1996-07-02
1997-07-29
Moulis, Thomas N.
F02M 3704
Patent
active
056513488
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a fuel pumping apparatus for supplying fuel to an internal combustion engine and comprising a high pressure pump including a reciprocable pump element, a cam mechanism operable to actuate the pump element in timed relationship with the associated engine and a fluid pressure operable piston coupled to the cam mechanism, the piston being mounted in a cylinder and acting to vary the timing of fuel delivery to the associated engine in accordance with the pressure of fluid in one end of the cylinder.
In one form of such an apparatus the pump element is in the form of a pair of pumping plungers mounted in a radial bore formed in a rotary part of the pump. The rotary part is driven in timed relationship with the associated engine and at their outer ends the plungers engage cam followers respectively which in turn can engage cam lobes formed on the internal peripheral surface of a cam ring which is mounted for angular adjustment about the axis of rotation of said part. The piston and the cylinder are tangentially disposed relative to the cam ring and are mounted in a body part of the apparatus with the piston defining a recess intermediate its ends and into which extends a peg extending radially from and mounted on the cam ring. The piston is spring loaded in the direction of rotation of the aforesaid part so as to move the piston and cam ring in the timing retard direction and is movable in the opposite direction against the action of the spring, by fluid under pressure which is admitted into the cylinder.
During the operation of the pump the cam ring is subjected to reaction forces particularly when the cam followers engage the leading flanks of the cam lobes. This reaction force is resisted by the creation of an hydraulic lock in the cylinder. The apparatus is required to function over a wide temperature range and it has been the practice to provide an anodised aluminium piston in a bore formed in an aluminium body. This overcomes the problem of differential expansion so that the working clearance between the piston and the wall of the bore forming the cylinder, remains more or less constant over the temperature range. With such an arrangement the piston has to be provided with a steel or like insert for engagement by the peg in order to ensure an adequate surface life. If a steel piston is utilised in the bore so as to overcome the need for the special insert, the working clearance varies with temperature and since the components have to be machined to provide the correct working clearance at the lowest temperature of the temperature range, the working clearance increases as the temperature increases. This leads to increased leakage of liquid along the working clearance so that the hydraulic lock becomes less effective, and it also allows the piston to tilt in the bore under the action of the hydraulic and mechanical loading.
The object of the present invention is to provide an apparatus in an improved form.
According to the invention in an apparatus of the kind specified the piston at said one end of the cylinder defines a blind recess in which is slidably mounted a spigot extending inwardly from an end closure of the cylinder, said spigot and the piston being formed from materials having the same or similar coefficients of expansion, the spigot and the recess defining a working chamber, valve means through which fluid can flow into said working chamber from said one end of the cylinder when the piston is moved away therefrom and restricted passage means through which fluid can flow out of said working chamber as the piston moves towards said one end of the cylinder.
An example of a fuel pumping apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which:
FIG. 1 shows a part sectioned section through a part of a pumping apparatus incorporating the invention, and
FIG. 2 shows to a smaller scale a sectional side elevation of the remaining part of the apparatus.
Referring to the drawings the apparatus includes a body 10 which is
REFERENCES:
patent: 4143632 (1979-03-01), Kobayashi
patent: 4593669 (1986-06-01), Igarashi
patent: 4753211 (1988-06-01), Hofer
Lucas Industries Public Limited Company
Moulis Thomas N.
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