Steerable trailer is
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45ft long by Ron Cater
• A 45ft-long semi-trailer with a folding and extensible fifth-wheel and a two-position, steering tandem-axled bogie has been developed by Ronway Engineering Co. Ltd., of Southall.
The company's experiences in the haulage of bridge beams—up to 100ft long—have highlighted the lack of a versatile semi-trailer that will not only enable such indivisible loads to be handled, but which will permit the entire steering of the outfit to be carried out from the driver's cab. This and the need of such a machine which is also capable of accommodating ordinary return loads has resulted in the design and development of the new Ronway trailer.
Fabricated steel l-beams with 5in. flanges are reduced from 16in. deep over the middle section to 12in. over the running gear and fifth-wheel, forming the main frames. These are joined with 4in. by 2in. rolled-steel channel cross-members, pierced through the main frames and set at such a height that the 1.25in. longitudinal hardwood floor ranges level with the top flanges of the main frames. The rave-rails comprise two 3in. rolled-steel channels welded to form an E-section. These are faced outwards and are welded to the cross-hearers to provide a 1in.-high chock rail.
Steering is effected by the pivoting of the whole of the tandem bogie about a central kingpin. The bogie will swing through an arc of 45deg, giving 22.5deg of steering on either lock. Two kingpin locations are provided 8ft apart, the rearmost positioning the bogie so that the periphery of the back-axle tyres ranges level with the rear cross-member of the frame.
The bogie is steered by a double-acting ram linked between the main and bogie frames. The ram is powered by a 24V electro-hydraulic pump, controlled by two push-buttons in the cab of the towing vehicle. Power generated by the system is sufficient, if needed, to skid the whole bogie while under a full 20-ton load: this procedure, needless to say, is not to be recommended. Steering of the bogie can be undertaken only in the rearmost of the two positions.
To lock the bogie in line with the semitrailer framework, two mechanical locks powered by air-pressure diaphragm chambers are fitted. These hook catches are positioned at the off-side front and at the near-side rear of the bogie. When engaged, the shoulders of the locks engage the rubbing plates, preventing out-of-parallel running; the catches latch onto the underside of the bogie plate to prevent separation. An overrider prevents hydraulic pressure being applied to the steering ram until the locks have been withdrawn.
At the front of the semi-trailer a fifth-wheel, rubbing-plate, bolster assembly is carried on 4in. by 4in, box section members. These members can be of any length up to that of the main trailer frame and are not designed to be load-carrying; they will come into operation only when the vehicle is carrying long, self-supporting beams. Should heavy braking be applied, they will prevent long loads sliding off the bolster. The rubbing plate is designed to fold up and form a headboard when the trailer is used as a standard unit and at such times a second rubbing plate and kingpin, permanently fitted in the normal position, come into operation.
That the bogie might be moved, a single landing-leg mounted centrally between the main frames 20ft from the rear of the trailer —in addition to those fitted in the normal position—lifts the frame clear of the kingpin. This can be done only when the vehicle is unladen. When the frame is raised the bogie can easily be rolled backwards or forwards by one man. The whole outfit can, in fact, be operated by a driver working on his own.
Brake hoses and cables used are of the pre-coiled type and, unless the extending fifth-wheel is to be disconnected completely to handle exceptionally long beams, these need no extensions.
The steering ram is disconnected from the main chassis frame when the bogie is set in the forward position. While disconnected, it is clamped to an A-frame on the front of the bogie. Rubery Owen-Rockwell 22,5001b axles and suspension are fitted and the vehicle car be supplied with any one of several sets a. tyre equipment.