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 agricultural equipment.

Agriculture and horse-drawn vehicles

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 three-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.

Road

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

Light vehicles

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

Heavy vehicles

The direction of haulage may be push or pull, though pushing tends to be for a pair of ballast tractors working together, 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 drawbar eye, typically of 40 mm or 50 mm 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. Drawbar configuration is mostly seen on hydraulic modular trailer and ballast tractor combination to haul oversize loads which require special trailer and tractor.

Drawbar eye

A drawbar eye, also called tow eye, is a mechanical part to connect an independent trailer/dolly via a drawbar coupling to a tractor.^[2] the eye is connected to the front end of a drawbar with bolt, flange-mounting or welding.^[3] Most are made from high tension material to bear heavy loads while being pulled by the tractor. The eye is made in the shape of an "i" with a hole at top which is locked in the drawbar coupling and the lower part is mounted to the drawbar making it an essential connector between the drawbar and drawbar coupling. The drawbar eye is used in many heavy transport operations around the world. It is mostly used for agriculture equipment, construction equipment, road trains, dolly trailers, full trailer and hydraulic modular trailers.

Rail

Two or more passenger or freight cars may be attached by means of a drawbar rather than a coupler. At each end of the permanently coupled vehicles there is a regular coupler, such as the North American Janney coupler or the Russian SA3 coupler. The use of a drawbar eliminates slack action.

Rail applications

References

^ "What is a drawbar trailer". 19 July 2021.
^ "Drawbar Eye Definition". Law Insider. Retrieved 2022-03-14.
^ "Drawbar eyes". VBG. Retrieved 2022-03-14.

External links

US 6739402 Transport drawbar
US 5096075 Slackless drawbar assembly with gravity responsive wedge (rail application)
US 5598937 Slackless drawbar assembly (rail application)

[1] "What is a drawbar trailer". 19 July 2021.

[2] "Drawbar Eye Definition". Law Insider. Retrieved 2022-03-14.

[3] "Drawbar eyes". VBG. Retrieved 2022-03-14.

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