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Variable Compression Engine

18th January 1957
Page 66
Page 66, 18th January 1957 — Variable Compression Engine
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THE compression ratio of an engine has to be designed with regard to the maximum possible cylinder charge, but as the average engine runs at part load for most of its working life, a reduced efficiency results. A novel scheme by which the compression ratio is automatically adjusted to the optimum value, whatever the load, is shown in patent No. 762,074 (The British Internal Combustion Engine Research Association, 111-112 Buckingham Avenue, Slough).

The essence of the scheme is that the piston is made to be variable in length, so that at light load it will approach the cylinder-head more closely and thus raise the compression.

Each piston is made in two concentric parts, the upper one comprising the crown, the ring region, the skirt and a bottom, screwed assembly ring (1). The lower portion contains the gudgeon-pin assembly and is essentially a piston within a piston, being fitted with sealing rings at points 2. 3 and 4.

Change in working length is effected hydraulically; if liquid be introduced into space 5 between the two components it will lengthen. A safety valve (6) limits the pressure between the two members and in consequence limits the maximum compression.

The entry of oil is automatic, a pumping action being created by the reciprocation of the piston acting with the inertia of the oil. A one-way valve connects an oil-filled annulus (7) to the upper chamber and a small but steady flow of oil creeps into the latter, lengthening the piston by a few thousandths of an inch on each stroke.

The piston shown is also oil-cooled, the oil being circulated from the gudgeon-pin supply via passages (8) in the crown.

REAR AXLE FOR INDEPENDENT SUSPENSION

PATENT No. 761,942 shows a design for a driving axle of the type employing swinging half-axles. Its chief advantage is that one less universal joint is needed. The patent comes from Daimler-Benz A.G., Stuttgart-Unterturkheim, Germany.

In this scheme, the crown-wheel and differential assembly are mounted normally (I) so that only one universal joint (2) is needed for the two halfaxles. The two half-assemblies pivot about a pin (3), rubber bushes being interposed. This pivot is housed in a casing attached to the superstructure of the vehicle.

NOVEL UNIVERSAL JOINT

PATENT No. 762.305 (Morris Motors, Ltd., Cowley, Oxford), discloses details of a novel universal joint. Its main purpose is said to be for incorporation in a steering mechanism, but no further details are given of this.

A chief feature of the joint, which is of the Hooke pattern, is that the pivot bushes (I) are made of nylon and are, surrounded by pre-compressed rubber bushes (2). The nylon bushes are split longitudinally so that the pressure of the rubber tends to close them in on the pins and thus prevent slack from developing. This ensures a long-life joint that needs no lubricating.

TYRE FOR SOFT GROUND

SOFT tyres give better traction on soft ground, but as under-inflation causes much damage, this solution is not very practicable. An improved tyre for this duty is shown in patent No. 762,496 (N. McLeod, 45 2nd Street, Oakville, Ontario, Canada).

This inventor proposes three separate chambers in the tyre, as illustrated in the drawing. Each chamber has its own inflation valve and three differen1 pressures are used. The inner one is inflated hardest, the middle one to an intermediate value and the outer one the least. In one example mentioned, the three pressures would• be in the ratio of 4 : 2: 1 respectively. The tyre may thus be run at a low pressure in the groundengaging area, yet be adequately protected by the inner pressures from damaging deformation.

DUAL-PURPOSE COUPLING

A HYDRAULIC coupling which also ri acts as a torsional shock-absorber is shown in patent No. 762,487 (T. Hindmarch, Undo Lodge, Stanley Avenue, Chesham, Bucks).

An outer casing forms the driving member and is provided with an internal gear-ring (I). The driven member is a disc having recesses in which are placed planetary pinions (2). These closely fit their surroundings and act as gear-pumps. One liquid port is in the side (not shown) the other being in position 3.

In operation, if the liquid circuit be unobstructed, the coupling is free. By restricting the flow, however, it will take up the drive until total obstruction is reached; this gives a hydraulic lock apart from slight, inevitable leakage.

An automatic spring-loaded valve controls the liquid circuit. It is made so as to be open at low pressure and also at high pressure, with a closed position in the medium range. This provides the vibration-damping action because such vibration consists of alternate pulses of high and low pressure. The liquid used is heavy and viscous and is unaffected by heat.

A VEHICLE-WASHING MACHINE A MACHINE for washing vehicles is 1-1shown in patent No. 760,163, the chief feature of which is the method adopted for cleaning the sloping front. No extra brushes are needed, the front being reached by moving the other brushes in a controlled path. (R. Emanuel, 7 via Canova, Turin, Italy.)


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