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A NEW DESIGN OF SWASH-PLATE ENGINE.

23rd October 1923
Page 10
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Page 10, 23rd October 1923 — A NEW DESIGN OF SWASH-PLATE ENGINE.
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The Eight-cylindered Horizontal Michell Engine with Four Pairs of Pistons Operating on a Swash-plate.

ENGINES in which a swash-plate or inclined disc. is used te replace a crank and in which the cylinders have been arranged parallel with and around the mainshalt are by no means new. certain difficulties seem, in most cases, to have prevented the type from becoming popular, and we go so far as to say that, had this engine emanated from any ordinary source, we should have ,looked upon it. as a mere variation of the dcsigns which have gone before, and which have shown se little promise. The Michell engine is the outcome of the brain of Mr. A. G. M. Michell, whose inventioni of a thrust bearing for marine propeller shafts has effected such a great saving in fuel for the propulsion a ships. Coming from such a source we rfeel that we may, at last, expect something really good in the way of a awashplate engine.

As regards the engine itself, there is little which diKers from those designs which have been seen before. The chief point of novelty consists of the introduction of the Michell bearing principle in association with the awash-plate of such an engine. Before describing the • swish-plate and its appurtenances, it is necessary that the principle of the Michell bearing should be thoroughly grasped. This bearing ha ti proved such an object-lesson in lubrication '-to eu-• gineers that we feel sure that a. clear understanding of its principle will be interesting to-all those who are connected in. any way with mechanisms which require lubrication. The Michell principle has shown us beyond all doubt that two surfaces forming a bearing can he absolutely kept from contact with each other by a lubricant, provided that the lubricant is introduced in a certain •manner. The Michell bearing was first applied to the thrust ef a marine propeller shaft, where the whole energy of the engine is converted into a thrust load which pushes the ship through the water.

In the ordinary way, one thrust bearing alone' was unable to maintain its lubrication between the surfaces owing to the -encinnotis pressure ;per square ineh :ot -available area. Toovercome this difficulty, a number of thrust bearing.s were arranged along the Shaft to act simultaneously; The Michell invention, however, enabled a single thrust bearing to do the work previously distributed over a number. The idea is that of introducing the oil between the surfaces in the form of a tapered film. Fig. 1 shows a block of metal moving along a metal surface in the direction of the arrow. Lubrication is shown as being present an the lower surface, but it is being scraped' off instead of passing between the two surfaces. This is due to the fact that the pressure is applied to the upper block at the point marked A, which is midway along the block. Fig. 2 shows the same block, but with the pressure applied as in the Michell plan at B, whih is two-thirds the .-length of the block from the front and one-third from the rear end. This method of supporting the block causes a slight tendency for the front end to cock ,up and to allow a tapered film of oil to enter between the surfaces as shown. Fig. 3 shows a marine thrust bearing, and Fig. 4 shows a journal hearing designed for marine use. It will be seen that in both of the applications of the principle the actual bearing surface is cut up into separate pads„ each pivoted as in Fig. 2. These bearings will only function properly so long as the rotation is in the one direction. The invention may seem to turn

on a very small thing, yet that small thing has already saved the country millions of tons of fuel. That the tapered film theory is supported by practice there can be no doubt, as we have recently seen a thrust bearing working with no lubricant other than air, when that air had been induced to enter between the surfaces in exactly the manner described above. That the air did actually separate the surfaces was proved by the fact that, in a demonstration model devised for the purpose, an electric contact was broken as soon as the bearing began to revolve. Having now made the principal feature of difference between this engine and its predecessors clear, we will desoribe the general con.struction. The engine has eight cylinders, all lying parallel. to the mainShaft, as shown in Figs. 5 and 6. The pistons are in pairs, and are connected by Means of a sleeve, which is provided with a gap in which the swath-plate can work. Each pair of cylinders is provided with two pads which make contact with the sides of the swaah-plate. These pads have a half-spherical face, where they bear against the sleeve of the pistons. The Michell plan is carried out in these pads, as the spherical bearing is not central, but is to the rear of the pad so as to allow the tapered film of oil to form between the pad and the swathplate. The position of these spherical bearings is shown in the end view (Fig. 6). Fig. 7 shows diagrammatically the , way in which the pistons span the edge of the swath-plate. An important feature in the design of the swash-plate is that its thickness, when measured axially, is always constant, as shown in Fig. 8. An adjustment for wear is provided behind the sphenioal bearing el the pad, as shown in Fig. 5. As the remainder of the design shows no departure from standard practice, we do not think it necessary to go farther into details than we have, but hope shortly to be able to deal more fully with the engine and its tests.


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