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Trailer Assist

Some trailers, pulled by farm tractors and heavily loaded, are used for intensive work on ground with very variable surface grip conditions. This mainly applies to forestry trailers, dump trucks used for excavation work, or agricultural pulled behind sprayers used on hilly fields.


Under these conditions, the use of bigger and more powerful tractors does not help to solve the problem, with the tractive effort being limited by the grip of the machine’s tires and the load applied to each of its axles. It is the weather that determines what work is to be carried out, with financial consequences and delays on the work site being at stake. 
So, herein lies the problem. One solution consists in adding to the trailer a drive system that uses hydrostatic
transmission. This addition to the tractive effort is activated at the request of the driver and is available for speeds up to 15kph; above this, the system automatically disengages. The mechanical losses linked to the system are therefore minimal when driving on roads at the maximum authorized speed of 40 kph.
Furthermore, when the system is in gear, the «engine brake» effect generated by the hydrostatic transmission helps to retain the tractor when moving downhill. This automatic deceleration prevents the driver from operating the friction brakes. The convoy’s safety is optimal.
Poclain’s Trailer Assist solution consists of:

  • a PM50 closed loop hydraulic pump driven by the tractor’s mechanical or hydraulic power take-off.

  • two MSE18 «low speed high torque» high-efficiency hydraulic motors installed in one of the trailer’s axles, with free-wheeling capability.

  • a hydraulic valve controlling the power to the two motors depending on the needs and speed of the convoy.

  • a relay box or SD-CT30 control unit (for the «electronic management» option) providing management of the system using data from the hydraulic motors, the service brake

  • control and the oil temperature. 

Through its architecture, the system is completely independent from the tractor’s hydraulics. Hence, the trailer’s drive system performances are guaranteed whatever the characteristics of the towing vehicle used.

The closed loop pump fitted to the trailer and used in place of the tractor’s hydraulics, helps to provide a maximum pressure of 400 bars in the system as well as the «engine brake» retaining effect. The high pressure hydraulic motors may then be used to their full torque potential. One single drive axle is sufficient, whereas the use of the tractor hydraulics, limited to 250 bars, would require two drive axles. Finally, there is no possible risk of oil pollution (no risk to mix tractor oil with closed loop trailer oil), since the only connection between the tractor and trailer is the mechanical or hydraulic power take-off.

The Trailer Assist systems’offer is two-tiered:

  • Trailer Assist «Entry» for the occasional need for help and easy set-up on the trailer.

  • Trailer Assist «Medium» for intensive use of the system and for making the best possible use of the transmission options via electronics.

The Poclain Trailer Assist system in its «Medium» version is currently fitted to the Hardi-Evrard’s pulled behind Meteor 6x6 sprayer as well as to the DTP-21 public works tipper from the French manufacturer Delaplace.

Source: Poclain Hydraulics, Ltd.