Pneumatic trailer braking


The new range of tractors with the 6-cylinder Tier 3 Perkins engine may be fitted with a pneumatic trailer braking system as an option.
There are 2 types of system:
• Double line and single line type
• Double line type
Double line and single line type and comprises 3 couplers located at the rear of the tractor:
• A yellow coupler for the brake line
• A red coupler for the service brake (or emergency brake)
• A black coupler for the single line brake
Double line type has 2 couplers located at the rear of the tractor:
• A yellow coupler for the brake line
• A red coupler for the service brake (or emergency brake)
The brake system control is not completely identical for the Double line type pneumatic trailer braking system. The pneumatic brake systems are identical on tractors equipped with Dyna-6 and Dyna VT transmission. However, the location of the components is different depending on whether the hydraulic system is of the Load Sensing or Open Centre type.

Pneumatic trailer braking components

Compressor:
The compressor is connected to the engine lubrication system. Air sucked in by the compressor is filtered through the engine air filter. The compressor is permanently driven by the engine.

Regulation:
The pressure inside the air tanks is limited by the pressure regulator located on the right-hand side of the tractor. The air pressure is regulated between 6.5 bar and 8 bar. When the pressure is at maximum, the air directed by the compressor leaves the system via the regulator and is discharged into the open air via a silencer. This silencer is fitted on the pressure regulator.
The operating pressure is different depending on the types of pneumatic brake systems :
• Double line and single line type: 7.3 bar
• Double line type: 8.1 bar
The safety valve opens at 12 bar.

Right-hand tank:
The right-hand tank has a capacity of 10 litres. A pressure sensor is fitted to this tank and indicates the pressure of the system.

Left-hand tank:
The left-hand tank has a capacity of 10 litres. This tank is directly connected to the system. The compressor directs the air inside the right-hand tank and then inside the left-hand tank. An automatic bleed system is located underneath the tanks. This allows any water that may still be in the system to drain out.

Electro-pneumatic valve for the Double line type of pneumatic brake system


The valve is controlled by the electrical section of the hydraulic brake system. When the brake pedal is not activated, the electro-pneumatic valve is not supplied and so no pressure is supplied to the pneumatic brake line. As soon as the brake pedal is applied, the valve is supplied (electrically) and pressure is supplied to the pneumatic brake line. The electro-pneumatic valve is supplied at the same time as the brake lights. The electro pneumatic valve reduces the braking response time between the tractor and the trailer.


Main valve for Double line type of pneumatic brake system
This valve is controlled by three different functions:
- By the electro-pneumatic valve
- By the trailer brake oil pressure
- By the parking brake system


Main valve for the double line and single line type of pneumatic brake system
This valve is controlled by three different functions:
- Tractor right-hand brake oil pressure
- Tractor left-hand brake oil pressure
- Parking brake action

Control valve:
This valve, located on the Double line type fitting, is used to control the single line B. It controls the pressure for the black coupler. When the brake is not applied, the pressure is between 4.8 and 5.6 bar, and reduces to 0 bar, reciprocally proportional to the pressure inside the main valve.

Pressure sensor:
The pressure sensor is mounted on the right-hand tank. This sensor measures the pressure of the system and the value is displayed on the DCC2 Dot Matrix screen. If the pressure is less than 4 bar, an indicator light illuminates on the DCC2.

Relief valve:
A relief valve is fitted on the left-hand tank, on the Double line and single line type fitting only. It prevents pressures greater than 9 bar.

Couplers:
Yellow: This coupler connects the trailer's main service brake line.
Red: This line is permanently supplied with compressed air. This coupler must be connected after the yellow coupler and must be disconnected first.
Black: This coupler is only fitted to the German type fitting and is the single line. The couplers are different, depending on country. They are designed in such a way as to prevent incorrect connection.

Operation of the pneumatic system

Double line type

Engine running, brake not activated


Compressor (1): The air compressor sucks in the outside air to compress it. As soon as the engine operates, the compressor is active.
Pressure regulator (2): The pressure regulator maintains a pressure of 6.5 to 8 bar inside the system.
Solenoid valve (6): No action on the brake pedals. The solenoid valve is not supplied. V = 0 Volt. The system's air pressure is unable to control the main valve (7).
Main valve (7): The parking brake is not activated and therefore the air pressure is locked. The brake pedals are not applied, there is no hydraulic pressure over the trailer brake line and so the air pressure remains locked inside this line.
Control valve (8): This valve cannot be controlled while the air pressure remains locked inside the main valve. Therefore, there is no pressure inside the yellow coupler line, but there is air pressure inside the black coupler single line.

Engine running, brake pedals applied


Solenoid valve (6): The brake pedals are fully applied. The solenoid valve is supplied. V = 12 Volt. The system air pressure controls the main valve (7).
Main valve (7): The parking brake is not activated and therefore the air pressure is locked. The brake pedals are applied, the hydraulic pressure over the trailer brake line and the air pressure inside the yellow line controls the control valve.
Control valve (8): The valve is controlled by the air pressure of the main valve. Therefore, there is pressure inside the yellow coupler line, but the air pressure is not available for the black coupler single line.

Engine running, parking brake activated


Solenoid valve (6): The brake pedals are fully released. The solenoid valve is not supplied. V = 0 Volt. The system's air pressure does not control the main valve (7).
Main valve (7): The parking brake is activated. Therefore, the air pressure enters the yellow line and also enters the control valve (8). The brake pedals are fully released, the hydraulic pressure does not enter the trailer brake line and the air pressure remains locked inside this line.
Control valve (8): The valve is controlled by the air pressure of the main valve. Therefore, there is pressure inside the yellow coupler line, but the air pressure is not available for the black coupler single line.

Double line and single line type 

Engine running, brake not activated


Compressor (1): The air compressor sucks in the outside air to compress it. As soon as the engine operates, the compressor is active.
Pressure regulator (2): The pressure regulator maintains a pressure of 6.5 to 7.3 bar inside the system.
Main valve (7): The parking brake is not activated and therefore the air pressure is locked. The brake pedals are not applied, there is no hydraulic pressure over the brake line and so the air pressure remains locked inside this line.

Engine running, brake pedals applied


Main valve (7): The parking brake is not activated and therefore the air pressure is locked. The brake pedals are applied, the hydraulic pressure over the right and left-hand trailer brake lines controls the control valve (7) to supply the yellow line.

Engine running, parking brake activated



Main valve (7): The parking brake is activated. Therefore, the air pressure enters the yellow line, passing via the control valve (8). The brake pedals are fully released. The hydraulic pressure does not enter the
tractor brake lines and the air pressure remains locked inside this line.