinity of idling.

 This type of injection thus makes it possible to free oneself from the constraints relating to an introduction rate which must normally remain below a given threshold for a noise limit level.

 Many generally complicated mechanisms have been designed to provide this injection in two phases.

 The present invention proposes an injection device commonly pilot directly derived from the injection devices used, and the additional means of which for obtaining this pre-injection prove to be particularly easy and economical to use.

This pilot injection device according to the invention is of the type comprising a high pressure generation chamber delimited in a chenu se and the volume of which is modified by continuous and alternating movement between two top and bottom neutral positions, of a piston closing during its movement towards top dead center at least one fuel inlet orifice in this chamber thus connected to a fuel source
low pressure, to push the fuel out of this
chamber to an injector associated with an engine cylinder
internal combustion, this piston having means for determining
the start and end of fuel delivery.

According to an advantageous feature of the invention, this
piston has at least one additional hole which opens out
on its side wall on the one hand, and in this upper room
pressure on the other hand 5 this drilling is more likely to
to coincide with a piercing of this emerging shirt
inside it and connected to this bass source near
sion, to interrupt at a predetermined time and for a
duration of time - predetermined after closing the orifices
fuel supply, the delivery of fuel to a
corresponding injector.

These additional means apply to in pumps
in-line element junction, to distributor injection pumps
rotary and injector pumps.

The invention will be better understood during the description
which follows, made with reference to the appended drawings given
solely by way of nonlimiting example to illustrate Sun embodiment of the invention, and in which
- Figure l shows a schematic view in longitu section
dinal and axial of an injection device conforming to
inveation and intended for a single cylinder combustion engine
internal ;;
- Figure 2 shows a schematic view of the above device
tooth in cross section along line 2-2
- Figure 3 shows two trajectories t and td of a
hole in the side wall of an injection piston, obtained 0 <
from the variation of the angular positiong of the crankshaft
as a function of the axial stroke x of the injection piston; and - Figure 4 shows two variation curves of a lift
injector needle h depending on the position of the
engine piston, expressed in angular position zW of the crankshaft,
curve illustrating the fuel delivery.

 FIGS. 1 and 2 schematically show a typical injection device for a single-cylinder internal combustion engine. This device notably comprises a piston 2 driven by a reciprocating and continuous movement inside a jacket 4 between a neutral position. down and a top dead center position. This piston is in contact by its head 6 with a high pressure generation chamber 8 delimited inside this jacket 4 and whose volume is made variable by the displacement of the piston 2. At least one inlet orifice 10 of fuel opens into this chamber 8 so as to allow filling thereof when the piston 2 occupies its bottom dead center position. This orifice 10 therefore connects the chamber 8 to a low pressure fuel source. The piston 2 closes during its movement towards its top dead center position the orifice 10 so as to discharge the fuel out of the chamber 8 towards a injector not shown, associated with the engine cylinder. The piston also has means known per se for determining the start and end of the fuel delivery.

According to the invention, the piston 2 has an additional bore 12 (in the case of a single cylinder) which opens on its side wall on the one hand, and in the high pressure chamber 8 on the other hand, for example axially in the figures l and 2. The additional bore 12 is likely to coincide with a bore 14 made in the jacket 4 where it opens by being connected to the low pressure fuel source
Referring to Figures 3 and 4, the injection device previously described operates as follows
Each geometrical point of the periphery of the piston 2 describes a repetitive trajectory t similar to that represented in FIG. 3J corresponding to the drilling hole 12.

Its position can thus be identified by its curvilinear abscissa s
For the majority of single-phase injection devices, the injection takes place in one go from so to sl. In an injection pump according to the invention, the pre-injection occurs from so to sti, the injector needle resting on its seat in the closed position from s'l to s'2, and the main injection has instead of s'2 to s2.

The space created between the two injection phases is caused by a controlled discharge of the injection flow towards the interior of the pump rather than towards the injector considered.
This phenomenon is repeated of course for each of the cylinders of an engine with n cylinders, case where the injection piston 2 has n additional holes.

 Two fuel delivery phases I and II from the chamber 8 are illustrated in FIG. 4 where the start M of the pre-injection I can be triggered - at an instant corresponding to an angle of rotation C4 (M) of the front crankshaft the top dead center of the cylinder piston, for an idle speed at low engine load where it is useful to reduce the noise emitted.

 The invention advantageously provides the possibility of applying pilot injection only for desired engine operating conditions; in fact, it is easy to eliminate the pre-injection by moving the piston 2 relative to the jacket 4 so as to make it describe an offset relative trajectory td without coincidence of the holes 12 and 14 (cf.

Figure 3), which is also found on curve c of Figure 4 corresponding to a high engine speed at full load.

 Of course, the invention is not limited to the example of embodiment described and shown above, from which other forms and embodiments can be provided, without thereby departing from the scope of the invention. This is particularly the case for injection systems which include a distributor piston which does not generate a high pressure. This piston can therefore receive, as before, at least one additional bore in communication with the high pressure chamber, and capable of coming temporarily into coincidence during the injection phase, with an associated discharge orifice, produced in the jacket of the distributor piston and connected to the low pressure source.

Claims (1)

CLAIMS. 1. Pilot fuel injection device for an internal combustion engine, of the type comprising a high pressure generation chamber delimited in a jacket and the volume of which is modified by continuous and alternating movement between two top dead center positions and bottom, of a piston closing during its movement towards the top dead center at least one fuel inlet orifice in this chamber thus connected to a source of low pressure fuel, for driving the fuel out of this chamber towards an injector associated with a cylinder of this engine, said piston having means for determining the beginning and the end of the fuel delivery, characterized in that this piston (2) comprises at least one additional bore (12) which leads to its side wall on the one hand, and in this high pressure chamber (8) on the other hand, and in that this bore (12) is likely to come into coincidence with a bore (14) of this jacket (4) d boiling inside of it and connected to this low pressure source, to interrupt at a predetermined instant and for a predetermined period of time after shutting off at least one fuel inlet orifice, the discharge of the fuel to a corresponding injector.