Oil Engines and Transmission Problems
Page 41
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THE second of three lectures on "Oil Engine Traction" was read by Mr. Alan E, L. Choi-lton, C.B.E., M.P., M.I.Mech.E., at the Royal Society of Arts, London, on March 14th. The first was reported in our issue for last week.
Mr. Chorlton began his second paper by giving a brief review of the various types of oil engine that had been used for transport since the period before the war. He traced the progress that had been made in reducing weight per horse-power, which was, of course, realized to be of primary importance, particularly in building engines for road work, and stated that this could be done to the extent called for only by increasing the speed.
He gave descriptions illustrated by slides, of a large number of engines, arid an interesting table of figures obtained from a 3-hour test made in 1.922 under the supervision of the Sir Ministry of the first engine to exceed
• 1,000 r.p.m.
These are some of the figures in question:— Revolutions per minute .. 1,007 Brake horse.power ... 424 Brake mean effective pressure, lb, per eq. 92.5 Fuel, lb. per b.h.p.-bour0.365 Lubricating oil inlet and outlet temperature, degrees F.... 121.133 Imbricating oil pressure, lb. per sq. in. ... ... 47 Water to engine inlet and outlet temperature, degrees F. 140-150 Fuel-control range, degrees ... 22.5 Mean efficiency (mechanical), per cent, ... 86 This engine had six cylinders of 8 ins. by 12 ins., in line, and weighed only 8,0011 lb.
The results of these tests, incidentally, were so encouraging that a set of five slightly larger engines was constructed and formed the power plant of the airship 11101.
These engines, he said, were the forerunners of the lighter weight, faster-running type.
• He went on to discuss the smaller engines—also developments of the same prototype—which run at speeds up to 2,500 r.p.m. and are becoming more and more widely used for road transport.
Coming to the subject of transmission systems, he divided them into six classes :—(1) Hydraulic, infinitely variable ; (2) mechanical, with toothed gears and clutch controls; (3) compressed air, vapour or gas ; (4) electrical ; (5) direct; (6) mixed.
Although the actual systems discussed were mainly those used in rail work, they are by no means without interest to the road engineer.
Mr. Chorlton described three types of hydraulic transmission : the piston or plunger variety, the radial-vane rotary type, and the centrifugal or turbine pattern.
In the first class he dealt with the Williams-Janney, in which a variable-angle swash-plate operates the pump plungers, the stroke of which can be graduated from nothing to maximum. This, he remarked, seemed ideal, theoretically, and it was hard to explain whylt had not encountered greater success. It showed good efficiency and the heating up of the oil seemed a minor difficulty.
He quoted the Lentz as the best known example of the second class, and the Fottinger as the earliest and best known example of the third.
The Fluid Flywheel, he said, was a more simple form, and he forecast the day when it would have advanced so much as to take the place of the gearbox. He described several systems of compressed-air transmission. The loss doe to compression and re-expansion, he said, was overcome by employing the exhaust gases to reheat the air before use in the power cylinders. But the efficiency of this method was dependent upon the load on the engine.
He dwelt at length upon electric transmission as employed on the rail, and remarked on the disappointingly slow progress it had made on the road.