THE DE NORMANVILLE SAFETY GEAR-BOX A CLEVER DESIGN WORKING ON THE EPICYCLIC PRINCIPLE, AVAILABLE AS AN EXTRA ON LARGER HUMBER MODELS.
IN the history of invention it frequently happens that two men striving to improve the same piece of apparatus will make use of the same principles, but the finished products each show advantages of their own. One pattern of epicyclic gear-box, the pre-selective selfchange pattern, has now been available for British motorists for several years, but it remained for Captain de Normanvine, whose name has been closely associated with motoring matters since the beginning of the century, to produce a ” direct-acting ” design, in which the gears are selected only as and when required. The de Normanville gearbox has been the subject of very strenuous tests throughout Europe, culminating in a trans-Sahara expedition in which the total weight of car and its associated trailer amounted to over three tons. It came through all these tests without the slightest trouble, and is now quoted by the Humber Company as an optional extra on the 16/60, Snipe ” 80 ” and Pullman models, priced at £30.
The usual epicyclic gear-trains are used for the three indirect gears. Top gear is a direct drive through a tapered Ferodolined cone, and in this ratio the geartrains are locked and rotate as one unit. Very high efficiencies are claimed in the indirect gears, 99 per cent. being obtainable on third.
The principal novelty of the invention lines in the fact of using hydraulic power to lock whichever train is required. A simple double-plunger pump worked from the input shaft forces oil to one of four plungers, and these, which are fitted with wedge-shaped shoes engage in grooves on the trains. No adjustment is required, for any slight wear is compensated for by an increased movement of the plunger. A positive method of disengaging the top gear cones is employed, and a springloaded hydraulic reservoir stores up sufficient energy to make eight changes of gear without starting the engine.
A single-plate clutch of normal design is interposed between engine and gear-box, and is so linked up that the gears cannot be changed until it is freed. This relieves the brake shoes from all strain except that of bringing the ‘trains to rest, while the clutch itself may be used for manmuvring in the ordinary way. The control lever is mounted in the centre of the steering column, and an unusual feature is the provision of two neutral positions. When the lever is in position ” N ” the clutch is held out, and all the components in the gearbox come to rest, preventing the rumbling sound often experienced with self-changing gear-boxes not preceded by some form of “traffic-clutch.” The other neutral position, marked ” C ” or coast is placed
above top gear, and simply frees all ratios in the box, and allows the car to ” free-wheel ” at will.
The de Normanville gearbox is handled in exactly the same way as the conventional ” clash-type ” except that double-clutching is never required. The clutch is depressed, the hand-lever moved to position “I,” and the car moves off when the clutch is re-engaged. To engage second gear the clutch is again depressed, the hand lever moved again, and when the clutch comes up again the car is in second gear.
We drove a short distance in a 16-60 Humber fitted with the new gear, and were delighted with the almost instantaneous yet perfectly smooth change, which gave this sturdily-built touring saloon almost the performance of the ” Snipe.”
The clutch action is no heavier than that of the normal single-plate device, since the power required for locking the trains is derived entirely from the oil pressure stored in the gearbox and altogether this new departure on the part of the Humber Company makes a valuable contribution to the world of motoring.
An interesting illustrated booklet showing the internal construction of the gearbox may be obtained from the Humber Company of Coventry, or from the London agents, Rootes, Ltd., Devonshire House, Piccadilly, W. 1.