ADVANCES IN PETROL VEHICLE DESIGN.
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Improved Brakes, Engines, Tyres and Suspension. Increasing Use of Tractor-lorries. Developing the Light Van Chassis. Lower Loading Lines.
DURING the past twelve months there has been an activity in commercial vehicle design unparalleled for many years. This activity has been shown in all spheres, petrol, steam and electrically driven vehicles having each made considerable advances. Limitation of space makes it impossible to do more than review the developments which have taken place in the field of the petrol engine in this article.
In view of the tendency to construct vehicles capable of carrying heavier and heavier loads at considerable speeds, the problem of providing really
efficient brakes, capable of bringing the vehicle rapidly to a stop without imposing undue effort upon the driver, has become a very vital one. The braking question is of additional importance when the tractor-lorry or the lorry and trailer are considered, owing to the difficulty of providing • a sufficiently flexible mechanical brake connection. In this and other respects, the pneumatic means of brake operation possesses many outstanding advantages, and it is interesting to notice that the Westinghouse system is making great progress and has been adopted by the. Associated. Equipment CO., Ltd., for their new tractor-lorry, whilst the Sentinel Waggon Co., Ltd, have introduced a ,vacuum-operated brake for their new large-load carrier:'
For four-wheel lorries, the use ofpneumatic or hydraulic brakes is ,on the increase, but mechanical operation still 'holds the . field. In Continental designS,.the tendency is to .reduce the labour involved on the part of the driver by the provision of a servomechanism' in which the, braking effect is enhanced by the movement of the vehicle itself: Four-wheel brakes constitute another important development. The braking effect obtainable by applying frictional resistance to the rotation of the rear wheels only is definitely limited by the adhesion between the tyres and the road. The adhesion available on the rear wheels only amounts to about 50 per cent. of that obtainable from all four wheels, owing to the fact that when the lorry is slowing down the weight is thrown forward, increasing the load on the front axle and reducing that acting on the rear axle. Consequently, ,it can safely be said that the retardation obtainable is doubled when a four-wheel braking system is substituted for the two-wheel system. In addition, the possibility of skidding on a greasy surface is definitely minimized. Turning to the power unit, there are several interesting lines of progress to record. For vans of from one pr-two tons capacity, ,capable of fairly high speeds, the overhead-valve engine is -becoming increasingly popular, the valves being usually operated by push-rods from a canashaft housed in the crankcase. Overhead camshafts have also been used.
The orthodox side-by-side-valve engine with detachable head is, however, holding its own, particularly in the larger sizes. Whilst the outward appearance of power units of this type may not show much alteration, progress has been made in internal design conducive to more economical running. Combustion chambers, for example, are now usually made of such a shape that the troublesome knocking tendency caused by low grades of petrol is minimized. Mr. H. R. Ricardo has, of course, been foremost in research in this direction, and has definitely laid down the best form of combustion chamber for engines of the side-valve type. Reducing knocking tendencies increases the power available from cylinders of any given capacity, and permits a slightly higher compression pressure to be used with economical results.
Carburation has also received attention, and it is now generally realized that some form of pre-heating is necessary with present-day commercial spirit. In this connection the advance made in the designing of carburetters for the use of paraffin should not be overlooked, excellent results having been obtained with the Commer design. _ Although not of idamediate interest, the work which has been proceeding with a view to the adaptation of the oil-injection engine for use on the road is of considerible importance. That more progress has not been made is probably due to two deterrent factors : the present superabundance of petrol, and the impression, justifiable or otherwise, which certainly exists, that, so soon as fuel oils come into general use on motor vehicles, the price will be greatly increased by the controlling companies. Nevertheless, progress in this direction is to be commended, and engines of the oil-injection type have the great advantage, for Colonial usage, that they will run satisfactorily on any of a very wide range of semi-crude oil fuels. This is due to the fact
that the fuel is injected into the cylinder itself1 and is both vaporized and ignited there, no preliminary carburation being required.
Next in order come the improvements effected in the insulation of the chassis from road shocks. Here, there are two lines of defence : the tyres and the spiings. As regards the former, the primary developments to record are the increase in the use of semipneumatics, containing air at atmospheric pressure, and the increasing number of makers producing tyres of this type. For .many years the N.A.P. has been successfully employed, and now there are several other interesting types available, such as the Aero'cord and the Trublpruf.
For heavy vehicles, a single wide solid-band type is gaining in popularity at the expense of . the twin variety for rear wheels. The so-called " giant pneumatic" has not met with the immediate 'widespread success which some enthusiasts predicted, but, nevertheless, has become popular with many coach Owners.
While the semi-elliptic leaf spring still holds the field, several interesting modifications can be recorded. For example, a number of devices have been brought out which make the leaf miring selfadjustable in accordance with the load. In most of these arrangements the spring comes against earns as the load increases, the virtual length being thereby decreased, so that the spring becomes stiffer. The Ferodo system of providing fabric strips between the steel leaves of the spring is another point of interest, rusting of the leaves being prevented and easy working assured.
Several devices have been produced for insulating the body from shocks transmitted to the frame through the tyres and the main springs. It will be recalled that, in the Holden system, an inflated tube is placed between channels secured to the frame and the body respectively. In other designs a set of small leaf springs is interposed..
With regard to the advantages of the multiwheel vehicle, it will here suffice to record the progress made by the six-wheel tractor-lorry. The scope of these large vehicles has been increased by the fact that all types of body can now be obtained, including endand side-tippers. A tractor-lorry passenger bus has actually been constructed by the Carrosserie Latymer, and will be brought into use when legal sanction is obtained. Considerable improvements have been made in the turntable connection between the tractor and trailer portions of the vehicle, with a view to improving stability and increasing the handiness of the vehicle. To prevent the rearmost wheels from cutting-in when cornering, a design was brought out, a short time ago by the Carrosserie Latymer in which the rearmost axle is pivoted and actuated by rods, swivelling automatically when corners are negotiated. A newcomer is, of course, the powerful and welldesigned A.E.C. 12-ton tractor-lorry, with a Westinghouse braking system. The economical running obtained with large vehicles of the tractor-lorry type is truly remarkable, and the ratio of pay load to unladen weight is extremely good. This, of course, means that comparatively little petrol is consumed in moving the chassis
itself from place to place, the fuel being usefully expended in shifting the paying part of the load,.. Calculated on a gross-load basis, over one hundred ton-miles per gallon have been recorded:by many users.
At the other end of the commercial vehicle scale, we find increasing attention is being given by manufacturers and users to the claims of light chassis of the motorcar type for conveying loads of 5 cwt. to 10 cwt. at high speeds. There are many newcomers
in this field, including English, Con tinental and American makes, most of which follow orthodox passenger motorcar practice.
One of the moat striking trends of the past twelve months is the lowering of the loading line. This movement•has consistently been fostered in this journal, because the lower. the platform (in the absence of a suitable . loading dock). the easier does loading and unloading become. underslung springs, with downswept frames, dropped axles, and double-reduction final drives have been employed to lower the platforms of orthodox vehicles. Other designers have gone still further, reconstructing the whole vehiale, an
example being the B.D..2-ton.ner. •
A front-wheel drive possesses marked advantages in this and other respects, as .eexiiplified by the remarkable American vehicle recently described in this journal. This eight-ton lorry, then described, had many other remarkable features, one of the most interesting being the power-operated' steering. With vehicles' of this type actually, in use at .the present time, one is led to wonder whether the heavy multiwheel lorry of .the future will be provided with a servo-motor for steering, power-operated brakes, and either -an electrically operated gear change or an automatic torque converter. The driver of such a vehicle .e..otild-have less to do than the man who con
trols a locomotive. • A remarkable. revival of, interest has recently taken place in -the problem of abolishing the gearbox. While there is no iiinnediate prospect of the advent of the infmitely variable gear or torque converter for general use, there • is nb doubt that, with so many engineers independently working on the problem, it can only be a matter of a few years before the orthodox gearbox, with its three or four separated ratios, is superseded. .
This. is a raatter of very great importance to all who use the petrol engine on the road. A feature of all engines of this type is that the torque or twisting effect delivered to the clutch is almost•the same for all normal speeds at full throttle. As the torque required to move the vehicle, applied to the rear wheels, is continually varying, owingto changes in. the road surface, gradient and load, it follows that, when only three or four individual ratios or reductions are available, the engine is not running under ideal conditions for the greater part of its time on the road.
Furthermore, there is the trouble of gear changing to consider, and the harm that can be caused by an inefficient driver when handling the gear lever and clutch. Missing the gear on a hill and running back out of control is quite a common cause of serious accidents; arid we are always astonished at the attitude of the user towards the .sprag. If it is fitted by the makers, the user removes it, and it would almost seem as if, in order to ensure the presence of a sprag and• to make sure that it is alwa.ys in working order and available, some form of compulsion may be' neces sary. It follows that, in order to meet the requirements as completely as possible, the torque converter should, adjust itself automatically in accordance with the load and the output, of the engine ; this, of course, is a feature of the system invented by Mr. Constantinesco.
This device possesses the additional advantage of a spragging effect, which would prevent the vehicle from running back down hill. The desirability of incorporating a sprag in the transmission system has been pointed out in this journal over and over again.
In connection with infinitely variable transmissions, the claims of the petrol-electric vehicle must not be overlooked. Chassis of this type have, of course, been successfully produced by TillingStevens, Ltd., for many years, and possess numerous unique advantages. Apart from infinitely-variable automatic transmission, and the petrol-electric system, multi-speed mechanical gears are worthy of mention, although these necessitate control by the driver. Sewn {Speeds are ingeniously provided on the 2-i-3-ton G.M.C. chassis shown at Olympia, by
means of a two-speed layshaft.
Among the novelties, the remarkable chassis desoribed in our issue dated October 16th, 1923, is worthy of mention. In this vehicle a four-wheel drive is provided, and, in addition, all four wheels are available for steering. It will be recalled that by means of a simple adjustment the wheels can be so coupled that the vehicle will move sideways, crabfashion. This feature would prove very useful in the case of a lorry sandwiched between two others the driver of which wished to move, outS of the line. Another interesting feature is the suspension, which is'self-adjustable according to speed and load.'