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IMPROVING the BREED
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of the British Passenger Vehicle
How Attention to Details of Chassis Design is Producing a Vehicle of Superior Performance and Greatly Improved Maintenance Record
NEW forms of transmission to replace the familiar gearbox, and new positions for the power unit ,(particularly the side mounting), are steps towards the development of an entirely new form of passenger vehicle. At the present stage t is a little difficult to see what the result will be, but all are agreed that real scope is offered in both the directions named.
In the meantime, however, detail improvements and new ideas of a less spectacular nature are definitely improving the breed of the British vehicle in a manner which is most gratifying to the operator and the maintenance engineer. .
It does one good to look into current design changes with a practical eye and to see how British passenger vehicles, single-deckers and double-deckers, are being made easier to drive and to maintain, safer and more capable in traffic conditions, more wear-resisting and generally more economical.
Except for improved lines, the normal bus of to-day looks outwardly so like the bus of three years or four years ago that it is necessary to point out what is happening in designers' offices: This will particularly interest our many overseas readers.
Since long life has been the mainstay of arguments in favour of paying a higher price to get a British vehicle, let us consider, first of all, the steps that are being taken to ensure stilt longer life. We must remember that two indirect benefits result from longer life of the component. One is the synchronizing of docking periods for different parts of the chassis—a big factor In fleet maintenance—in fact, a subject that is only just becoming understood.
E26 The other is the avoidance of adjustments during service.
Hardened cylinder liners are giving longer life between reboring, but few realize the attention that is now devoted to piston-ring design and the fact that hardened piston rings are being commonly used by the best engine makers. A.E.C. units have screwed-in valve seats and a Leyland feature is the use of Stellite-faced seats for exhaust valves. Not only is the hammering of the valve resisted, but metals are chosen to withstand the corrosive action of exhaust flame; such ma terials are used by the Morris-Commercial concern.
Large, renewable fabric filters for the lubricant are improving the working conditions of the engine, and bearing metals are being improved—in Thornycroft engines, to mention but one instance. In the Leyland oil engine, a case-hardened crankshaft has been adopted. Five-speed gearboxes make it possible to reduce crankshaft speeds, points that are emphasized by the Bristol and Gloucester concerns.
In .brake drums and brake facings there is considerable progress to report. The employment of thicker facings up to in (on A.E.C. vehicles) gives a longer fife, and this is assisted by the practice of utilizing a single pair of wide shoes in the place of narrow
double shoes. With thick facings, adjustments, of course, are necessary, but simple and effective automatic devices, such as used by the A.E.C. and Moths-Commercial companies, maintain a standard clearance.
The entire facing can be worn away without the need for packing plates, although in the case of the Morris-Commercial Imperial double-decker provision for such plates is made to allow for increasing the drum diameter due to subsequent retming. In this way brake-shoe facings may last out the period between engine dock overhauls.
Quite a good feature is the use of shackles fitted into the split and clamped housings to preVent wear in the brackets and shackle links and to simplify replacement. The point is noticed in the Guy Arab chassis, among others.
Longer life of clutch surfaces is extending the period between overhaul, and improved design is increasing the period between adjustments, a good example being the Dennis 429 clutch, so named because it has a friction area of 429 sq. ins. The use of a thicker clutch facing on Leyland doubledeckers is resulting in as much as 75,000 miles' useful work on ordinary city duty.
Materials to revised specifications are featured in the Kanier models, in which nickel-chrome molybdenum steel is used for parts that are subjected to extra fatigue stresses. Even details like rounded splines mean longer life, and these have been adopted in the Leyland fully floating axle, which, incidentally, has worm centres of 7i ins:, so as to give good wearing qualities.
Oil glands that do not wear out and so save expensive dismantling work are a detail that becomes important, and good results are being. obtained from bellows-type oil glands, such as are used on A.E.C. chassis.
:Long life avoids attention, but where this must be given sensible steps can be taken to facilitate it. Easily replaceable radiator sections and tubes (on Dennis and A.E.C. vehicles respectively) are a case in point Reference to this feature reminds one that, on Crossley vehicles, either unit construction o r separate disposition of engine and gearbox are optionally available. Guy and Albion chassis afford examples of separate gearboxes that are edsily removed downward, thus facilitating attention to both gearbox and clutch. Movable front cross-members to enable power units to be withdrawn, as on Guy, Sunbeam, and other chassis, save time.
Reduction of weight and of wasted space enable more work and revenue
• to—be obtained from -die modern chas sis. Lightness is being secured by close attention to detail ; for example, the use of Elektron for crankcases, gearboxes, worm cases, etc., and of silicon aluminium alloy for various parts; also the employment of light, but immensely strong, tubular cross-members.
Seating space is increased on:frontengined as well as side-engined vehicles, and the new Leyland has its front body,
bulkhead 6i ins, farther forward. The front of the Sunbeam petrol engine was specially redesigned to economize in length, and in the Dennis Ace, which, with an 11-ft. wheelbase, seats 20 passengers, the front axle is set back and the engine is placed close up to the radiator.
Another aid in this respect is the use of longer springs and their positioning under the frame members to give greater base width. Frame alterations to suit the needs of the bodybuilder, thus permitting reduced body weight, are a feature of current Karrier design, and their scope is recognized by all makers. The improved Bristol body mountings prevent drumming with metal-frame bodies. Before long we shall probably see independent front-wheel springing, and this may ease the task of designing satisfactory front body mountings.
Power, performance and economy are improved by the use of five-speed gearboxes, and improved engines make possible higher axle ratios with rechosen gear ratios. These improved engine performances are being obtained partly by down-draught carburetters, that on the Dennis Ace, for instance, giving more power as well as economy.
Finally, we come to refinement, and one of the leading current modifications is the use of rubber engine mountings and rubber-bushed universal joints, although smoother running engines and more accurately balanced transmission members render such devices less necessary than they were in the past.
It is probably in the direction of refinement that the interest in the new transmission developments, and in side engine mountings. is centred.