GUILLOTINE VALVES

Evening Star, Issue 22722, 9 August 1937, Page 15

GUILLOTINE VALVES

A HOVEL DESIGN Despite technical competition from sleeves. rotary, valves, ,apd other mechanises, the proper. Y?'yo is still almost universally employed l° r v 1( - engines of motor cars, commercial vehicles, and aircraft. It has now to face the advent of another rival, which is called by its inventor, t a guillotine valve. Tins now and patented design has many interesting features, and important 'claims are made, for its possibilities as a means of improving engine performance (states Jhe As evervoho knows, the valve geai has a pronounced .influence upon the power output, of on engine, and one of the principal difficulties is to pi ovide for, a sufficiently, easy-flow .of the ceases into,, and out t of* the cylinders at high revolution speeds. It is also true that the hot area represented by the conventional exhaust valve limits the scope of designers by preventing them from using-still higher compression pressures. The compressed mixture receives, heat from this source which increases. , th-e, likelihood of detonation and rough running. . . The guillotine, valve is of semi-circu-lar form, two suOh components. being located in the cylinder head. They are caused to slide up and down, in order to control a series of inlet and exhaust ports, and it is obvious,that the port area cap readily be made .very much larger than hi a conventional engine. The operating gear, consists of a pair of rockers (for each cylinder) to lift the valves, springs to return them, and an overhead camshaft. This system is thought to lie . suitable for large-bore engines, blit for a small motor car pow.er unit the inventor,, suggests .the alternative of push-rod operations from a camshaft placed in the crankcase, . .. , Another p.Oint which, has a hearing upo)i gas, flow is, that the initial upward movement of the guillotine valve is masked by the slot in which it is guided. Consequently, the - cams can be arranged to give quite a low degree of acceleration, favourable to quiet running and moderate w stresses, without sacrificing the rapid opening of the port which is so desirhblo for efficient gas flow at high speeds. It is also clear that any desired degree of overlap in the valve timing can readily be obtained.

IRON, STEEL, OR ALUMINIUM. As compared with a sleeve, the guillotine valve lias the advantages or a much lower weight and of a location which does not present any interference with tho flow of heat to the cylinder walls; experiments may show that it can be made of aluminium alloy for high-performance engines, although either iron or steel might be found preferable for power units of the motor car type. The inventor considers that the considerable degree of . valve cooling which can easily be provided would obviate any difficulties with distortion or lubrication. When closed, during the compression and firing strokes, the valves lire well supported along their lower and upper edges, and are also retained by the ribs which divide the pairs of ports. There would seem to be no difficulty in arranging for ample water-cooled surfaces; lubricant could be introduced along the working faces of the valves and controlled by expanding rings resembling piston rings. With theSe precautions it is thought that the effort required to move the valves would be quite small. They would carry a considerable load during the compression and firing strokes, but would then be stationary; by the time that the initial movement of the exhaust valve occurred the pressure in the cylinder would have dropped to quite a moderate figure. As full-scale experiments have yet to be made it is not possible to give any performance figures or to do more than forecast the probable durability of these valves in service or the relative cost of manufacture. They do, however, appear at present important advantages. From the maintenance standpoint there is the obvious convenience of being able to decarbonise the Combustion chamber and piston top through the open ports (after removing the manifolds) without taking off the cylinder head. Valve grinding, and trouble with pitting, burning, and hammering would also be obviated.