Striking Features in a New Semi trailer
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Advanced Frame Design, Novel Hydraulic Lifting Gear and a Special Braking System are Features of the New Hands Semi-trailer
nESIGNED for 5-6-ton pay-loads, an interesting new
semi-trailer outfit has been placed on the market by Hands (Letchworth), Ltd., of Letchworth. Two forms are available, the standard-model, which has a single axle, and a further model having a double-bogie axle. At the same time the frame may be of the straight, semi-drop or full-drop type and the variance in the loading heights of the drop-frame models may be set to any reasonable dimension to cater for special operating conditions.
The frame design is of particular interest, in that the method of construction employed enables a large saving in weight to be obtained without any loss of strength or rigidity. As will be seen from accompanying illustrations, a central box girder of great strength forms the backbone of the frame. The cross-members are pressed from the same material and are electrically welded to the main girders.
Light side-members are welded to the cross-members, and these embody a profile border which protects the flooring and carries the body brackets and hinges. A feature of interest is that the flooring is fixed into the profile border so that there is no need for outrigger brackets, body runners or a ,sub-frame. , Incorporated in the head of the main frame is the housing for the hydraulic lifting gear. This two-speed gear is of ingenious design and, in addition to fulfilling its primary function of lifting the trailer clear of th'e tractor, it automatically controls the coupling gear and the braking system. The control lever, mounted on a quadrant in the driver's cab, has three positions—" closed," " pump " and "open —and to uncouple the trailer the lever is moved from the " closed" to the " pump " position. This operation releases the locking sleeve on the turntable and allows the high gearing of the hydraulic pump to be brought into action.
The pump is then operated by means of a lever on the near side of the vehicle and the jockey wheels are lowered. So soon as the wheels are on the ground, low gear may be engaged and the actual lifting of the trailer from the tractor is effected. When the trailer is lifted clear of the turntable the rear brakes are automatically applied and the rearlight adapter is disconnected.
Re-coupling may be effected from any angle, and during this, operation the locking sleeve is masked by the turntable housing and cannot be subjected to any impact, 'in the event of the trailer being carelessly driven. When the trailer is in position, the control lever is moved to the " closed " point, and this operates the locking sleeve, brings the brakes under control from the tractor, remakes the rear-light connection and returns the hydraulic lifting gear to the " off " position.
The range of lift provided is ample, and the control is so arranged that the trailer may be dropped inch by inch to mate with the turntable should the tractor wheels sink into soft ground, or should any alteration in levels have
taken place due to the attachment having been moved from the place where it was uncolipled.
Of particularly sturdy construction, the turntable is mounted on large silentbloc bearings and the king-pin has a diameter of 4T36. ins.
Low-periodicity semi-elliptic springs are employed at sess be rear of the trailer, and a point of interest is that they are provided with fixed anchorage points, no shackles being used. The movement caused. by spring deflection is transmitted through the main leaves, the ends of which are forged to form spring eyes. The spring bosses are of large diameter and are fitted with phosphor-bronze bushes.
In the case of the double-bogie niachine a similar method is adopted, but the springs are transversely mounted, the axle bearers being carried on large bearings fitted in the spring bosses. Accompanying illustrations clearly show the springing systems on the two models.
Brakes operated by air pressure or by vacuum may be used the standard trailer illustrated being equipped with brakes of the vacuum type. In this system a vacuum tank is mounted behind the driver's cab, and the braking effort is derived from compression springs of predetermined strength, which are incorporated in the brake cylinders. The desired braking force is obtained by controlling the pressure exerted by these springs. This control is obtained by a regulating valve, which not only maintains a constant balance of vacuum throughout the system, but sets the time of the braking effort to give an early or delayed action in relation to the braking of the tractor unit.
The trailer brakes are independently connected to the foot and hand brakes of the tractor unit, and a further point is that a mechanical control is provided to operate the trailer brakes when required.
When the semi-trailer is uncoupled from the motive unit the vacuum line is automatically disconnected through the medium of a patented valve and the trailer brakes are immediately applied. In the case of the air-pressure system, the method of brake operation is similar to that described.
Accompanying illustrations show the method of construction adopted for the double-bogie type, and it will be noted that the brake-operating gear is atcommodated within the axle bearer. To enable the tyres of the inner wheels to be changed, or to inspect the brakes or hubs, the axle bearers can be revolved upon their own axes so that the inside wheels can be brought to the outside positions.
Space precludes a detailed description of the hydraulic pump gear and the patented control valves, but we noted that all parts of the gear are substantially built.
At a demonstration we witnessed at the maker's works, we were impressed with the ease and certainty of the control; the trailer was easily lifted and uncoupled in under half a minute, and re-coupling presented no difficulties. The trailer illustrated weighs under 3 tons unladen and we understand that the price is to be competitive,