Internal-combustion engines – Accessories – Covers – trays – vibrators – corrosion inhibitors – air filters
Reexamination Certificate
1999-12-17
2001-02-27
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Accessories
Covers, trays, vibrators, corrosion inhibitors, air filters
C123S1980DB, C123S435000
Reexamination Certificate
active
06192854
ABSTRACT:
FIELD OF THE INVENTION
The invention is based on a fuel injection system for a multi-cylinder internal combustion engine.
In one such fuel injection system, known for instance from German Patent Disclosure DE 44 14 242 A1, each cylinder of the engine is assigned an injection unit, and each injection unit has one injection valve, one control valve, one flow limiting valve, and one injection nozzle. A fuel pump supplies these injection units with fuel via a fuel delivery line. The fuel injection system also has a control unit, which for injecting a predetermined fuel quantity into a combustion chamber of one of the cylinders of the engine electrically actuates the appropriate control valve for an injection duration that is correlated with the predetermined fuel quantity. By means of the actuated control valve, the injection valve, which is thus hydraulically coupled in the usual way, is actuated. In this way, the fuel delivery line upstream of the applicable injection nozzle is opened by the actuated injection valve, so that fuel is injected into the combustion chamber. The flow limiting valve is also disposed in the fuel delivery line upstream of the injection valve and blocks the fuel delivery line when the fuel quantity that has flowed through the flow limiting valve or is flowing out of the flow limiting valve attains a maximum fuel quantity. This maximum fuel quantity is predetermined and is the result of whatever fuel quantity is required to attain maximum engine power in all operating ranges of the engine without causing any damage to the engine, plus a tolerable leakage downstream of the flow limiting valve, for instance in the injection valve. The flow limiting valve is embodied such that once the flow limiting valve is closed, it does not open the fuel delivery line again until the fuel delivery line is blocked downstream of the flow limiting valve. This means that the flow limiting valve does not open again until the injection valve has properly closed, and no leakage is occurring in the fuel delivery line between the flow limiting valve and the injection valve. Such a flow limiting valve thus provides protection for the engine in the event of malfunctions of the injection units or leakage downstream of the flow limiting valve. For instance, the control valve and/or the injection valve might stick in an open position. The protective function of the flow limiting valve is due to the fact that the injected fuel quantity attains the aforementioned maximum fuel quantity, for instance if the injection valve cannot close because of a metal chip in the valve seat, and thus the flow limiting valve blocks the fuel delivery line. If the affected injection valve still cannot close, then the fuel delivery line remains open downstream of the flow limiting valve, so that the flow limiting valve no longer opens. Since the affected cylinder is then decoupled from the fuel delivery line, the affected cylinder cannot be damaged by a malfunction of the injection unit. The engine can still be operated in an emergency mode, however, so that without further provisions, the vehicle can for instance be driven to a repair facility.
In a corresponding way, a leak at the injection valve can cause the flow limiting valve to block the fuel delivery line; then the leakage at the injection valve prevents re-opening of the flow limiting valve. To allow the flow limiting valve to block the fuel delivery line in the event of a leak at the injection valve, however, the leakage quantity plus the injection quantity must attain the aforementioned maximum fuel quantity. Even a relatively small leak suffices in ranges of maximum engine power. In all the other operating states of the engine, in which the fuel injection quantity is smaller, the leak must be correspondingly greater to allow the cylinder affected by the leak to be disconnected from the fuel delivery line.
OBJECT AND SUMMARY OF THE INVENTION
The fuel injection system according to the invention has an advantage over the prior art that a cylinder affected by a leak downstream of the flow limiting valve can be disconnected from the fuel delivery line even in the event of relatively small leaks, regardless of the engine operating state. The fuel injection system of the invention thus improves the operating safety of the engine.
To allow the flow limiting valve to close off the fuel delivery to the affected cylinder even in the event of relatively small leaks, in the fuel injection system of the invention, each injection unit is assigned at least one sensor, with which the fuel delivery line to the applicable cylinder can be monitored for leakage. As soon as a leak is found in the fuel delivery line downstream of the flow limiting valve, the corresponding sensor sends a signal to the control unit by means of a suitable leakage signal. The control unit then increases the injection duration for the affected cylinder, in such a way that the resultant fuel quantity injected into the combustion chamber of the affected cylinder is greater than the maximum fuel quantity. As soon as the fuel quantity flowing through the flow limiting valve attains the maximum fuel quantity, the flow limiting valve reacts as intended and blocks the fuel delivery line, so that the corresponding cylinder is decoupled from the fuel delivery line. Since a leak downstream of the flow limiting valve has been indicated by the sensor, the fuel delivery line downstream of the flow limiting valve remains open because of the existing link even if the injection valve is closed, and so the flow limiting valve can no longer open the fuel delivery line. Since the injection duration controlled by the control unit can be selected independently of the engine operating state, a cylinder shutoff is possible in all operating states, even in the presence of relatively small leaks.
If for instance the injection valve does not close completely because of contamination, a leak develops, as a result fuel flows permanently into the combustion chamber. For igniting the fuel, an overly large fuel quantity is then available after the usual injection event, so that an excess cylinder pressure arises in the affected cylinder. Moreover, such a leak in the engine can cause noticeable noise, which is typically called knocking. As sensors for monitoring leakage in the fuel delivery line, a knocking sensor and a pressure sensor are especially suitable and are then assigned to the applicable cylinder.
To reduce the risk of damage to the engine from the lengthening of the injection duration, the increase in the injection duration is limited such that the injection duration resulting from the increase is at maximum three times as great as the injection duration required to attain maximum engine power. Since the injection duration required to attain maximum engine power is dependent on the rpm of the engine at the time, a limitation in the increase of the injection duration is expediently made as a function of the engine rpm. This is done by providing that the injection duration can be increased at maximum enough that the injection can occur only as long as it takes an engine crankshaft, which is engaged by the pistons moving in the cylinders, to rotate by less than 300°; that is, the injection duration attainable by the increase is at maximum 300° of crankshaft angle. The increase in the injection duration is preferably limited to 105° of crankshaft angle.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawings.
REFERENCES:
patent: 4539959 (1985-09-01), Williams
patent: 5190013 (1993-03-01), Dozier
patent: 5433182 (1995-07-01), Augustin
patent: 5577479 (1996-11-01), Popp
patent: 5816220 (1998-10-01), Stumpp et al.
patent: 5868111 (1999-02-01), Augustin
Greigg Edwin E.
Griegg Ronald E.
Moulis Thomas N.
Robert & Bosch GmbH
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