FRONT-WHEEL DR
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,ND LOW LOADING.
Putting the "Horse" Before the "Calt."
Immis portant_ Advantages Likely to Accrue from an opment.
IT has always been the policy of this journal to investAigate thoroughly the possibility of any
• improvements that can be made to commercial vehicles, and, without unduly flattering ourselves, we may say that we have, in the past, been instrumental in eausipg attention to be• given to several useful and highly successful projects. The need for improvement extant in commercial vehicles at the present time demands that all potential avenues should be explored, ..and in this connection, therefore, we may well discuss the possibilities of frontwheel drive.
Primarily, the duty of the commercial vehicle , chaSsis is to carry as great a load as conveniently as is possible. Several considerations crop up—for instance, the load should be carried as low as is convenient, so that, in the case of passenger-carrying vehicles, top-deck weatherproof covers can be very easily employed.
Advantages of Low Chassis,
We have emphasized in a previous article the dedesirability of obtaining a low chassis, and, apart from the question of wheel, size only, it must be admitted that the fact that the transmission has to be located underneath the load platform of a vehicle raises the height of that load platform very appreciably.
IS there not a strong case, therefore, to be made for the development of front-wheel drive? Let us °aline the design of a vehicle employing such a system and discuss its advantages. By driving direct from the engine to the front axle, the weight of a considerable length of transmission is eliminated, .making . the vehicle as a whole lighter. The mechanical lay-out would comprise a normal-type engine built in unit construction with a gearbox at its forward end, and this gearbox casing might also enclose a differential gear and a -transmission brake. From the differential, two universally jointed shafts would run to the two front wheels, a convenient form of axle . being the old De Dion Bouton type, in which there is a load-carrying member distinct and separate from that portion which transmits the drive. There would not be any • undue complication in/making the wheels that drive act as steering members also. The radiator could conveniently be mounted in the normal position and the driver' could sit alongside the power unit, so that the whole of the rearward -space would be available.
' At this point, the side members of the chassis could well curve down, and, be it noted, the body would be mounted direct on to the chassis, there being no need to make any provision for the mechanical parts to be inspected, for all that would exist between the Nont and back axles would be a pair of brake-operating rods running to-ordinary drums on the rear wheels. The chassis frame itself would not ,be more than " onestep " high off the ground, and on a frameworksof this type it should be a Simple matter to mount a convenient douBle-deck body with all seats enclosed, while for goods carriage such a construction would be BN very acceptable to those concerns which deal with milk, refuse, cable-drums, light but bulky articles, and in all other -cases where A low load-line is desirable.
The employment of a transmission brake together with ordinary brakes on the rear wheels would result in four-wheel braking being effected in a very simple and comparatively cheap manner. There would, it is true, be slightly more weight on the front axle, but this would be desirable owing to the • fact that wheel adhesion for the drive would, have to be obtained.
It is by no means without interest to observe that at a meeting of the L.A.E., at which the question of six-wheeled vehicles was discussed, a gentleman who has had much to do with four-wheel drive vehiclet gave, as his conviction, the fact that a machine that was driving on its front wheels did far less road damage than did one that drove in the normal manner only. We a-re always keen on furthering the production of a non-road-destroying vehicle, and if merely on this score alone, the front-wheel-drive type outlined herewith should be worthy of investigation.
From the purely theoretical point of view, or, perhaps, it may better be said, -from' the point of view of those who like to consider basic facts, the system of front-wheel drive hag much to commend it. Clearly to grasp the° following statements, imagine: an automobile to be an oblong, squaresectioned mass that has to be forced by power over an irregular plane—representing the road. With an ordinary rear-wheel-drive vehicle the propelling fore is applied at a point mid-way between tho two rear wheels. Any resistance that the front of the vehicle may have to forward motion, if it is not acting directly in line with this point, results in the mass having a tendency to sheer off its course. Once the front of the vehicle is pushed out of straight the driving forcer tends. to increase the deviation, and in practice this resuits in a driver having to decfultch, and so eause.cessation of the transmission of power.
It might be thought that this trouble is more theoretical than practical; but any lorry driver .admit that he is far more concerned with the difficulties involved when a front-wheel skid is experienced than is the case when it is merely the back of the vehicle that slides. At the same time,' every driver knows that so Soon as askid of any nature is involved he 'must shut off his engine, as otherwise the driving force, acting out of line with the desired: direction•of Progress of the vehicle, will emphasize the skid, possibly with disastrous resuit.s.
Greater Stibility.
again taking our oblong mass imagine it to be pulled instead of pushed, as would be the case were front-wheel drive employed. It is now in a state of stability, as opposed to the state of unstable equilibrium which is produced by the driving force when applied at the rearward end. Therefore, it can reasonably be supposed that _a properly designed vehicle-which drives on its front wheels, or, in othet words, pulls its load, would be more inamenvrable, more stable, and, more easily. handled than would one of the present normal type.
This problem of front-wheel
skids is rapidly approaching serious dimensions. The presentday seven-ton commercial vehicle carries a very big proportion of its total weight. on its rear wheels. Thus, the load on the front wheels is comparatively light, and hence their adhesion becomes insufficient to provide the necessary reaction for -steering. This weight disposition is usually brought about, inter ?Ilia, by the fact-that a considerable proportion of the weight of the transmission, as well as of' the load, is imposed upon the rear wheels of the ordinary rear-driving vehicle ; but with the chassis form outlined on this page it can easily be seen that practically the whole of the weight of the engine, gearbox, .flnal drive, differential, ete., etc., is taken on the front axle. .
,A point in this connection that most certainly concerns the lighter.
types of commercial vehicle is the fact that the unsprung weight of the back axle is a-ppreeiably lower than is that of ordinary normal types, and as the efficiency of any automobile suspension system is in a large degree a 'function of the unsprung weight, it follows that the springing or the load carried by a front-drive vehicle must be appreciably superior to that of one that incorporates a back axle that may weigh anything up to 14 tons, this mass being necessitated by the fact that it has to deal both with load-carrying and powertransmitting duties. - The front-drive vehicle, we
admit, is by no means new, but we do emphasize that at the present stage of development it is well worthy of further consideration. The advantages, both -theoretical and practical, that are outlined arobve are too numerous to be overlooked.