Internal-combustion engines – Charge forming device – With fuel pump
Reexamination Certificate
2000-01-07
2001-10-23
Rivell, John (Department: 3753)
Internal-combustion engines
Charge forming device
With fuel pump
C137S504000, C138S043000, C138S046000
Reexamination Certificate
active
06305356
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a common rail system having a regulated prefeed pump, which pumps a fuel flow from a fuel tank to a high-pressure pump, the fuel flow being split with the aid of a valve assembly into a lubricant flow and a high-pressure feed flow that is pumped, acted upon by high pressure, into a high-pressure reservoir, and the prefeed pump has a substantially linear characteristic feed curve with a certain slope.
To improve the efficiency of common rail systems, it is necessary to establish an equilibrium in the pressure reservoir (rail) between the inflowing and outflowing fuel flow. The attempt is made to do this by on-demand quantity regulation. One such common rail system is described for instance in German Patent Disclosure DE 197 39 653, which had not been published before the priority date of the present application. To keep the lubricant flow constant, a flow regulating valve is used.
The high-pressure pump is driven via the engine. Thus, the rpm of the high-pressure pump is dependent on the engine rpm. In experiments in the context of the present invention, it has been found that the known flow regulating valve, while it does have good regulating performance in the upper rpm range, it does not perform well in the lower rpm range.
OBJECT AND SUMMARY OF THE INVENTION
An object of the invention is to furnish a common rail system of the type described at the outset that has improved regulating performance, especially at low rpm.
This object is attained, in a common rail system having a regulated prefeed pump, which pumps a fuel flow from a fuel tank to a high-pressure pump. The fuel flow is split with the aid of a valve assembly into a lubricant flow and a high-pressure feed flow that is pumped, into a high-pressure reservoir, and acted upon by high pressure. The prefeed pump has a substantially linear characteristic feed curve with a certain slope, in that for the lubricant flow, the valve assembly includes a valve whose characteristic feed curve initially rises in a first portion with the rpm of the prefeed pump with the same slope as the characteristic feed curve of the prefeed pump. Then in a second portion has a substantially linear course with a lesser slope than the characteristic feed curve of the prefeed pump, and in a third portion finally drops again. In the first portion, practically all the fuel flow furnished by the prefeed pump is diverted as a lubricant flow. In the second portion, the high-pressure feed flow slowly increases. In the third portion, the lubricant flow drops to a minimum that still assures adequate lubrication. This considerably improves the feed quantity characteristic at low engine rpm.
One particular kind of embodiment of the invention is characterized in that the lubricant flow valve has a flow cross section that is variable between an opened and a closed valve position. That in the opened position, the flow cross section is so large that a sufficiently large lubricant flow can pass through and then decreases as a function of the pilot pressure as soon as the valve begins to close. By means of the flow cross section that is variable as a function of the pilot pressure furnished by the prefeed pump, the lubricant flow initially rises and then drops again.
Another particular type of embodiment of the invention is characterized in that the lubricant flow valve includes a valve body with a through bore, in which a valve piston prestressed by a spring is movable back and forth. This valve is especially simple in design and especially economical to make. As the piston stroke increases, the flow area decreases. The regulating performance of the lubricant flow valve can be varied by way of the magnitude of the spring constant.
Another particular kind of embodiment of the invention is characterized in that the piston takes the form of a hollow cylinder, which in the closed valve position contacts one end of a tang, in which a longitudinal bore is installed. The longitudinal bore is disposed concentric with the valve piston, and in the opened valve position is spaced apart from one end of the tang. A transverse bore is installed in the tang and communicates with the longitudinal bore and, in the opened valve position, communicates also with the interior of the valve piston. By the use of this lubricant flow valve, it is possible to dispense with the known flow regulating valve. In experiments with the lubricant flow valve according to the invention, a considerably improved regulating performance at low engine rpm has been demonstrated.
Another particular kind of embodiment of the invention is characterized in that the diameter of the longitudinal bore in the tang is smaller than the inside diameter of the valve piston. In the closed valve position, the longitudinal bore of the tang acts as a throttle.
Further advantages, characteristics and details of the invention will become apparent from the ensuing description, in which an exemplary embodiment of the invention is described in detail in conjunction with the drawing. The characteristics recited in the claims and mentioned in the description can each be essential to the invention individually or in an arbitrary combination.
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 drawing.
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patent: 3872884 (1975-03-01), Busdiecker et al.
patent: 4198948 (1980-04-01), Conrad et al.
patent: 4383552 (1983-05-01), Baker
patent: 5469883 (1995-11-01), Lee
patent: 5701872 (1997-12-01), Kaku et al.
patent: 6021761 (2000-02-01), Kellner et al.
Faix Erhard
Loesch Gerd
Greigg Edwin E.
Greigg Ronald E.
Rivell John
Robert & Bosch GmbH
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