Commercial Motor Vehicles

An example of this type of lorry is the Mammoth Major of the Associated Equipment Co., Ltd., Southall, Middlesex. It is built in two lengths of wheelbase, 2131 and 2251in., and is equipped with a six-cylinder Diesel (heavy-oil) engine of 7.585 litres (462 cu.in.) displacement, developing 102 h.p. at 1,75o r.p.m. ; a four speed gearbox, a two-speed auxiliary gearbox with a 1.58:1 low gear ratio, and a 7.9 double-reduction drive to the forward one of the two rear axles. Net chassis weights are 11,300 and zi,9oolb. for the short and long model, respectively.

Introduction of four-axle or eight-wheel lorries in Great Brit ain was followed there by the development of a new type of six wheeler with four front steering and two rear driving wheels.

This has the advantage over the older type of rigid six-wheeler (with two front steering and four rear driving wheels), that it gives rise to less scuffing and wear of tires in turning corners, as illustrated by the accompanying sketches. In order that there may be no side slip or scuffing of any of the road wheels when the ' vehicle describes a curve, the axes of all of the wheels produced must meet in a common point (or must intersect a single vertical line), which is the instantaneous axis of the vehicle's path. The sketches show that this condition can be fulfilled in a vehicle with four steering wheels, but not in one with only two steering wheels, as the axes of the four non-steering wheels are parallel and therefore never meet. In the drawings, 0 represents the centre of the turning circle.

Effect of Legislation on Design and Rating.—Legislation has had considerable influence on lorry design and rating in Great Britain. Under the Road-and-Rail-Traffic Act of 1933, all motor lorries using the public highways must be licensed by the Ministry of Transport. Three types of licences are issued, viz., "A" licences for lorries in public-haulage service over unlimited distances; "B" licences for lorries in public service in restricted areas, and "C" licences for lorries to be used only in the businesses of their owners. Between 1935 and 1938 the number of "A" and "B" licences extant was reduced by about 17,000 (9%) to reduce competition with the railways ; during the same period the number of "C" licences increased approximately 61,000 (20%).

Lorries are taxed on the basis of unladen weight, and the speed limit also varies with this weight. For instance, in 1939 a vehicle weighing not over 21 (long) tons, unladen, was subject to an annual tax of £30 and was allowed to travel at a maximum speed of 3o m.p.h., while heavier vehicles paid a higher tax and were restricted to 20 miles per hour. For this reason great efforts were made by British lorry designers to increase the ratio of pay load to unladen weight. In 1931, before the new regulations came into force, lorries of 2-1- tons unladen weight usually had a pay-load rating of 2 or 21- tons, but in 1939 they had ratings of as high as 5 tons.

A lorry designed for maximum pay-load capacity to come within the 21-ton tax-and-speed class is the Dennis 5-tonner brought out in 5939. It had a four-cylinder engine of 3.77 litres (23o cu.in.) piston displacement, developing 75 b.h.p.; a four speed gearbox, a rear axle driven by 7:1 spiral bevel gears, disc wheels with 32x6-in. tires, a track of about 65in., and a wheelbase of either 116 or 162in., the shorter chassis being intended to re ceive a tipping (dump) body. Chassis weights of 4,280 and left ample margins for bodies within the 21-ton unladen weight limit.

Passenger Vehicles.

Before 1918 chassis employed for mo tor-buses and coaches were similar in most respects to standard ton goods vehicle chassis. As the demand for increased speed and comfort became more insistent, designers had to find means of lowering the centre of gravity, lengthening the wheel base and effecting improvements in springs, brakes and steering gear. Engines and driving gears had to be quieted and made more efficient, and as each new model was produced, the platform level was lowered. No sooner had designers produced a reasonable type of chassis for solid tires than users began to demand pneu matics. Designers were then faced with fresh difficulties, but by 1935 this class of vehicle left little to be desired in the way of safety, comfort, speed and economic running, many saloon buses engaged on inter-urban service being most luxurious. (An inno vation in England in 1928 was a London-Liverpool night passenger service, using sleeping coaches, fitted with berths and toilet accommodation ; an attendant pressed clothes, served morning coffee, etc., while the inclusive charge was the equivalent of the 3rd-class rail fare.) Apart from strictly engineering details, pneumatic tires con tributed to the improvement of these vehicles, and by their absorption of road shocks permitted the use of lighter and im proved coach work, the construction of which has become as much an engineering as a coach-building matter, because of the extensive use of pressed steel and aluminium panels, brackets, etc. During the same period the design of taxicabs made relatively little progress, but this was due to police regulations which were formulated in the earliest days of motor-cars, and their enforce ment prevented the adoption of modern chassis designs. More over, the market being a small one, few makers were tempted to build them and the result was stagnation in design. (See also OMNIBUS.) Motor fire-engines have almost completely ousted horse-drawn steam-driven fire pumps, and as a general rule they are driven by a powerful petrol engine, through a special design of gear-box which permits of the power being transmitted either to the road wheels or to a rotary pump, generally of the turbine type, be cause of its high efficiency, and the fact that when drawing from a hydrant the initial water-pressure in the main is fully utilized. (See also FIRE-ENGINE.) Among vehicles specially designed for municipal purposes the Karrier and the Pagefield are examples. The former is a machine which sprinkles and sweeps the road and automatically collects the dust into a tipping body (Plate, fig. 2). It is operated by one man, is capable of easy manoeuvring and consequently may be employed at all hours of the day or night without interference with other traffic. The Pagefield machine is intended primarily for the collection of house refuse and consists of a wagon with a telescopic tipping platform, provided with elevating screws and winding gear. Refuse is collected in horse-drawn low-built con tainers and at predetermined stations a wagon arrives with an empty container, the wagon platform is tipped, its telescopic ramps extended and the empty container lowered. After this the full container is hauled up into its place and then lowered to the travelling position for conveyance to the refuse destructor or tip.