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THE FREE WHEEL IN THE TRANSMISSION LINE.

10th January 1928
Page 63
Page 64
Page 63, 10th January 1928 — THE FREE WHEEL IN THE TRANSMISSION LINE.
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The Vulcan Free Gear Now Developed for Employment on Commercial Motor Vehicles. A Brief Description of the Device.

Fr HE free gear, free wheel or over running device has attracted a good deal of attention in. the private car industry, but up to the present we have not heard much of its actual use on commercial vehicles. The Commercial Motor has often in the past pointed out that the most likely solution of the change-gear difficulty would be some form of clutch situated between the gearbox and the rear axle. We consider that such a device is even more necessary with the heavier types of vehicles than with the private car, as gear-changing with them is more difficult on account of the heavier gears and clutch employed and on account of the rapidity with which a heavy vehicle will lose its momentum when it is found necessary to carry out the operation of changing-down on hills..

.Many letters have appeared in the private-car journals from people who have never tried such a device and have not even grasped the first principle involved, often confusing rate of acceleration with rate of rotation. In their ignorance they have imagined all sorts of terrible things happening, and their foolish fears may have affected others. We are glad, therefore, to herald the fact that a real business has commenced with this promising innovation, The Vulcan free gear consists of a unidirectional drive which is always in operation in the transmission line between the gearbox and the rear axle. The line drawings and the photographic views show the separate parts, the working of which can best be seen in the line drawings. In the sectional view the shaft (E) is that which extends from the gearbox, and has spline(' to it the member (B), which is provided with a number of tangential flats arranged as shown in the other line drawing. The member (D) is forced so that it extends in a bell form over (B), the space between them being occupied by the rollers, which jam when rotation is in one direction, but release their hold when rotation is reversed or when tha driven member overruns the driving member, thus providing a unidirectional drive, or what is generally known now as a free wheel. The shaft extending from (D) carries a universal joint which connects it to the drive of the rear axle.

This provides a simple and silent means whereby the vehicle can over-run the engine at any time. There are, however, occasions when a free wheel may not be desired, and there is the means for reversing to be provided for ; it is for this purpose that the sliding member (A) is introduced. This member has buttressshaped teeth set so that they can be brought to engage with similar teeth on the member (D), and when these teeth are in engagement the drive is no longer unidirectional but is bidirectional, driving as if the free wheel were not there.

The lever shown in the photographic views actuates the sliding-toothed member (A); bringing it into use when required.

We cannot say that we agree that a positive dog engagement for this purpose is an ideal one, as in the hands of an unskilful driver it might be jammed in whilst the vehicle was running at a high speed and whilst the engine was merely idling or had stopped . entirely. The result of this .would, of course, be unpleasant, so we have pinned our faith to some device that would enable the drive to be changed to a bidirectional one, such as a friction clutch, which would give a more gradual engagement than could be obtained by dogs. Time and experience alone, however, will prove whether it is safe to employ the dogs.

As many of our readers may not be fully aware of the advantages claimed for the free gear we will endeavour to make the matter clear. The device has two main objects. The first is the making of gear changing such an easy matter that a novice can change from one gear to another without acquiring the skill necessary to operate ordinary gears. The other object is to save fuel by taking advantage of every decline or other circumstance which will enable the vehicle to travel without the aid of the engine and; whilst doing so, to enjoy the gliding motion of a vehicle travelling at a high rate without the vibration of a fast-running engine and without undue exhaust fumes and their consequent obnoxious effects.

It may be said that this can be done by'holding out the ordinary clutch, but this is not the case, as to hold a heavy clutch out for long is tiring, whilst the clutch withdrawal mechanism is often not suitable for holding out for a prolonged period, and one does not, therefore, take advantage of every small decline or occasion where free-wheeling can be indulged in, but

with a unidirectional drive the vehicle automatically does this for the driver.

An the time that free wheeling is going on there is a saving not only of fuel but of wear and tear of all engine parts ; the engine does not suck up oil and thus over-oil the plugs, and the silent, gliding motion adds a new pleasure to riding in a bus or coach.

To return to the matter of gear changing, it may be asked : "110w does a free wheel make this an easier operation?" The answer is that by interposing a free wheel the propeller shaft is prevented from driving the gearshafts, so that when the ordinary clutch is withdrawn and its speed slightly checked by means of the clutch stop one has two shafts in the condition that neither is under the influence of any kind of drive, but merely spinning of its own momentum and declining in speed. It will not be difficult to see that the gears on shafts running under these conditions can be changed without skill or noise. It is well known that damage done to gears by unskilful drivers is a very serious item in maintenance costs, so that any device which will reduce the expense of this item should be appreciated by owners of vehicles of all types.

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