Drawbar (haulage)

A drawbar is a solid coupling between a hauling vehicle and its hauled load. Drawbars are in common use with rail transport, road trailers, both large and small, industrial and recreational, and with agricultural equipment.

A large ballast tractor pulling a load using a drawbar
General duty tow hitch from VBG on a truck and a drawbar on a trailer

Agriculture and horse-drawn vehiclesEdit

Agricultural equipment is hauled by a tractor mounted drawbar. Specialist agricultural tools such as ploughs are attached to specialist drawbars which have functions in addition to transmitting tractive force. This was partly made redundant with Ferguson’s development of the 3 point linkage in his famous TE20. A wooden drawbar extends from the front of a wagon, cart, chariot or other horse-drawn vehicles to between the horses. A steel drawbar attaches a three-point hitch or other farm implement to a tractor.

RoadEdit

A drawbar is a towing or pushing connection between a tractive vehicle and its load.

Light vehiclesEdit

On light vehicles, the most common coupling is an A-frame drawbar coupled to a 1 7/8 inch or 50mm tow ball. These drawbars transmit around 10% of the gross trailer weight through the coupling.

Heavy vehiclesEdit

The direction of haulage may be push or pull, though pushing tends to be for a pair of ballast tractors working one pulling and the other pushing an exceptional load on a specialist trailer. The most common drawbar configuration for heavy vehicles is an A-frame drawbar at the front of a full trailer that connects to a tow coupling on a hauling vehicle[1]

On heavy vehicles, the drawbar is coupled using a towing eye, typically of 40mm or 50mm diameter, connected to a bolt and pin coupling. Commonly seen brands include Ringfeder, V. Orlandi and Jost Rockinger. These drawbars transmit little or no downwards force through the coupling.

The drawbar should not be confused with the fifth wheel coupling. The drawbar requires a trailer which either loads the drawbar lightly (for example a small boat trailer, or caravan, or the load is the weight of the coupling components only (larger trailers, usually but not always with a steerable hauled axle, front or rear). By contrast, the fifth wheel is designed to transmit a proportion of the load's weight to the hauling vehicle.

RailEdit

Two or more passenger or freight cars may be attached by means of a drawbar. At both extremes there is a regular coupler such as the North American Janney coupler or the Russian SA3 coupler. This drawbar eliminates slack action.

Rail applicationsEdit

See alsoEdit

ReferencesEdit

  1. ^ "What is a drawbar trailer".
  • US 6739402  Transport drawbar
  • US 5096075  Slackless drawbar assembly with gravity responsive wedge (rail application)
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