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13 May 2019

Tractor hydraulic braking system for trailers


How does the SDF double output trailer hydraulic engine brake affect the trailer?

The output of the SDF is established in the Delegated Regulation (EU) 2015/68. (OJ dated 23/01/2015) in Section 2.1.5:•    Hydraulic hose coupling, pursuant to standard ISO 5676:1983 (male connector on the tractor and the female connector on the trailer)•    Extra hydraulic hose, according to the standard ISO 16028:2006 size 10 (male connector on the tractor and female connector on the vehicle being towed).Moreover, it establishes that the trailer begins to brake before the tractor.

The regulation 2015/68 takes into consideration the differences between tractors whose maximum speed is equal to or less than 40 km/h and those that are faster than this. In the first case SDF has the "Ta" brake option; and the "Tb" option for the second case.

For the Ta option there is a hydraulic logic valve for the trailer braking system. When the motor is running, the hydraulic inlet supplies pressure for the hydraulic braking system (0 to 150 bar) through the control line hose (ISO 5676). It is the pressure needed for the brakes to work and it is the general solution.When the solenoid valve is connected, the hydraulic inlet of the extra control line hose (ISO 16028) supplies pressure of between 15 and 35 bar to operate the brakes (On/Off of the solenoid valve).

With regard to the Tb option (tractor with trailer at more than 40 km/h) it operates the proportional PSV valve with a pressure of 3.5-17.8 bar, plus what the hydraulic system supplies (up to 150 bar). In this case the tractor needs to be fitted with a valve for the parking brake and a sensor for the gradual control of the secondary braking system (Connector ISO 7638:2003 with five or seven pins).Consequently, seeing as the maximum speed limit for tractors with trailers in Spain is 25 km/h, the inlet ISO 5676 is recommended. The output (pressure) in the extra inlet is controlled by Logic Solenoid Valves with different configurations to adapt to the demand of different countries.

For more information about everything related to the braking system of tractors and trailers read the Delegated Regulation (EU) 2015/68, which is really complex.

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