Tractors are equipped with a fifth-wheel coupling device with a locking opening in the jaws of 50.8 mm in diameter. The device is designed for the articulated connection of the tractor with a semi-trailer having a standard coupling pin.
The fifth wheel 10 (Fig. 1), on which the semi-trailer rests, rocks in the longitudinal and transverse planes. In the longitudinal plane — on the axles 15, in the transverse plane — due to the deformation of the rubber of the hinges 11.
The coupling of the fifth wheel with the semi-trailer pin is accomplished by two jaws 2 of the coupling mechanism.
The jaws are mounted on pins 14 and, rotating on them, embrace the pin.
The jaws are held in the closed position by the locking wedge 3 under the action of spring 5 mounted on the locking wedge rod.
When coupling has occurred, the unintentional uncoupling prevention device 4 assumes a vertical position.
To uncouple, turn the unintentional uncoupling prevention device aside and use handle 1 to move the locking wedge 3 to the extreme forward position.
The pawl 6, pulled by spring 7, locks the wedge in the forward position.
When the tractor moves away, the semi-trailer pin spreads the coupling mechanism jaws and disengages from them.
The left jaw, using a pin on it, rotates the pawl, which allows the locking wedge to move back until it contacts the ends of the jaws, which are held in the open position.
With this position of the mechanisms, the fifth wheel is prepared for automatic coupling with the semi-trailer.
During coupling, the semi-trailer pin, as it moves, rotates the jaws and forces them to close.
The locking wedge, sliding along the ends, enters the groove of the jaws, closing them automatically.
The fifth-wheel coupling device is attached to the tractor frame through brackets 13, the subframe and cross members. To facilitate coupling of the tractor with the semi-trailer, loading ramps are installed behind the fifth-wheel device.
Coupling and uncoupling
Before coupling, make sure that the fifth-wheel device and its attachment are in good condition, the fifth wheel and ramp guides are not dirty and there are no foreign objects on them; if necessary, clean the upper surface of the fifth wheel from contaminated lubricant and lubricate with a thin layer of fresh lubricant.
Securely brake the semi-trailer with the parking brake and place it on its support device so that the support surface of the semi-trailer is at the same level as the tractor fifth wheel or slightly below it.
Perform coupling and uncoupling on a level horizontal area with a hard surface.
The longitudinal axes of the tractor and semi-trailer must be in one straight line.
Coupling procedure:
- 1. Move the unintentional uncoupling prevention device aside and set the jaw lock handle to the extreme forward position.
- 2. Reverse the tractor slowly towards the semi-trailer so that the semi-trailer pin enters between the ramp guides and enters the fifth wheel jaws until it stops. The coupling should then occur automatically.
- 3. Brake the tractor with the parking brake.
- 4. Ensure that the jaw lock handle is in the extreme rear position and that the unintentional uncoupling prevention device is lowered vertically downwards and locks the locking wedge rod.
- 5. Raise the semi-trailer support device to the extreme upper position and secure it firmly.
- 6. Connect the semi-trailer electrical wiring connecting cable to the socket.
- 7. Connect the connecting hose of the tractor pneumatic brake actuator to the semi-trailer coupling head.
- 8. Open the valves of the pneumatic brake actuator on the tractor and semi-trailer by placing their handles parallel to the longitudinal axis of the valve.
- 9. Release the semi-trailer parking brake.
- 10. Move the road train forward some distance, ensure that the coupling is in good condition, the brakes and electrical devices of the semi-trailer are working properly.
Uncoupling procedure:
- 1. Brake the semi-trailer with the parking brake.
- 2. Lower the semi-trailer support device until it contacts the road surface, slightly unloading the tractor springs.
If forced uncoupling on unconsolidated ground is necessary, place pads under the semi-trailer support device.
- 3. Close the isolating valve of the tractor pneumatic system and the semi-trailer brake control valve by placing their handles perpendicular to the longitudinal axis of the valve.
- Disconnect the coupling heads of the pneumatic brake actuator and close the protective caps of the heads.
Secure the coupling head with the hose on the tractor platform.
- 4. Remove the plug of the electrical wiring connecting cable from the socket and secure the cable on the tractor platform.
- 5. Move the fifth wheel unintentional uncoupling prevention device aside and move the jaw lock handle to the extreme forward position.
- 6. Engage first gear and slowly move the tractor forward until it is completely uncoupled from the semi-trailer.
When installing the fifth-wheel device on the vehicle, before tightening the bolts and clamps, it is necessary to use adjusting shims to ensure a gap of 2–3 mm between the frame brackets and the subframe.
The tightening torque of the fifth-wheel device attachment should be 10–14 kgf·m, for M14 bolts – 8–10 kgf·m.
