Fluid pump

Abstract

A pump for fluid, comprising a pump body defining a bore, a pumping plunger having an end region which is slidably received within the bore, a spill port defined by the pump body in a wall of the bore which port is coverable by the end region of the pumping plunger as the plunger is driven on a pumping stroke, in use, so as to initiate fluid pressurization within a pumping chamber; and a spill feature defined by the pumping plunger being arranged to uncover the spill port during a pumping stroke so as to cause depressurization of the pumping chamber. The pumping plunger further defines a speed sensitive feature configured to permit a controlled leak of fluid from the pumping chamber to the spill port towards the end of a pumping stoke. The invention also encompasses a pumping plunger particularly suited for use in the above described pump.

Description

TECHNICAL FIELD[0001]The present invention relates to a fluid pump. More specifically the invention relates to a ‘unit pump’ type fuel injection pump for use in a compression ignition internal combustion engine in which a pumping plunger reciprocates within a plunger bore in order to pressurize fuel within a pumping chamber. In addition, the invention relates to a pumping plunger for use within such a pump.BACKGROUND ART[0002]FIG. 1 shows a sectional view of a known fuel injection pump, indicated generally as 2, which is suitable for use as a means of supplying pressurized fuel to a fuel injector of an internal combustion engine. Such a pump is generally known in the art as a mechanical ‘unit pump’. The fuel pump 2 includes a generally tubular pump housing 4 having an axially disposed bore 6 within which a pumping plunger 8 is slidable. The plunger 8 has a lower end 10 (in the orientation shown in FIG. 1) that is coupled to a lower spring plate 12. Although not shown in FIG. 1, in p...

AI Technical Summary

Benefits of technology

[0015]The speed sensitive feature is adapted preferably to be effective during a rated load operating condition of the pump and has the effect of reducing the delivery of the pump at lower pump speeds compared to a pump having plungers without the speed sensitive feature. However, at higher pump speeds delivery remains substantially unaffected. The invention has particular utility in internal combustion engines in which it is important to minimize exhaust emissions, for example small capacity road vehicles. Moreover, the speed sensitive feature is configured to be effective towards the end of a pumping stroke which enables the relationship between fuel delivery and injection timing for high speed operation to be preserved. Although the speed sensitive feature may be effective over a broad range of angular movement of the plunger, it is preferred that it is effective during approximately the last 20 percent of the range of angular movement of the plunger which corresponds approximately to the rated load operating condition of the pump.

Problems solved by technology

However, at higher pump speeds delivery remains substantially unaffected.

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