Engineering

Progress, Volume VIII, Issue 2, 1 October 1912, Page 91

Engineering

By Chas. C. Allen, Wh.Ex., A.M.1.M.E., Auckland

THE BROOKFIELD SILENT ENGINE

The adoption of the Daimler Motor Co. of the Silent Knight engine marked a new era in the history of motor car engineering. For years the leading motor car manufacturers had spared neither time nor expense in attempting to make cars more silent, apparently without realising that much of the noise was due to the impact of the cam and spring actuated valves. The possibilities of the silent engine

were, however, fully appreciated by the Daimler Company who, after careful experimental investigation, did not hesitate to discard, in the case of their most up-to-date cars, the elaborate and expensive tools they had made to facilitate the interchangable manufacture of an engine thoroughly efficient and satisfactory except as regards silence. The Silent Knight car, when put upon the market, was a revelation to the motoring world. Up to the present, however, very little seems to

have been done in connection with silent engines for marine purposes. Messrs. Brookfield Bros., of St. ._ Better's Bay, Auckland, are, after exhaustive tests, putting upon the market a silent engine specially designed for launch work. They have just completed a 30 h.p. launch engine, and are now engaged upon the adaption of their design to motor car work. The following advantages are claimed for the new Engine:—l. Perfect silence of all working parts. 2. Economy in fuel. 3. Durability. 4. Reliability. 5. Total absence of springs. 6. More

powerful (taking like dimensions). 7. Flexibility. 8. Perfectly steady running. The design is totally different from that of the Silent Knight engine. In the latter the valves are replaced by a reciprocating cylindrical sleeve encircling the cylinder. In place of this Messrs. Brookfield Bros, employ a balanced revolving valve placed on top of the Cylinder and driven from the crankshaft by means of two pairs of helical gears and a vertical shaft. The explosive gases are ad-

mitted at one end of the sleeve and the products of combustion are exhausted at the other.

The manner in which the explosive, and exhaust gases are controlled is shown by the accompanying diagrams. The sectional views represent vertical sections through the centre of the cylinder. Separate pairs of ports are employed for admission and exhaust, the large port area provided allowing the gases to pass to and from the cylinder very freely. Fig. 7 illustrates the arrangement of the ports. • Figs. 1 and 5 illustrate the admission stroke. . The downward movement of the piston tends to cause a partial vacuum in the cylinder, and the explosive gases enter through the admission ports which simultaneously open and close at the beginning and end of the stroke respectively. Fig. 2 illustrates the compression stroke. The upward movement of the piston compresses the explosive charge. As the ports in the valve casing are exactly opposite each other and equal in area the pressures on the two sides of the revolving sleeve balance and, there is no tendency to cause any frictional resistance to the rotation of the sleeve during this stroke. Fig. 3 illustrates the firing stroke. Upon the explosion of the compressed charge by the electric spark the piston is forced downwards. The pressures on the two sides of the revolving sleeve balance each other and no frictional resistance is caused. Pigs. 4 and 6 illustrate the exhaust stroke. As the two ports open simultaneously the exhaust gases commence to leave the cylinder and the upward stroke of the piston completes the discharge. The sleeve casing is water jacketed in the same way as the engine cylinder. This prevents overheating and makes the efficient lubrication of the sleeve a simple matter. The passages in the sleeve casing are traversed by both the explosive and exhaust gases. The latter during their journey heat up the metal to a certain extent. The explosive gases, which follow immediately, absorb a portion of this heat and become completely vaporised, a considerable cooling effect being produced. Owing to the complete vaporisation of the charge the firing stroke is more powerful than in the case of the ordinary type of engine, and fuel is saved. The ordinary tappet valves are subject to many disadvantages, such as pitting, wear, broken stems, broken springs, etc. In many cases engines are kept at work as long as they will run, although much power may be lost and fuel wasted owing to valve defects. In the revolving sleeve engine such disadvantages are altogether absent. The sleeve is simply made a working fit in the casing, both cylindrical surfaces being ground, the only clearance provided being that sufficient to admit the film of lubricant. As the sleeve is perfectly balanced at all times there is practically no friction, and, therefore, practically no wear. Valve troubles are quite eliminated. In the ordinary type of engine a considerable

amount of power is absorbed in driving the valves which are held in position by springs. When opening the exhaust valve the pressure on the valve head has to be overcome, in addition to the spring resistance, In the Brookfield engine there is no such waste of power developed in the cylinder, as the balanced sleeve revolves quite easily at all times. Before the revolving sleeve was adopted most extensive tests were made as to reliability. In one case the engine was run continuously for several hours without oiling the sleeve and without allowing the circulating water to pass around the sleeve casing. The experimental engine has been running continuously at full load from six to twelve hours a day for the past 15 months, and the sleeve is as good as when first put to work.