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Departure in Injection-Pump Design

9th July 1954, Page 61
9th July 1954
Page 61
Page 61, 9th July 1954 — Departure in Injection-Pump Design
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FOR some considerable time past Mono-Cam, Ltd., 28 Queen Anne's Gate, Westminster, London, S.W,1, have had in course of development 1. fuel-injection pump in which the elements are disposed radially as apposed to the conventional in-line trrangement. A number of these pumps

as been in experimental service troughout the country and so satisictory have been the reports that the nit is now to be put into production. With the present trend towards the ie of oil engines in the lighter types goods vehicle chassis, the need for ving closer study to the price fferential as between the oil engine id the petrol unit becomes of great iportance. One of the most expensive tgle items of equipment is the injecm pump, a precision component iich does not lend itself to cheap, lifferent mass-production techniques. Price, of course, must be governed 3t, by the extent of the demand and mndly, by the design as it may luence flow-production methods. • In the Mono-Cam pump the barrel and plunger assemblies are disposed radially to the axis of the camshaft. The face cam, which forms an integral part of the shaft, operates the plungers through a form of barrel tappet gear provided with wide-faced rollers which bear on the cam face. The camshaft being short, of generous diameter and well supported against the working load, it should prove particularly free from torsional vibration and bending deflections.

An unusual feature of the plunger design is that there is no helix, its place being taken by a parallel groove. It is well known that much of the wear to which plungers are subjected is due to the considerable side thrust exerted on them. By dispensing with the helix, such forces are balanced and therefore wear is considerably reduced, Injection is controlled by a sleeve which surrounds the plunger. Injection begins when the plunger moves up the barrel and uncovers the port holes therein; injection ceases when the outward motion of the plunger finally causes the parallel groove in the plunger to leave its surrounding sleeve.

It is claimed that the cut-off with this type of element is particularly sudden as the whole circumference of the plunger groove is uncovered simultaneously. Dribble at the injector is thus reduced and carbon formation at the injector is less prevalent.

Both the governor and fuel-lift pump are built as a unit with the injection pump and yet the type B component for six-cylindered engines measures only 101 in. by 4/ in. and weighs 171 lb.

Two forms of governing are available, either fully hydraulic or pneumatic-hydraulic. In the former case the pressure created by the " spill " of the pumping elements is utilized for governing over the whole speed range, and in the latter case a combination of the " spill" pressure and intake manifold depression is utilized. With pneumatic-hydraulic governing close control is given over idling and overspeeds.

The fuel-lift pump is extremely simple, the power source being the main face cam. This operates a plunger through a roller and lever, the latter being suitably arranged to be moved by an external control for priming purposes.

Pilot Injection Indicator diagrams show that pilot injection takes place at 400 r.p.m., and whilst this is not maintained over the whole range, a general characteristic of a slow initial rate followed by a steady main change ending with a sharp cutoff without after-injection, is noticeable over the whole speed and load range, A representative of The Commercial Motor has witnessed bench tests and has taken test runs in vehicles fitted with a Mono-Cam pump, and in all cases the performance has been of a standard commensurate with the claims made.

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