14 Trailer and caravan drawbar couplings

1.4.1 Eye and bolt drawbar coupling for heavy goods trailers (Figs l.25 and l.26) Drawbar trailers are normally hitched to the truck by means of an 'A' frame drawbar which is coupled by means of a towing eye formed on the end of the drawbar (Fig. l.25). When coupled, the towing eye hole is aligned with the vertical holes in the upper and lower jaws of the truck coupling and an eye bolt passes through both coupling jaws and drawbar eye to complete the attachment (Fig. l.26). Lateral drawbar swing is permitted owing to the eye bolt pivoting action and the slots between the

|t>) Front sectional view of fifth wheel coupling assembly

Fig. 1.22(a and b) Fifth wheel coupling assembly

|t>) Front sectional view of fifth wheel coupling assembly

Fig. 1.22(a and b) Fifth wheel coupling assembly jaws on either side. Aligning the towing eye to the jaws is made easier by the converging upper and lower lips of the jaws which guide the towing eye as the truck is reversed and the jaws approach the drawbar. Isolating the coupling jaws from the truck draw beam are two rubber blocks which act as a damping media between the towing vehicle and trailer. These rubber blocks also permit additional deflection of the coupling jaw shaft relative to the draw beam under rough abnormal operating conditions, thus preventing over-straining the drawbar and chassis system.

Fig. 1.23(a-d) Fifth wheel coupling with twin jaws plunger and pawl
Fig. 1.24(a-d) Fifth wheel coupling with single jaw and pawl

Hinge pin i Turntable

Hinge pin i Turntable

Towing eye

Fig. 1.25 Drawbar trailer

Towing eye

Fig. 1.25 Drawbar trailer

The coupling jaws, eye bolt and towing eye are generally made from forged manganese steel with induction hardened pressure areas to increase the wear resistance.

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