To Improve Oil-engine Slow Running
Page 33
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A New C.A.V. Device to Give Eight-stroking When Idling so that the Need for Extremely Small Fuel Deliveries is Obviated
PRECISE metering of small quantities of fuel is a function of every injection pump. Under 'all conditions of running, the quantities delivered by the respective pump elements need to be as nearly equal as is practically possible, but when delivery is cut down to the minimum for engine idling, the uniformity of the charges to each combustion chamber becomes of even greater importance, whilst the difficulty of accomplishing precise metering is proportionally increased.
With the object of removing the need for the delivery of very small .amounts of fuel, 'yet of obtaining regular and controlled slow running at no load, C.A.V., Ltd., Acton, London, W.3, has evolved a scheme for cutting-out altogether alternate deliveries from each element. By this means the minimum quantity injected can be roughly doubled, whilst the difficulties of design and construction are proportionally reduced.
The scheme is to shut off the feed to the pump inlet ports, this being done by rotary valves running at half camshaft speed. Our illustrations, which are based upon those contained in the recently published patent specification describing the device (No. 547,370), relate to a fourcylindered unit. It will be observed that the four rotary valves are mounted on a sliding shaft.
When this is in its position for normal running, a continuous groove on each valve is in alignment with its respective port. If the shaft be moved axially the continuous grooves are shifted out of register With the ports. At the side of each groove, however, a slot, subtending an angle of rather less than 180 degrees, is formed. The slots are appropriately spaced apart in a radial sense, so that the inlet ports are uncovered as the valves rotate, in a suitable sequence. This results in the engine eight-stroking. A means for automatically bringing the scheme into operation is depicted in the side-elevation drawing. When the rack rod (seen below the rotary valves) approaches the position for minimum delivery, a pressure-oil valve, on the end of the control rod above the rotary valve, is opened and oil is admitted to a cylinder at the right-hand end of the rotary-valve shaft and shifts it to the left.
When eight-stroking, the engine requires, as was pointed out earlier, a larger charge; accordingly the rack rod is required to take up a new position so soon as the rotary valves have shifted, and to effect this its, setting is automatically adjusted by a link operated by the left-band end of the rotary-valve shaft.
It will be noted that a fitment on the end of this shaft transmits axial motion of the latter to the link. A further function of this part is to serve as a fulcrum for the link during normal running when motion has to be transmitted from the upper rod to the rack rod below.