BETTER SPEED WITH THE CREEPER TRACK.
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Both on the Highway and Across Country the Speed of the Creeper-track Vehicle is Increased in the Case of the New 14 h.p. Crossley-Kegresse.
FOR work in undeveloped country -I-' the need for special vehicles with means for driving over extremely rough and soft ground has caused attention to be devoted to the consideration of the actual form of the driving medium. Hitherto, the horse has solved the problem, but one of the greatest steps towards mechanical means for transport over such ccountry is the introduction of the Kegresse creeper-track. As is now fairly well known, the principle involved calls for a rubber band which passes over two pulleys, the part of the band in contact with the ground being so loaded that a very large proportion of its length Is in full contact with the surface no matter how irregular it may be.
A description of the CrossleyKegresse model was given in the i&sue of The Commercial Motor for March 2nd, 1020. Since then, however, various tests have been carried out and many refinements made in detail, but the general construction and proportions of the vehicle remain the same as when they were given about a year ago. Tests have been carried out on a chassis fitted alternately with a boxvan-type body and a touring body, the results being very interesting, considering the extremely difficult country which has been successfully negotiated and the general road-worthiness of the vehicle when used on more normal road surfaces.
Before describing the .actual performance in the field, as it were, a brief description of the chassis may not be out of place. With a wheelbase of Ott. and track of 4 ft. 8 ins., quite a large body space is available, and, by virtue of the essentially low construction of the framework and the absence of wheel arches, a low loading-level for the vehicle is obtaMed, even when equipped with a body.
The power unit is a development of the popular Crossley. 14 h.p. car engine, which is housed in a special three-point suspension arrangement in order to avoid distortion of the bearings when traversing extremely rough and tortuous surfaces. The power unit comprises the engine, a single-plate clutch and four-speed gearbox which, in conjunction with a two-speed box attached to the driving axle of the creeper track, pro vides eight speeds, ranging from 109.93 to 1, on the lowest ratio, to 5.03 to 1 on the highest ratio.
With a capacity of 2,388 c.c. the cylinders are cast en bloc and have a bore of 80 mm. and a piston stroke of 120 mm. Side-by-side valves awa employed, and are totally enclosed and automatically lubricated, whilst an easily detachable cylinder head enables the process of decarboniza-, tion and valve grinding to be carried out without dismantling a large number of parts.
Both the crankshaft and camshaft have three main bearings and the big-end bearings of the former are fed by oil under pressure from a plunger-type pump, thence by drilled passages. A relief valve is incorporated in the lubricating system, and the gauge situated on the instrument board gives the driver instant warning of any development of trouble. The quantity of oil in the sump can be determined by an inspection of a gauge on the near side of the sump casing in close proximity to the pump and filter, -access to the latter being obtained by removing the plate beneath the pump depression.
The vehicle is fully equipped for electric lighting and starting, both
dynamo and starter motor being attached to the engine body by flange mountings; the dynamo is positively driven by triangulated timing chain. The clutch has fabric friction discs and is .easily adjustable, whilst the spring pressure is self-Contained and a ball-thrust bearing is employed for withdrawal ; the spigot is fitted with a ball bearing.
The main gearbox is contained in an aluminium casting honed direct to the bell housing of the engine, and provides four forward speeds and one reverse. When used in conjunction with the auxiliary box—which, incidentally, is operated by a separate lever—eight forward speeds are obtainable, the top and bottom, as already mentioned, being 5.6 to 1 and 101.93 to 1, whilst the intermediate ratios are roughly, 10 to 1, 16 to 1, 24 to 1, 26 to 1, 43 to 1 and 68 to 1. In addition, two reverse gear ratios are provided, the higher being 22 to 1 and the lower 92 to 1.
In order to provide a means whereby the vehicle may be extricated from an especially awkwarl position—say, when one track is located on particularly soft ground and the other one is on hard ground —a differential locking device is fitted, so that both tracks can be locked together and all the drive taken through one side, at the same time preventing the other track from spinning.
Eight bogie wheels provide the drive to the ground, the large-diameter wheel at the rear merely forming the drive to the track from the axle. The rubber composition track has a herring-bone tread about 5 ins, wide, practically the whole of the drive being taken through . the vee-sectioned portion of the inside of the track running in a yea shaped groove on the pulleys. In order to prevent slip, the outer
members of the rear pulleys are connected in the hub by a pair of circular sleeves having cone dogs meshing with each other, so that, immediately any tendency for the driving member to revolve independently of the outer driven member shows itself the dogs move in relation to each other, thereby pressing the flanges of the pulley into closer contact with the vee-driving portions a the track. Each pair of bogies can, of course, lock vertically and angularly in relation to the other, so that the track can take up
any position required by the e1igencies of the surface over which it is passing.
In order to test their product, Crossley Motors, Ltd„ have leased a piece of ground where practically every type of going is included in some part or other. Actually, the land was previously a grouse shoot located in a particularly wild part of the country, where ditches, extremely steep hills, slippery grass banks, etc., abound in plenty. With a full load of 20 cwt., the Kegresse track will propel the vehicle through particularly sticky mud—so deep that it reaches the hub caps—with certainty, and is at the same time able to restart under such severe conditions. On one part of the course there is a stretch of grass land with a gradient of 1 in 21. The Kegresse track provides sufficient grip and the engine suffleient power in order to climb it without trouble, although chains, which can be used with the track, are necessary. On easier gradients, however —say, 1 in 5—even though they have a very slimy surface, successful climbs have been made without the use of chains, the herring-bone pattern on the tread of the tracks, when the tracks slip, actually flinging the mud outwards until a hard bottom is reached.
Water, too, has no deterrent effect on the grip of the track upon either the driving pulleys or the surface of the ground, as a ford 22 ins, deep has been successfully negotiated without any sign of trouble. This is undoubtedly due to the fact that the area of the track in contact with the ground is so large, and the actual load per sq. in. of track surface is, in consequence, very small. The disparity is so great between the Kegresse track and the ordinary solid or pneumatic tyre that no comparison could reasonably be made.
On the highway, 30 m.p.h. is well within the capabilities of the vehicle on top gear, whilst, on this gear, too, hills of the 1-in-12 variety can be climbed without appreciable slackening of Speed. On rough going, the limitation to speed is not actually the capacity of the vehicle, but the capability of the human element in withstanding shock. One interesting point concerning maintenance is the fact that the tracks are extremely easy to remove for replacement or repair, the outer flange of the idler pulley being capable of being removed easily by unscrewing a worm contained in the idler pulley itself (by means of a key inserted in the radius arm), when the track can be slid off the top and a new one fitted in lieu.