Front Stairs; Forward Engine; 77 Seats

The Guy Wulfrunian Air-Suspended Bus Chassis

by John M. Dickinson-Simpson

Extracts from a technical leaflet issued by Guy Motors in 1959

Guy Motors Limited claims to have introduced the most technically advanced passenger service vehicle yet made available to bus operators. The claim is not altogether an idle boast, for whereas there are some continental and American bus chassis with air springs and independent front suspension, there is no production chassis offered which allies these features with disc brakes.

Those same basic features of air suspension and disc brakes also, of course, apply to the Guy 'Victory Airide' single decker chassis introduced at the last Earls Court Show. But with the 'Wulfrunian' chassis, Guy has gone further. All lubrication points except those on the propeller shafts have been eliminated. Successful efforts have been made to lighten the steering without the introduction of power assistance. Various air pipe lines have been grouped together as far as possible and are to be coloured for easy identification. A Cave-Browne-Cave combined saloon-heating and engine-cooling system which eliminates the usual radiator has been incorporated. And the brakes are operated by solid-line hydraulics right to the footbrake pedal: failure of the air-pressure assistance will not destroy the foot brake action.

However, it is the overall concept of the 'Wulfrunian' that has captured the imagination of those British operators who have been in on the design from the beginning and have offered their advice.

The chassis has been designed in the first place for a 30 ft. long, front entrance, low height, 75 to 77-seater double decker body with a flat lower saloon floor, and a centre aisle upper saloon seating layout.

An entrance anywhere else along the length, other than the front could be accommodated, or indeed a front entrance in combination with a rear exit, as is favoured by one or two British municipalities and is popular overseas as a single-deck layout.

The engine.

As such it is expected to have appeal for city bus operation where a single step, a constant-level flat floor and a wide entrance might be expected to result in considerably improved passenger flow, and thus offer operational advantages offsetting the loss of at least four seats on account of the inevitably deep front wheel arches.

The engines offered as the standard alternatives are the Gardner 6L W 8.4 litre (358 lb-ft. maximum torque), the Gardner (6LX l0.45 litre (485 lb-ft.), the Leyland O.600 9.8 litre (410 lb-ft.) and the Leyland O.680 (450 lb.ft.). All are well-proved six-cylinder direct injection diesel units. The Gardner engines, though lighter than the Leylands, are not as compact.

To permit a gangway to the back of the bus on the same level as the rest of the lower saloon floor, the rear axle is of the step down double reduction variety. The primary reduction is through spiral bevel gearing and a three star differential, from which shafts transmit the drive via a pair of steep angle helical gears to the hubs, which are packed with high melting point grease. To take the end thrust arising from the big helix angle (chosen to promote quietness), the final reduction gears revolve on taper roller bearings, as do the hubs.

Heat flow to the hubs from the disc brakes is minimised by an air gap between the cylindrical sleeve on the end of which the disc is cast. At the rear the discs are also slotted radially both to reduce weight and to induce a flow of cool air across the hub, through the disc and out between the twin tyres. To assure good heat conductivity in the Chromidium cast iron discs themselves, they are sand cast and thus have a transverse and random distribution of long graphite flakes to conduct heat rapidly from the outer surface of the disc to the interior.

Rear axle location is primarily by parallel trailing links.

Air suspension development at Guy Motors has now reached a virtual end. As a result of three bright ideas, for which patent applications have been made, the Guy design team claims to have solved the air suspension problems of frequency control, bump-through at the diaphragm units, and roll stiffness. Full details will not be released at this stage because Guy feels it has a substantial lead over others in air suspension development. The broad idea is, however, that Guy's own levelling valves increase or decrease the pressure in the suspension diaphragm according to the load imposed on any particular corner of the chassis. The valves act instantaneously and thus enable the suspension to deal with comparatively sudden load changes as experienced when going round a corner.

As well as looking after the comfort of the passengers, the designer has made efforts to lighten the task of the driver. In particular much research has been done on steering. The latest ideas on geometry have been exploited and as a result the front wheels have a 1 degree negative camber. Changes in castor and kingpin angles have been made to reduce as much as possible the vertical lift of the wheel as it is turned. Maximum use is made of the inherent self-centring qualities of the tyres themselves. Six and a half turns of the steering wheel are required from lock to lock. The turning circle is 62 ft.