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The Forrest Gearless Motor Hansom.

21st May 1908, Page 14
21st May 1908
Page 14
Page 14, 21st May 1908 — The Forrest Gearless Motor Hansom.
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Keywords : Gear, Drive Shaft, Tatra T813

A Description of an Eight Horse-Power Friction-Driven Machine which sells at 200 Guineas Complete.

Any new petrol-driven chassis, whether it be for a commercial vehicle or pleasure car, if it possess a frictiondriven change-speed gear, is liable, in its infancy, to suffer from a somewhat unreasoning distrust on the part of the purchasing public. The discs will slip; the range of gear ratio cannot be large enough ; the end thrust necessary to obtain adhesion must be tremendous: these are all criticisms which are immediately launched against the unfortunate manufacturer, and they are criticisms with which Messrs. J. A. Wade and Company, of Forrest Street, Liverpool, the manufacturers of the Forrest gearless chassis, are only too Commencing, therefore, with a carefully-acquired knowledge of the inherent faults of some of the existing systems, Mr. Wade, the designer, has evolved a small machine which is at least remarkable for its simplicity and, of course, its resultant low price. It is not much exaggeration to say that the mechanism comprises little else than an engine and a back axle. Two hundred guineas is the price asked for a complete cab, and at that price it is fitted with a two-cylinder, 8-91a.p. engine. Its price and simplicity are sufficient excuse to warrant a careful examination of the chassis. The makers have a confirmed aversion to the description " friction-driven chassis "; they prefer to describe the variable-gear mechanism as a " rollingcontact drive." This rather implies a distinction without a difference, with the exception that the latter title is, perhaps, more descriptive. The principle underlying this particular design of variable gearing has been to secure constant pressure between the surfaces in contact, by the provision of a springloaded device which automatically cornpen sates for inequalities of surface of the discs, or imperfections of alignment. To this end, the surfaces are normally held up to their work by the pull exerted by two comparatively small coil springs (E), which keep the surface pressure constant. It is claimed that the elastic pull exerted by the springs obviates excessive end thrust. In some early designs of friction

driven (sic) variable gear, the pressure between the transmitting surfaces has been secured by the definite and fixed operation of cams, toggles, and other inelastic devices. Messrs. Wade and Company admit that they do not consider a drive of their pattern would be satisfactory for large powers, but they state that, for small powers, such as those required for cab work, there is no practical objection to the securing of such a simple solution of the variable transmission problem. Cab work, in London at any rate, should not require a greater range of speed than there is provided by the variation of gear ratio secured with this disc drive, which is, in the makers' opinion, sufficient for all normal employment in the Metropolis.

The line drawing of the chassis plan clearly indicates the arrangement of the chief components. A two-cylinder, inclined-type engine is slung on the near side of the front of the frame, with its crankshaft parallel to the axles. A steel disc (A), ao inches in diameter, takes the place of the flywheel, and the end thrust resulting from the pressure between the driving discs is absorbed by a five-inch, Hoffmann, thrust ball-bearing(L) mounted on the engine case itself. The movable disc (B) has its periphery formed of four leather rings on edge, and the makers claim that these can be replaced in 15 minutes at a cost of seven shillings and sixpence. Each set of leathers is supposed to last 4,000 miles.

The variation in gear is effected by depressing a pedal (D), which pulls the disc (B) away from the face of A, against the action of the controlling springs, and by sliding the smaller disc across the face of the larger one, the springs (E) re-engaging the friction faces on releasing the pedal. A stop is fitted to prevent the change-disc (B) from being shifted too far over on to the reverse side of the engine disc (A).

The whole of the sliding disc, squared shaft, and operating gear is mounted on a swinging frame (C), which is moved back bodily, against the action of the springs, by the pedal action, through a rack and pinion device, which is not shown in either the drawing or photograph. Provision is made for holding the " roller-contact " discs out of engagement when they are relatively in the neutral position, i.e., when the edge of the small disc faces the centre of the large disc.

The power is transmitted to a stifflyconstructed live back axle of the bevelgeared type, through an articulated propellor shaft. The bevel reduction on the back-axle is 6 to x, although, owing to the small engine power provided, the makers are willing to fit a 7 to r gear if it is necessary for the cab to carry luggage, or to tackle hilly districts.

The engine has a bore of 84rnm., and a piston stroke of rromm. The two independent connecting rods act upon a single crankpin. The crankshaft is made in one piece, and runs in unusually long bearings. The cooling is arranged on the therrno-syphon system ; an unusual feature is, however, introduced in the provision of separate intake and outlet pipes for each cylinder. Every care is taken to avoid the possibility of getting grease on to the driving surfaces, and oil is used on no other part of the chassis than the engine, which is provided with a pump lubricator. The usual brakes on the back wheels and propellor shaft are provided.

The makers have had a number of their small pleasure cars running satisfactorily in private service for long periods, and they will be pleased to refer to their owners anyone who is likely to be interested in the adaptation of these simple and cheap machines to the requirements of the London cab trade.

Tags

People: A. Wade
Locations: Liverpool, London

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