Internal-combustion engines – Charge forming device – With fuel pump
Patent
1994-08-02
1995-10-31
Moulis, Thomas N.
Internal-combustion engines
Charge forming device
With fuel pump
F07M 4114
Patent
active
054620333
DESCRIPTION:
BRIEF SUMMARY
This invention relates no a fuel pumping apparatus for supplying fuel to a compression ignition engine and of the kind comprising a bore and a pumping plunger mounted in the bore, an outlet from the bore through which fuel can be displaced to an associated engine during inward movement of the plunger in the bore, cam means for imparting inward movement to the plunger, a drive shaft which is driven in synchronism with the engine and operable in conjunction with the cam means to impart inward movement to the plunger in timed relationship with the engine, fluid pressure operable means associated with the cam means for varying the commencement of inward movement of the plunger, means for varying the quantity of fuel supplied by the apparatus to the associated engine, the fluid pressure operable means comprising a timing piston contained within a timing cylinder, means coupling the timing piston to a part of the cam means, the timing piston being biased towards one end of the timing cylinder by resilient means, the fluid in said one end of the timing cylinder acting to oppose the movement of the timing piston when the plungers are moved inwardly by the cam lobes, and a further piston contained within a further cylinder one end of which is connected to said one end of the timing cylinder, and a pre-stressed spring urging the further piston towards said one end of the further cylinder, said further piston and said timing piston yielding to allow movement of the piston under the action of the cam reaction forces.
In a first example of such an apparatus the plunger or plungers is/are mounted in a transverse bore formed in a rotary distributor member which is mounted in a fixed body and which is coupled to the drive shaft so as to rotate therewith. The cam means comprises an annular cam ring which has cam lobes on its internal surface and these are engaged by followers associated with the plungers. The cam ring is angularly movable in the body or housing of the apparatus to vary the timing of fuel delivery and this is effected by a fluid pressure operable piston. The quantity of fuel supplied by the apparatus Is determined by a valve means operable to spill fuel at a high rate from the bore. The valve may be a servo operated valve controlled either mechanically or electrically. The bore is completely filled with fuel during the filling period of the apparatus.
In a second example of the apparatus the plunger or plungers is/are again mounted in a transverse bore formed in a distributor member but the amount of fuel which is supplied to the associated engine is controlled by restricting the amount of fuel which is supplied to the bore using for example, an adjustable throttle member. The pumping plunger or plungers in this form of apparatus deliver fuel to the associated engine throughout their full inward movement in particular, while the associated cam followers move over the crests of the cam lobes. An example of this form of apparatus is seen in U.S. Pat. No. 4,132,508.
In a third example of the apparatus the plunger as well as being axially movable in the bore by the action of the cam means, is also coupled to the drive shaft so as to rotate therewith. The plunger is therefore able to act as a distributor element to ensure that fuel is delivered to a plurality of outlets in turn. A portion of the plunger extends from the bore and is surrounded by a sleeve the axial portion of which can be varied to alter the position during inward movement of the plunger, at which fuel is spilled from the bore.
In U.S. Pat. No. 4,132,508 the further piston and the timing piston are movable throughout the whole of the period the pumping plunger is movable inwardly by the cam and the practical effect is that the fuel injection characteristic is modified throughout the full inward movement of the pumping plunger. The purpose of the arrangement is to avoid having to change the cam profile in order to change the injection characteristic.
It is recognised in the compression ignition engine art that there is a need to minimise the amoun
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Lucas Industries Public Limited Company
Moulis Thomas N.
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