Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1991-11-22
1993-03-16
Cross, E. Rollins
Internal-combustion engines
Charge forming device
Fuel injection system
123500, F02M 3704, F02M 5702
Patent
active
051935074
DESCRIPTION:
BRIEF SUMMARY
RELATED PATENT APPLICATION
This invention relates to PCT/DE 91/00179 filed Mar. 1, 1991.
The invention relates to a fuel injection device for fuel-injected internal combustion engines, in particular to a unit fuel injector, in which the control of the onset and end of supply is effected by means of a magnet valve incorporated between a low-pressure circuit and a work chamber of a pump piston; a scavenging bore, connectable to the work chamber, of a scavenging line that communicates with a low-pressure chamber or the tank is provided, and a delivery line for delivering the fuel from the magnet valve to the work chamber of the pump piston discharges directly into the pump work chamber and communicates with it in a permanently open fashion.
Particularly when the injection device is put into operation or if there is some malfunction in fuel delivery, there are air inclusions or gas bubbles in the work chamber of the piston and in the lines; when relief suddenly occurs at the end of injection, these inclusions and bubbles implode and cause cavitation and erosion of the pistons and conduits; they also impair the stability of the injection. Scavenging is intended to flush away these air inclusions or gas bubbles from the critical regions, to avoid destruction of the surfaces. Such embodiments of an injection device are known, for instance from European Patent Document A 0 207 652. There, however, the work chamber of the piston is located in a shunt around the scavenging flow, impairing the scavenging effectiveness. This known embodiment also requires a large number of conduits and control grooves, which creates idle spaces that have a harmful effect, particularly at the high injection pressures used today, of 1200 to 1600 bar, for instance. Satisfactory scavenging is therefore not attained in this known embodiment.
The object of the invention is to improve the scavenging.
The invention therefore resides substantially in that the mouth of the scavenging bore is located in a region of the guide bore of the pump piston which is overridden by the pump piston in all the positions of the pump piston, and that this mouth is connectable at least indirectly to the delivery line and the work chambers of the pump piston, via a recess of the piston, in the region of the top dead center position of the piston. Since the mouth of this scavenging bore is located in the region of the piston guide bore overridden by the piston, it is closed off until such time as the recess overrides this guide bore. Since this recess overrides the scavenging bore in the top dead center position of the piston, the scavenging bore is uncovered in the top dead center position, and the scavenging ensues. Since the delivery line or its connecting bore communicates in a permanently open fashion with the pump work chamber, the scavenging flow now takes place via the pump work chamber as soon as the recess opens the scavenging bore, so that the pump work chamber is scavenged effectively. It is advantageous if the cam has a circular-cylindrical zone in the region of its highest lobe, and the center of the radius of curvature of this zone coincides with the center of the camshaft, so that the scavenging bore is kept open for the duration of scavenging.
According to features set forth herein, the arrangement is advantageously selected such that a delivery bore forming part of the delivery line from the magnet valve to the work chamber discharges into the guide bore in a region of the guide bore of the piston that is overridden by the recess in the region of the top dead center position of the piston, and a connecting bore communicating openly with the work chamber branches off from the guide bore near the mouth thereof into the guide bore of the piston, the recess of the piston being preferably embodied as an annular groove.
According to additional features, the recess or annular groove of the pump piston may also communicate openly with the work chamber thereof via a relief line provided in the piston. Accordingly, the relief line in the pump piston may
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Cross E. Rollins
Greigg Edwin E.
Greigg Ronald E.
Moulis Thomas
Robert & Bosch GmbH
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