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To Prevent Vacua in .

19th June 1942, Page 36
19th June 1942
Page 36
Page 36, 19th June 1942 — To Prevent Vacua in .
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Hydraulic Brake 'Systems

A Résumé of Patent Specifications That Have Recently Been Published

I T is of vital importance that in no circumstances may air, even in minute quantity, enter an hydraulic brake system, and patent No. 544,669 shows a scheme whereby this condition is fully satisfied. The patentees are Bendix, Ltd., and J. Irving, both of King's Road, Tyseley, Birmingham.

The risk of air entry is usually at tts greatest after a sudden release of the -brakes; at this moment, owing to the inertia of long pipes of fluid, a local vacuum may be created. The invention aims at abolishing this, by creating a slight • " hang-over" of presswe in the system, so that sc-ne little time elapses before atmospheric pressure is reached.

Referring to our sketch, which depicts a master cylinder according to the invention, the plunger (4) moves to the right through a sealing washer (3) to force fluid out of the discharge port (2) into the pipe line. At the same time, fresh fluid flows into the space (5) behind the plunger from the

reservoir pipe (6). On the return stroke, however, the fluid ir the rear chamber (5) is throttled by a discvalve (1), which permits free entry but restricted return. The working pressure therefore subsides slowly and unwanted suction is avoidied.

By means of slots in the plunger, space 5 can replenish the working circuit on the return stroke as well as when the plunger is in the off position. thus preventing a negative pressure from being established in the pipe lines.

HYDRAULIC-BRAKE PRESSURE ' STEP-UP DEVICE

UTODERN conditions and heavy alvehicles call for considerable braking effort, and this tends towards the use of high hydraulic pressures. The latter, however, may give trouble from leakage, abnormal wear of the cup washers, and expansion of tlle pipe lines. To reconcile these conflicting factors is the object of a device shown in patent No. 544,552, by the Ben.dix Aviation Corporation., South Bend, Indiana, U.S.A.

It is proposed to employ a relatively lowlressure in the master cylinder and the pipe lines, and to provide a step-up device to each wheel cylinder. The device can be inserted or removed with out any structural alterations. Fluid _ from tile master cylinder enters at 3 and acts upon the larger end of a . two-diameter piston (2). The smaller end moves in a reduced cylinder and steps up the pressure in the wellunderstood manner.

A point of interest is that the device also gives a two-speed effort, that is, the low pressure can at first penetrate to the small cylinder via a bore (4), which contains a pushrod to hold open the ball valve (5)

So ,soon as the piston moves, the ballvalve seats and the device acts as a booster. The strength of the piston. return spring governs the pressure_ value at which the step-up comes into action.

Note that the screw thread of the pipe end (3) -is similar to that on the cylinder end (1); this is to allow the booster to be removed and low pressure to be used in the brakes if desired. The patentee recommends that this be done on the front wheels of a heavy vehicle on very slippery roads. EXHAUSTING INTO CRANKCASE FOR SILENCE AND EFFICIENCY NAANY attempts have been made to iV1 recover some of the energy wasted in exhaust gases, and patent No. 544,443 shows another scheme of this nature, although the first claim relates to silencing. The patentees are F. Butler and E. Kite, 38, Victoria Street, Westminster. It is proposed to transfer the exhaust gas from one cylinder to the crankcase, where its remaining pressure can be used to assist the upstroke of another piston.

In this scheme the engine must have one or more pairs of pistons working in unison over a common crankchamber ; the usual four-cylindered engine consists of two such pairs, and could be used provided cylinders 2 and 3 Were given a partitioned-off crankcase, whilst the crankcases of cylinders 1 and 4 were also sealed and interconnected.

Dealing with a pair, on the opening of the exhaust valve of one cylinder the gases are transferred to the crankcase and oxe5t upward pressure on the underside of the two pistons, one of which has the same pressure above it as below it, whilst the other is under the load of the new charge of gas that is being compressed.

The drawing shows the transfer port (1) leading to the crankcase, and a rotary valve (2) for the ultimate disposal of the exhaust gases. We question the advisability of-discharging hot gases into the crankcase.

NEW IDEAS IN SELF-SEALING TYRE TUBE CROM the Dunlop Rubber Co., Ltd.,

and others, Dunlop House, Albany Street, London, comes patent No. 544,670, which shows a self-sealing inner -tube capable of dealing with large punctures, such as may be made by bullets and the -like. The patent states that a normal inner tube, being when inflated in a state of' tension, tends to permit the enlargement Of a hole by tearing, and it is, therefore, necessary that a self-sealing tube should have its outer surface in compression, so that the sealing action is assisted.

The new tube is made with a double wall, the outer one being larger than . normal, so as to be compressed in the cover. The inner one is inflated i,n the usual manner. Between the two walls are separate chambers, as shown in section in an accompanying drawing. The chambers are filled with sealing solution, consisting of some tacky viscous substance. Several examples are mentioned, notably glyptal resin and a permanently adhesive substance marketed under the name Vistanex.

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People: F. Butler, E. Kite

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