Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
2000-07-27
2001-12-25
Solis, Erick (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S499000, C361S154000
Reexamination Certificate
active
06332454
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese Patent Application No. 11-224029 filed on Aug. 6, 1999.
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for driving an electromagnetic valve used for supplying fuel to an engine of a vehicle.
A conventional electromagnetic valve driving apparatus of this type is disclosed in U.S. Pat. No. 4,605,983 (JP-B2-4-42805). When this apparatus is applied to a high-pressure fuel pump, a conduction current flowing through a coil employed in an electromagnetic valve is driven to reach a predetermined magnitude Ip before a predetermined period of time lapses after the start of the valve driving so that the movable body of the valve may be actuated quickly. Thereafter, the conduction current is reduced to a small holding magnitude Ih (<Ip) which is large enough only for holding the movable body of the valve at the current position. As a result, a good driving response of the electromagnetic valve or the operating response of the valve body can be attained by merely supplying a reduced conduction current or a reduced driving current.
In a state where the engine is being started or various electric loads are turned on under a low engine speed condition such as an idling, a battery voltage drops due to the operation of a starter motor or the electric loads. In addition, the conduction-holding period becomes longer at a very low engine speed. It is therefore likely that the battery voltage substantially decreases even during the conduction-holding period. As a result, according to the above apparatus, the amount of fuel supplied to the engine during the start time of the engine is not sufficient and the start characteristic of the engine is lessened.
U.S. Pat. No. 4,605,983 also discloses to lengthen a predetermined period of limiting the conduction current to a peak current as the voltage of the battery decreases. However, this is not useful for solving the problem of a drop in battery voltage, which occurs in the conduction-holding period following the predetermined period.
The above problem occurs irrespective of the type of the electromagnetic valve, that is, a normally closed-type or a normally open-type. In addition, the above problem is also encountered in the case of an electromagnetic valve employed as a fuel injector (a fuel injection valve) for supplying fuel to the engine. In this case, if the duration of the operating time of the electromagnetic valve becomes too short, the amount of fuel supplied to the engine is not sufficient by a quantity determined by a decrease in operating-time duration.
In another conventional apparatus disclosed in JP-A-8-4576, a current supplied to a fuel injection valve is set at a value higher than that of the ordinary operation only at the first injection at the time the engine is started. However, since it is still impossible to improve the start characteristic of the engine accompanying a drop in battery voltage, because the voltage drop is not predictable. In addition, in order to supply a current with a magnitude greater than that of a normal condition through the coil at a low battery voltage, a voltage raising circuit must be provided.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide an electromagnetic valve driving apparatus capable of ensuring a good valve driving characteristic for an engine.
According to the present invention, a driving apparatus for an electromagnetic valve which supplies fuel to an engine comprises a conduction control circuit and a current-limit-value setting circuit. The conduction control circuit turns on and off a switching device so that a conduction current flowing through a coil of the electromagnetic valve has a magnitude equal to a predetermined current limit value. The predetermined current limit value used in the conduction control circuit is initially set to a first current limit value, which is high enough to move a valve body, during a predetermined period. When the predetermined period has lapsed, the predetermined current limit value is switched from the first current limit value to a second current limit value, which is smaller than the first current limit value thereby to maintain a position of the movable body. In addition, when the microcomputer detects a start state of the engine or a low level state of a battery voltage, the second current limit value is raised to a third current limit value higher than the second current limit value so that the movable body may be driven with the higher current to thereby shorten a period in which the electromagnetic valve becomes inoperative.
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patent: 4680667 (1987-07-01), Petrie
patent: 5937828 (1999-08-01), Watanabe
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patent: 6283095 (2001-09-01), Krueger
patent: 8 4576 (1996-01-01), None
Itabashi Toru
Yamada Atsushi
Denso Corporation
Nixon & Vanderhye PC
Solis Erick
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