• New Suspension in 40-ton Trailer
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Small-diameter Rear Wheels and a Patent Form of Suspension are Notable Features of a Trailer Specially Designed for Service in South Africa ACRANKED-FRAME trailer of 40-ton capacity, and having an unsual design of suspension, has recently been completed by Cranes (Dereham), Ltd., for the City of Port Elizabeth, South Africa. A low-loading vehicle suitable for the transport of transformers and other heavy electrical equipment was called for. The vehicle had to be built for side or end loading, preferably without removing the rear bogie, and spring suspension and solid tyres were required.
32 Tyres
To comply with these requirements, very small-diameter rear tyres were needed and it was decided to fit tyres of 22 ins, diameter and 5 ins. wide. Twenty-four of these tyres carry the rear load; they are arranged in triple formation on eight wheels. With this arrangement a deck height of only 2 ft. 4 ins, when laden is achieved. Front tyres of more generous proportions are fitted, eight of them being mounted on four hubs in a single row.
The rear suspension is the point of major interest, and a patent has been applied for, to cover this design. The eight wheels are arranged in two rows of four, there being two wheels on each of four axles. Each axle has a wheel at each end and a boss at its centre. This boss is bored and bushed to fit on the journal of a large radius arm, so that it is free to rock, and thus distributes the load evenly on both wheels. There are four radius arms, all of which are pivoted on .a single cross-shaft, which is
attached to the trailer frame by means of brackets. The two radius arms on each side form in effect a rocker beam jointed at its centre, and are designed so that the journals taking the axles on their ends lie on a common longitudinal centre line.
Beneath each of these pairs of radius arms is a leaf spring. This spring has no eyes, but fits at each end into a shoe, which is a part of the corresponding radius arm and at its centre is clamped to a seat on one of the radius arms of the pair Thus, on each side of the trailer there is a complete assembly free to rock on a cross-shaft, and on each of these assemblies are two axles, one in front and the other behind the cross
shaft, both of these axles being free to rock on journals on the radius arms. Spring-controlled relative movement is possible between the two radius-arm journals of one pair.
This suspension design has the advantage that the springs arc relieved of all side and end stresses, and carry only a vertically acting load. Furthermore, it is compact. In this case the wheelbase of the rear bogie assembly is only 3 ft. The height from the ground to the attaching face of the cross-shaft brackets is about 1 ft 7 ins, when laden. Thus, in side elevation the complete assembly is smaller than the average hics,cle. The inner wheel track is 2 ft. 14 ins, and the outer track 6 ft 10 ins.
Front Suspension
he front suspension is of the Crane patent standard four-in-line trunnionended spring type. The spring-pivot brackets are mounted on a fabricated forecarriage comprising a rectangular frame with a circular fifth wheel and having at its centre a large-diameter cast. steel kingpin. Manganese-bronze wearing strips are provided on tha lower fifth-wheel ring.
Welded construction has been used for the main frame, the members of which are rolled-steel channels reinforced by plates.
Mechanically operated brakes are fitted to all wheels. The front brakes are of the two-leading-shoe type, 161-in. diameter, and are operated by a cable from the tractor. Those at the rear are 14-in, diameter and are applied from a hand wheel at the front of the trailer.
Ramps can be fitted at any point along the length of the trailer. Jacks are supplied to support the rear or side when loading. On the front deck a Thompson 7-ton winch is mounted.
'The machine is being supplied through J. H. Plane and Co. (Pty.), Ltd.. Johannesburg, Crane South African agent.
Further trailers having the same design of suspension, but fitted with 32-27-in. by 6-in, pneumatic tyres, are now in course of production. These also are destined for South Africa