Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1997-04-30
2001-05-15
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S456000, C138S113000
Reexamination Certificate
active
06230684
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based on and claims priority of Japanese Patent Application No. Hei. 8-123850 filed on May 20, 1996, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fuel supply apparatus for a direct injection type gasoline engine, for injecting high-pressure fuel directly into each cylindrical combustion chamber of the engine.
2. Description of Related Art
Recently, to improve economical fuel consumption and engine output power, a direct injection type gasoline engine has been developed in which fuel is injected directly into each cylindrical combustion chamber. In such a direct injection type gasoline engine, to facilitate atomization of fuel (gasoline) to be injected directly into each combustion chamber, the pressure of fuel supplied to fuel injection valves (fuel pressure) is increased to be high. Preferably, the fuel pressure should be increased to a high level promptly. Further, when fuel pressure varies during operation of the engine, the amount of injected fuel varies, and emission or driveability deteriorates. Therefore, it is preferable that fuel pressure should be maintained at a substantially constant value by suppressing variation in fuel pressure during the engine operation.
To secure increase of fuel pressure at starting and to suppress sequential fuel pressure variation, as shown in JP-U-5-1854, an accumulator is connected to a common rail (delivery pipe) for the fuel injection valve of each cylinder. A control valve and a high-pressure regulator for regulating fuel pressure is connected to the common rail, so that variation in fuel pressure during engine operation is suppressed by the high-pressure regulator. Further, during engine operation, the control valve is opened to introduce a part of the high-pressure fuel into the accumulator. At stopping of the engine, the control valve is closed to seal up high-pressure fuel in the accumulator. Subsequently at starting of the engine, the control valve is opened to introduce high-pressure fuel already in the accumulator into the common rail so that the rail fuel pressure is increased promptly at engine starting to improve starting performance.
However, in the above-described fuel supply apparatus, since the control valve, accumulator, and high-pressure regulator are necessary to secure improved starting performance while also suppressing sequential fuel pressure variation, the construction of the fuel supply system is complicated and contrary to desired requirements of small-sized apparatus and low cost.
SUMMARY OF THE INVENTION
In view of the above-described problems, an object of the present invention is therefore to provide a fuel supply apparatus for a direct fuel injection type gasoline engine which has a simplified construction to reduce its cost and size.
According to the present invention, a fuel supply apparatus for a direct injection type gasoline engine includes a damper, in which gas is sealed, stretching and shrinking in a direction to suppress variation in fuel pressure in a common rail. A pressure at which gas is initially sealed within said damper is set to be greater than a predetermined pressure required for atomizing fuel.
To reduce variation in the common rail fuel pressure , it is advantageous to increase the volume of the common rail; however, when the common rail volume is increased, an increase in common rail fuel pressure at engine starting is delayed and starting performance deteriorates.
According to the present invention, when the common rail fuel pressure lowers at engine stops, the damper is displaced in a direction to suppress an increase in fuel pressure, i.e., in a direction as to reduce the volume in which fuel is sealed. Therefore, the state at engine starting is substantially the same as where the common rail volume is reduced, and the desired increase in fuel pressure at engine starting is accelerated. Further, since variation in fuel pressure can be suppressed by stretching and shrinking of the damper, the common rail volume can be reduced. In addition, since the pressure at which gas is initially sealed within the damper is set to be greater than a predetermined pressure required for atomizing fuel injected from the injection valve, at starting, the damper does not move until the fuel pressure reaches a predetermined value. Thus the volume in which the fuel is sealed is maintained at a minimum. In this way, it is possible to increase fuel pressure at starting promptly to be greater than a predetermined value required for atomizing fuel injected from the injection valve. Accordingly, favorable combustion can be secured early, and favorable starting performance can be secured. Further, during engine operation, the damper shrinks until the pressure of the gas sealed in the damper is balanced with the fuel pressure. In this state, the damper stretches according to variation in fuel pressure so that variation in fuel pressure can be suppressed.
Thus, according to the present invention, by using a gas-sealed type damper, both of the desired performances (increasing fuel pressure at starting and subsequent suppression of variation in fuel pressure) can be secured. Therefore, as compared with the situation where the control valve, accumulator and high-pressure regulator are assembled, construction is simplified, and cost and size can be reduced.
The pressure at which gas is initially sealed within the damper may preferably be set for 4 MPa or more, more preferably, for 8 MPa or more.
Further, the pressure at which the gas is initially sealed within the damper may be set to be lower than normal operation fuel pressure within the common rail, more preferably, lower than normal operation fuel pressure within the common rail by 1 MPa or more.
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Furuhashi Tsutomu
Hioki Tomomi
Inoue Hiroshi
Denso Corporation
Miller Carl S.
Nixon & Vanderhye PC
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