A Medium-capacity SIX-CYLINDER BUS CHASSIS.
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Details of the Vulcan Duchess Model, a Chassis of High Performance Designed to Carry 26-seater Bodies and Suitable for Long-distance Travel.
MHE Duchess chassis for passenger • work has just been added to the Vulcan range of high-efficiency sixcylinder chassis. Designed for bodies with a seating capacity for 26 passengers, it takes its place between the Duke model (for 20-seaters) and the Prince model (for 32-seater8). There is also the Princess, a 36-seater bus chassis, the four models covering the full range of municipal and privatecompany requirements for single-deck passenger vehicles. All of them have six-cylindered engines.
The Duchess chassis is especially designed to obtain a very low loading height, the lowest permitted by the Ministry of Transport regulations, which require a ground clearance of at least 10 ins, for a length of 14 ft. 6 ins, from the front of the chassis. The frame is therefore upswept 34 ins. over the front axle and 6/ ins, over the rear axle, giving a loading height of 214 ins. Frame members of ample depth are provided, and give to an engineer the impression that a load considerably greater than that specified could be carried with safety.
The Power Unit.
The power unit has a bore of a ins. and a stroke of 41 ins., giving a capacity of 3,880 c.c., the R.A.C. rating being 25.35 h.p. It develops 30 b.h.p. at 1,000 r.p.m., 58 b.h.p. at 2,000 r.p.m., and 70 b.h.p. at 3,000 r.p.m., a performance which gives good hill-climbing and very useful speed on top gear. The valves are overhead, operated by push rods. The cylinder head is detachable and a cover encloses the valve gear. The magneto and dynamo are mounted on the near side, the latter being so arranged that it may be with
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drawn from the crankcase without dis
turbing its silent chain drive. The carburetter is of the vertical type, mounted on the same side of the engine, and the induction is jacketed by the exhaust manifold. The crankshaft, a heat-treated stamping, is borne in four white-metal bearings, as is the camshaft. Cast-iron pistons are employed, with three rings, the connecting rods being duralumin stampings of H-section.
Engine Auxiliaries.
Lubrication on this engine is of the conventional kind, with gear-type pump skew-driven from the crankshaft, and incorporating a pressure filter which is easily accessible for cleaning. The oil capacity is about 2 gallons. Chassis lubrication is by grease gun throughout.
There is a centrifugal water pump, driven in tandem with the dynamo. The fan is belt-driven, and mounted with ball bearings upon an eccentrically adjustable spindle. The clutch is of the dry single-plate type.
The gearbox is bolted to the rear of the clutch casing, thus forming a unit with the engine, which is suspended at three points in the frame. Four speeds forward and a reverse gear are provided, the shafts being mounted on ball bearings. The forward gears give the following ratios of speeds at 1,000 engine revolutions per minute, when 36-in. by 6-ia. tyres are fitted :—
Top (6i to 1) ... 15 m.p.h.
3rd (11 to 1) 8i m.p.h.
2nd (16.9 to 1) 5/ m.p.h. 2nd (16.9 to 1) 5/ m.p.h. 1st (34.2 to 1) n m.p.h.
The gear change is centrally located, with a safety catch on the lever for reverse gear. This brings us to the rear axle, which is of the full-floating type with an overhead worm drive and 6i to 1 reduction. The road wheels are mounted on caststeel hubs with large diameter roller bearings. The drive is conveyed by an open tubular shaft supported at the centre by a self-aligning bearing carried in a frame cross-member of ample section. A fibre universal joint is fitted behind the gearbox, and the final section of the propeller shaft carries two universal joints of the star type. enclosed and running in oil. The front axle is a stamping of the I-section type, with wheels mounted ordinarily on roller bearings.
The braking on this chassis is amply efficient, and, in conjunction with a lively six-cylindered engine giving gc od acceleration, it affords pleasant and safe driving. The brake pedal operates, with servo-assistance, expanding shoes on the front and rear brake drums, whilst the hand lever operates upon the rear drums only.
Low Loading Height.
The effect of the upswept frame members is aided by underslung semielliptical springs, producing a satisfactorily low loading height Steel disc wheels are fitted for pneumatic tyres, sized 32-in. by 6-in., twin tyres being fitted on the rear axle. The steering is of the cam-and-roller type, which is Particularly comfortable with pneumatic tyres, a point of great importance with a fast six-cylinder chassis. The petrol tank is fitted at the off side of the frame, has a 20-gallon capacity, and supplies through an Autovac placed on the dash.
At a recent trial run in wet weather over a hilly route a Duchess chassis
with a fully loaded 26-seater body averaged 21 wisp.h. for 70 miles without any attempt at making a good time for the distance. Several steep gradients were included in the route selected, ranging from 1 in 15 to 1 in 6, and calling for full use of the gearbox. The weather was wintry, and the benefit IA the Ki-gas injector was appreciated, for instant starting was obtained from void, the electric starter working well. The makers are particularly proud of the ease of control of this bus and of its stability on the road. A vehicle of this kind, with a six-cylindered overhead-valve engine developing as much as 70 b.h.p. at 3,000 r.p.m., must have no tendency to /jolt when cornering at proper speeds, and must have an easily handled ateering wheel, free from vibration, •to give the confidence of control demanded by its acceleration and braking. The low centre of gravity and well-designed steering and braking arrangements of the Duchess chassis seem to give all that is necessary in this respect, so that speeds exceeding 40 m.p.h. are attained without danger or any sensation of discomfort.
The standard design of body for this chassis is a saloon bus for 26 passengers with a folding entrance door at the front operated by a lever within easy reach of the driver. The driver is partitioned off and comfortably seated with all controls nicely at hand.