OVERSEAS DEMAND INFLI
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3' ES HOME DESIGN
A Review of Improvements in Vehicle Design Made Since the 1948 Commercial Show. In this Article Advances in Engines and Gearboxes are Outlined
T the Commercial Motor Show in 1948, most manufacturers presented models embodying features dictated by overseas requirements Such vehicles were designated as being for export only, which meant that home operators had to forgo any benefit which they might have derived from the special details of design.
Prominent among these items were insulated cabs, power units of increased output, frames of more generous section, more powerful braking and details making for easier maintenance. One of the characteristics of the 1950 Commercial Motor Show is the influence which the export drive has undoubtedly had on home-market models, as a number of makes of goods vehicle is now available with airconditioned cabs or driving compartments notable for their spaciousness, larger or modified power units of greater output, frames which are deeper and with wider flanges, improved braking and other features which will prolong the periods between maintenance operations.
This is an important aspect of the 1950 exhibition. Of far greater significance, perhaps, is the break-away from conventional practice as exemplified in underfloor-engined chass:s, and the Foden with transversely mounted rear engine. These new models point the way to a new era in the history of the British passenger vehicle.
As a contrast in oil-engine size, there is the Rover Meteorite 250 b.h.p. 18-litre unit, as fitted in the Mighty Antar, and the Perkins P4 oil engine, ix hich produces a maximum output of 50 b.h.p. The P4 is fitted in the Seddon 3-tonner. Its power output is to be raised by using a fuel-injection pump with a high-lift camshaft, in conjunction with minor modifications to the induction s2,siem. The Perkins P6 already benefits by similar modifications, which have 79 b.h.p. raised the output of this unit from 70 to
The Thornycroft Nippy 3-tonner has previously been available only with a petrol engine, but this model is now being offered with a 4.14-litre oil engine. The unit is not a completely new design, but a direct-injection version of that employed in earlier models of the Sturdy chassis.
The Gardner LW series of oil engines, as fitted in Atkinson, Scammell, Foden, Guy, E.R.F., Tilling-Stevens. Vulcan and Unipower vehicles, has also been subject to design modifications, the result being an increase of about .n17,
10 per cent, in power output. Such a substantial increase in power by changes which do not affect basic design is of considerable significance as far as servicing and maintenance are concerned.
An improvement in oil-engine performance has been found to result from ensuring that only cool air is allowed to enter the induction. The Gardner 41K unit on the Guy Otter and the 6LW on the rear-engined Foden have extensions on the inlet manifold, the air inlets being well removed from engine heat. In the case of the Otter, ducting runs from the front panel of the cab to an air cleaner on the induction manifold.
The A.E.C. 11.3-litre oil engine, as used in the Mammoth Major, Matador Mark III and Maudslay overseas passenger chassis has the same overall dimensions as the 9.6-litre unit. In fact, the latter unit forms the basis of the larger engine. The smaller engine, suitably modified, is used in the A E.C. Regal Mark IV, the Crossley Mark IV and the 11Iaudslav Marathon Mark IV underfloor-engined chassis.
These three vehicles, which have many features in common, have an inbuilt device for lowering and raising the engine. When the engine mountings have been released, the unit becomes suspended from two chains anchored to the engine about its centre of balance. Tv, o arms, pivotally mounted on the left-hand frame member, serve to keep the engine steady as the chains are released through the agency of screw gear.
With a supercharger fitted, the Dennis 0.6 oil engine. which, in modified form, is used in the Dominant underfloor-engined chassis, produces 130 b.h.p. as against 100 b.h.p. for the normally aspirated version. To give a low floor line to the body, the unit has to be of minimum depth. and this has been achieved by removing the auxiliary drive from the back of the cylinder block to the front of the crankshaft and driving the fuel injection pump and corn pressor, or exhauster as the case may be, from opposite ends of the camshaft. Incidentally, this makes for improved accessibility to the fuel pump and other components.
In the Guy and Atkinson underfloor-engined passenger chassis, the power unit is the Gardner 6HLW, which is a modified version of the 6LW vertical unit, the engine offered as an alternative to the Foden two-stroke in that maker's rear-engined model. All the main components of the horizontal version are interchangeable with the vertical unit, an important maintenance feature where a mixed fleet of horizontal and vertical-engined chassis is operated.
Either the Foden or Gardner engine can be fitted into the Foden rear-engined chassis without alterations to the mounting arrangements. Slight modifications are, however, nezes
sary in respect of the connections to the radiator, which is located behind the engine. The exhaust of the rear-mounted Foden engine is silenced in three stages before reaching the atmosphere.
Interposed in the oil circulatory system of the Foden twostroke engine is a special radiator which is mounted on the side of the normal cooling unit. The oil, after leaving the pump, is fed to the radiator through a distribution valve. Following this it is conducted to filters in which a pressurerelease valve is incorporated. The distribution valve serves to regulate the oil flow, and is operative at between 80-180 degrees F. This oil cooler for the Foden unit is used only in the chassis where the engine is at the rear.
When Gardner,engined vehicles are operated in subtropical areas they also are equipped with an oil cooler. This takes the form of a number of flat tubes, arranged horizontally and carried in front of the normal water radiator. The E.R.F. 8-wheeler, built for operation in Australia with the Gardner 6 L.W. engine, and the Atkinson and the Foden tractors powered by the 8 L.W. unit, have this arrangement.
Low-pressure Injection The Aphonic low-pressure injectors now available on Leyland oil engines, are basically the Leyland high-pressure injectors, but set to 100 atmospheres and employing a More flexible needle operating op a Seating of smaller diameter. These modifications have resated in much quieter 'operation, the maximum pressure being lowered from 968 to 835 lb. per sq. in., without affecting the fuel consumption rate.
On the Leyland Royal Tiger chassis, 'air induction noise is minimized by passing air for combustion through a filter and boxed-in outrigger before reaching the induction pipe.
The Albion 9.9-litre 120 b.h.p. oil engine, as employed in the new H.D. range, now has a heavier timing chain of fin, pitch and crankshaft bearings of more generous area.
Both the new Dennis Falcon passenger chassis and the redesigned Centaur 7-tonner, have the Dennis 5-litre sixcylindered direct-injection oil engine. This unit, which replaces the 70 b.h.p. four-cylindered petrol engine, develops 75 b.h.p. at 2,000 r.p.m. The main casting of this engine can be turned, end for end, and the components arranged on either side to suit right-, or left-hand control.
The new Big Bedford, has a six-eylindered petrol engine which develops a maximurn of 110 b.h.p. M 3,200 r:p,m.; the net oetput, as installed, being 94 b.h.p. at 3,000 r.p.m.
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Push-fit cylinder liners are used, a feature that will considerably reduce engine-reconditioning time, as compared with reboring. The crankshaft journals are induction hardened, and steel-shell copper-lead-lined bearings are employed; crankcase ventilation is positively controlled. Included in the lubrication system is a detachable-element filter, ahd the filler, which is attached to the valve-rocker cover, is combined with the crankcase ventilation, oil-bath aCr cleaner.
One of the features of the Comtner 109 b.h.p. underfloor petrol engine is that it has chromium-finished cylinder bores. Experience having shown that this finish considerably extends bore life, the maker now similarly treats the bores of the 50 b.h.p. unit as used in Commer 25-cwt. forwardcontrol vehicles, and the process is extended to the power units of the Karrier range.
The most recent newcomer to the six-cylindered o.h.v. petrol-engined vehicle, is Morris Commercial Cars, Ltd., this maker hitherto having produced only four-cylindered units. The new unit is of 4.19-litre capacity, the R.A.C. rating being 28.81 h.p. With a 40 mm. choke, the engine develops 100 b.h.p. and in this form is fitted in the 5-ton chassis. In the 3-tonner, it is derated by using a 32 mm. choke, the output then being restricted to 70 b.h.p.
Of straight-forward design, this new unit has a fourheaping crankshaft crankshaft and a five-bearing camshaft, the latter
being driven by a duplex chain. Renewable exhaust-valve scats, pre-finished big-end bearings, and downdraught carburetter are features of the design.
The Trojan engine has been but little modified since it was first introduced, but a new form of combustion chamber permits low-speed idling without four-stroking. It is the only example of a two-stroke unit in which pumping cylinders are employed to induce the charge. The general design is unusual, in that four cylinders and four pistons are used. each pain sharing a common combustion space. The outstanding characteristic of the unit is its high torque at low speed.
Whilst the Renault rear-engined model is well known in its private-car form, this is the first time it has been offered in Britain as a goods-carrying vehicle. Although of only 760 c.c. capacity, its o.h.v. engine produces 19 b.h.p. at 4,000 r.p.m. It is mounted longitudinally in the chassis as a unit with the gearbox, the whole assembly, including the rear-axle half shafts, being remarkably accessible.
Considerable advance has been made in recent years in the design of gearboxes and final-drive systems, with the object of making better use of the engine power available. To this end, two-speed axles, hub reduction gears, auxiliary gearboxes and constant-mesh main boxes with synchromesh engagement are now more freely available. The only semi-automatic gearbox in a vehicle is that incorporated in the Dennis Dominant underfloor-engined chassis, the unit being made under licence from Hobbs Transmission. Ltd. Whilst the gear lever is retained, the foot-operated clutch is dispensed with. Embodying hydraulically operated clutches and torque-reaction brakes, the system has a fourspeed planetary arrangement, by means of which changes of ratio arc made silently and smoothly, regardless of engine speed. The ratio change occurs through torque action, which means that the gearbox automatically accommodates itself to the engine according to the conditions of operation.
The clutch transfer sequence does.not permit engine speed. to increase appreciably above that required in the gear being engaged. When engine speed is reduced to idling, the clutch in use automatically disengages, but because of the secondary pump installed, the engine may be started by towing or -n the overrun. Apart from the mechanical benefits derived from the Hobbs Transmission system, it will be appreciated that the driver is relieved of the need for employing any finesse in effecting a gear change.
Fluid coupling and preselective gearbox systems are available on such vehicles as A.E.C., Maudslay. Guy and Daimler. This transmission system is advantageous in affording a simple arrangement of controls for an amidshipsmounted engine and gearbox. In the case of the Guy underfloor-engined passenger chassis, in which such a system is used, a neat rod-and-lever relay is employed in the linkage between the selector lever and operating quadrant, further linkage being unnecessary as air pressure is used for busbar actuation. At its base, the selector lever incorporates a compensating gear, so that gear-lever travel is the same for all speeds.
Light Moving Parts
In the Albion H.D. range of vehicles, a new five-speed gearbox is now employed. It is of the constant-mesh type. with sliding-dog engagement. All the sliding parts are of minimum weight, consistent with strength, so that-the manual effort required to move the dogs in and out of engagement is commendably light. Another point is that gear-lever movement is the same for all gears. The gearbox case is a single-piece aluminium casting which is liberally ribbed for rigidity and sound-proofing.
Whereas the synchromesh arrangement for facilitating gear changing has been a common feature of the lighter types of vehicle based on private-car chassis, a number of makers of commercial vehicles now includes this simple device in their specifications.
It is not usual, however. to introduce synchromesh with constant-mesh trains, but this is being done in the new Bedford four-speed gearbox, in which third and second gears are so arranged. The gearbox is relatively short and compact, which make for weight reduction, rigidity and, therefore, quiet operation.
(To be concluded.)