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Control Valve tor Compressed Air Braking
Page 158
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A Résumé of Recently Published Patent Specifications
OPERATION of trailer brakes by —,compressed air is the subject of patent No. 602.485, which comes from Servo-Frein Dewandre S.A., Liege, Belgium. The patent. is chiefly con • cerned with the control valve operated by the driver's pedal.
It is necessary first to understand the action of the 'trailer braking system. This is powered from a compressed-air reservoir carried on the trailer, hut the controlling factor is a pipe system leading to the tractor, and operated, not by pressure. but by a fall in pressure. This means that should the trailer break away, the pressure-drop in the coupling pipe would instantly cause full braking action on the trailer.
The drawing shows the driveroperated valve for producing the opera tive pressure-drop. Main pressure is applied via the ;nlet (I) and passes through the cenue (2) of a piston (3) controlled by a pedal (4). The air . then passes through a port (5) and a pipe (6) and maintains the system in the non-operative zondition.
When the pedal is depressed, it pulls the piston up to a valvehead. (7) which then in effect, becomes part of the piston. This action cuts off the main airsupply, and causes the piston to " feel " the pressure and oppose the driver's effort. At the same time a valve (8) is pulled leftwards, opening an escape port (9) which drops the pressure in the trailer system and causes the brakes to be applied A slight end-play in the central valve-rod enables a state of equilibrium to be established at any degree of braking.
ONE-PIECE CLUTCH PLATES
THE usual type of clutch plate is one having a steel centre member with riveted-on friction facings, the reason being that the steel. and the friction
material have different functions to perform, and no one material can be found to do both duties. To employ a one-piece moulding for the plate is the aim of a scheme outlined in patent No. 601,790, by Ferodo, Ltd., and W. Hall, both of Sovereign Works,, Chapel-en-le-Frith, Stockport.
The drawing shows the component parts of the plate before being united. The rings 1 and 2 are made of suitable friction material, whilst ring 3 and a32
discs 4 and 5 are formed in a material chosen for its mechanical strength. The five pieces are then bonded into a unit by heat treatment, after which the centre is bored and splined. Details of the material are not given, except that it has a cloth base and is impregnated with suitable varnish. Although the proportions shown are not suitable for a motor vehicle, doubtless the shape could be modified for this purpose.
ELECTRO-MAGNETIC TRANSMISSION IMPROVEMENTS THE Cotal magnetic transmission is already well known, and the latest
modifications ate brought forward in patent No. 602,497, by Societe D'application des Brevets Cotal, Neuilly-sur-. Seine, France. Several designs are shown, the one illustrated being suitable for a heavy lorry. The main feature of the patent is not so much the changespeed mechanism as the clutching and reversing arrangements.
Referring to the drawing, the engine shaft ill drives, primarily, a magnetic clutch (2) and the sunwheel (3) of an epicyclic gear. The outer annulus of the gear forms the output shaft (4) whilst the planet-carrier (5), free on its shaft, can be magnetically gripped by either the primary clutch or by a stationary magnet (6). According to which magnet is operated, a forward or reverse drive is transmitted to the output shaft. A further feature is the provision of another magnet (7) which can grip the annulus member and function as an electric brake.
The rest of the parts are electrically operated two-speed gears: there are three sets of these, all coupled in series, an arrangement which, by selective clutching, will give eight speed ratios.
• THE HEAT-TREATMENT O‘F CARBURIZING STEEL PATENT No. 601.755 comes from Guy Motors, Ltd_ and W. Woodward, both of Fallings Park, Wolverhampton, and makes some suggestions on the subject of the case-hardening of alloy steels.
According to the patent, the usual treatment is as follows: The steel is first carburized for 12 hours at 900 degrees C., quenched at 840 degrees C., quenched again at 770 degrees C., and finally tempered for about lf hours at 170 degrees C. This method is rather inclined to leave a semi-soft layer just under the surface, where it is often exposed by grinding, the reason being that some of the austenite in the alloy has not been converted into the harder martensite.
The proposed remedy is to modify the heat-treatment to the following: First a normal carburizing operation and then to coal the piece to a sub-zero temperature immediately afterwards, followed by a temper ing operation. The 1 ow temperature mentioned is minus 75 degrees C., but no details are given as to how it is applied to the work.
TRAILER OVER-RUNNING BRAKES
TRAILER brakes, applied by over running, are open to the objection that it is impossible to reverse the outfit until the brakes have been manually released. To overcome this difficulty is the aim of a scheme shown in patent No. 602,525, by J. Isherwood, 16, Marsh Lane, Charlemont, West Bromwich.
To the drawbar is attached a sliding rod (1) which is spring-loaded at both ends so as to maintain the mid-position shown. Collars on the rod abut on a pair of forks (2) geared together by teeth (3), and one of them is lengthened to actuate the brake cable (4). A spring (5) normally applies sufficient force tb the brakes to keep them in the "on " position.
In operation, if the tractor pulls, the collar (6) presses on its fork and by overpowering the spring, releases the brakes. Conversely, backing the tractor moves the left-hand collar and fork, with the same result. A hand-lever (7) cad be used to release the brakes, the rod then being held by a spring catch (8) which latches behind the towing eye.