A POSITIVE FEED CARBURETTER.
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THE principal problem in connection with the design of an efficient car. huretter is that of circumventing the natural tendency of "the component to supply mixture of a quality which varies with the throttle opening, the variation, unfortunately, not being in accordance -with the real requirements of the engine. If ii. petrol engine were always to run at one pre-determined speed, this problem would not arise, as it is a comparatively easy matter to arrange for the correct mixture to be supplied at a given engine speed. So soon as variations in that. speed have to be catered for, then so soon does it become necessary to provide additional jets pilot jets, compensating jets, and all the other gadgets so dear to the carburetter expert. The cause of all this trouble is the difference between air and petrol, in respect of their inertia, the effect of which it to cause the air to pick up more and more petrol as its speed past the jet increases. It follevis that, at low speed, a carburetter set to give the correct mixture at slow speeds would feed too rich a gas at high speeds, and, conversely, one which was designed to provide correctly proportioned gases at high speeds Would supply a mixture which would be too poor for slow running.
In some quarters the view is held that success is only to be achieved along lines quite different from those to which the ordinary user of carburetters is accustomed. Instead of trying to improve matters by using a multiplicity of jets, the principle of a positive feed is employed, so that measured amounts of fuel are positively pumped into the induction pipe or mixing chamber, the amount of fuel varying strictly in accordance with the revolutions of the engine, with provision for adjustment or slight modification of that condition. A carburetter of the latter type has been patented recently .by a Mr. C. J. Erade, of 213, South Oroxted Road, West Dulwich, and the design embodies an important feature in connection with the pump which delivers the fuel to the jet or jets. Its construction is clearl7 shown by the' accompanying illustration. The customary &Lid, chamber is used to maintain a supply of petrol at a convenient level. The body of the pump is cast in one with the float chamber, its barrel being the small bore hole immediately below the pump plunger, winch can be seen to the right of the chamber. The plunger is shown, in the drawing, near to the upper limit of its stroke. Two important points should be noted. In the first place, the pump is submerged, so that petrol can readily enter the barrel under the influence of gravity, and any relief of pressure on the upward Stroke does not cause the space below the piston to be partly -filled with
vapour. In the second, it will be remarked that the plunger, in the upper position, stands quite_ clear from the barrel of the puinp. The effect of these two features is to eliminate the need for any valves, except the non-return valve shown.
The plunger is depressed by an enginedriven rocking lever, operating on the top of the plunger : it is returned by a spring. The stroke of the plunger, in regard Jo the depth to which it. enters the barrel of the pump, i is regulated, in the example shown n the drawing, by mounting the rocking lever on an eccentric centre. Partial rotation of the eccentric effects the position of -the rocking lever for any position of the driving rod, and thus controls the motion of the plunger. The movement of the eccentric would be under the immediate control of the driver ; it might very well be linked up to the throttle control lever. Supplementary adjustments of the relative positions of the end of the plunger and the business end of the rocking lever is afforded by means of the set-screw shown. Other methods of varying the actual amount of fuel delivered per stroke of the engine are indicated in the specification (134,356), and are covered by the patents.
The advantages claimed are More efficient control of the fuel supplied to the engine, simplicity of design, resulting in economy of manufacture, and the automatic variation of the fuel supply in accordance with the volume of the gaseous mixture