Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1991-09-06
1992-09-15
Miller, Carl S.
Internal-combustion engines
Charge forming device
Fuel injection system
123300, F02M 4502
Patent
active
051468948
DESCRIPTION:
BRIEF SUMMARY
The invention is based on a reservoir-type fuel injection system as defined hereinafter.
In reservoir-type fuel injection systems of this kind, fuel is placed in a pressure reservoir under pressure by a charge pump that pumps continuously; a check valve is provided between the charge pump and the pressure reservoir to prevent fuel from being forced back into the pump under pressure in the intake stroke of the pump. Consequently, reservoir-type fuel injection systems require control devices that monitor the quantity and timing of the further supply of the fuel under pressure to the injection nozzle; rotating distributor shafts and/or valve assemblies, particularly magnet valves are used for this purpose, for example. In typical reservoir-type fuel injection systems of the type referred to the outset above, there is no separate regulation of the charge pump, and provision is made merely that the charge pump pump an adequate quantity of fuel to the reservoir, which makes it impossible to completely evacuate the reservoir, particularly at high rpm.
In reservoir-type fuel injection systems, injection can be done directly into the engine combustion chamber during both the intake stroke and the compression stroke of an Otto engine. To improve emissions, it has become known to divide the injection quantity into portions, in particular a pre-injection quantity and a main injection quantity. Particularly in multi-cylinder engines, this can result in an overlap in drawing fuel from such a reservoir, and overlapping of pre-injection and main injection events in various cylinders can occur. Such overlapping of injection events can consequently lead to problems in exact metering of the injection quantities, and it is not readily possible to insure defined injection quantities for various injection events.
From Japanese Patent Document A 57/212362, a reservoir-type fuel injection system is known. In the known system, however, the two reservoirs, one of which serves to store the fuel injection quantity for the pre-injection and the other to store the fuel injection quantity for a main injection, communicate parallel to one another with the pump work chamber of the high-pressure pump, each via an interposed check valve. This arrangement has the disadvantage that upon filling of the reservoir, the quantity of fuel pumped per pump piston stroke by the high-pressure pump, which is embodied as a piston pump, is divided into the two reservoirs, but there is no assurance as to which quantity of fuel pumped by the high-pressure pump reaches which reservoir. Filling of the various reservoirs depends on various parameters, such as the flow resistance, the opening pressure of the check valves, and the reservoir spring. The result, especially if, as is typical, the pre-injection quantity is kept very small, is a relatively major error in the pre-injection metering quantity.
The embodiment of the reservoir-type fuel injection system according to the invention, contrarily, has the advantage that by the stroke limitation of the movable wall such as a piston of the first reservoir, a defined fuel quantity can be pre-stored, and can in particular advantageously be used for a pre-injection. For this kind of injection, the reservoir piston is always located in a defined outset position before the metering of the applicable fuel injection quantity from this reservoir is controlled. The stroke limitation assures that the following reservoir will be reliably filled, and its movable wall will be moved up to a position defined by opening the overflow opening. At the instant of metering a defined outset position of the movable wall thus exists, which increases the accuracy of injection and fuel metering.
The embodiment of the reservoir-type fuel injection system according to the invention further has the advantage that overlapping of injection events, particularly when the injection event is divided into a pre-injection and a main injection event, can be avoided, and that it can simultaneously be assured that for both the pre-injection and the ma
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Linder Ernst
Rembold Helmut
Greigg Edwin E.
Greigg Ronald E.
Miller Carl S.
Robert & Bosch GmbH
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