Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1996-10-25
1998-01-27
Moulis, Thomas N.
Internal-combustion engines
Charge forming device
Fuel injection system
123467, F02M 4100
Patent
active
057112746
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention is based on a fuel injection system for internal combustion engines. In one such fuel injection system, known from the professional 1992, pp. 28-30, a high-pressure feed pump fills a high-pressure reservoir with fuel from a supply tank. From the high-pressure reservoir (common rail), pressure lines lead to the various injection valves that protrude into the combustion chamber of the engine to be supplied; in the known system, these valves discharge via a first conduit directly into a first pressure chamber that urges the valve member of the injection valve in the opening direction, and via a second conduit they can be made to communicate with a second pressure chamber, forming a control chamber, that urges the valve member in the closing direction. A 3/2-way control valve is inserted into this second conduit and connects the control chamber at the valve member with the pressure line that begins at the high-pressure reservoir, or with a relief line to the supply tank.
The 3/2-way control valve is actuated by a magnet valve, which is triggered by an electronic control unit that processes various operating parameters of the engine.
The injection valve is kept closed by the communication of the control chamber with the high-pressure reservoir; for that purpose, the pressure engagement face of the valve member that protrudes into the control chamber is embodied as larger than the pressure engagement face protruding into the first pressure chamber, in the opening direction.
If an injection is to take place at the injection valve, then the control valve connects the control chamber to the relief line, so that the high pressure in the control chamber is relieved via this line into the supply tank; to control the course of injection, a throttle is also provided in the relief line. The pressure reduction in the control chamber, as a consequence of the pressure in the first pressure chamber that communicates constantly with the common rail, effects an opening stroke motion of the valve member, so that an injection cross section is opened at the injection valve, by way of which the fuel is injected at high pressure into the combustion chamber of the engine. The injection is terminated by switching the control valve over again and connecting the control chamber to the common rail, in the course of which the high fuel pressure builds up again in the control chamber, so that the valve member is displaced back into its closing position.
The known fuel injection system has the disadvantage, however, that the high fuel pressure remains in the system for a long time even after the engine has been turned off; this makes maintenance and repair work quite dangerous, so that the known system does not meet the usual demands for safety.
ADVANTAGES OF THE INVENTION
The method according to the invention for reducing the fuel pressure in a fuel injection system has the advantage over the prior art that it is possible to drop the high pressure in the common rail and the system communicating with it to a slight, harmless pressure level after the engine has been shut off. This is done by means of components already present in the system, so that in contrast to other versions, no additional pressure valve and no further line is needed, which in particular reduces the effort involved in production and hence the cost for the injection system.
The pressure relief is advantageously effected via the control valve and the pressure chambers of the injection valve into the supply tank; for this purpose, only a single further triggering capability of the magnet valve that actuates the control valve on the electronic control unit after the engine is shut off needs to be provided. The triggering of the control valve is then done so briefly that the pressure required to lift the valve member cannot build up at the injection valve. Depending on the structural design, this is accomplished either by briefly relieving the pressure of the control chamber at the valve member or by briefly imposing pressure on the pressure chamb
REFERENCES:
patent: 4782808 (1988-11-01), Bostick et al.
patent: 5074272 (1991-12-01), Bostick et al.
patent: 5159911 (1992-11-01), Williams et al.
patent: 5408970 (1995-04-01), Burkhard et al.
patent: 5441029 (1995-08-01), Hlousek
Greigg Edwin E.
Greigg Ronald E.
Moulis Thomas N.
Robert & Bosch GmbH
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