What type of brakes do lorries have?

Lorries are equipped with various types of brakes to ensure safe operation, especially given the heavy loads they carry.

Service brakes

Service brakes are the brakes that are activated when the driver pushes the brake pedal. For small trucks, they are the primary braking system, but for larger trucks they are mainly only used in an emergency or when coming to a stop. They are typically hydraulic or air-operated.

• Air brakes: Most lorries in the UK use air brakes due to their reliability and power. When the brake pedal is pressed, compressed air is sent to the brake chambers at each wheel, pushing the brake shoes against the brake drum or disc, slowing the vehicle. Air brakes are advantageous because they can provide the necessary force to stop large vehicles efficiently.
• Hydraulic brakes: Less common on larger lorries, hydraulic brakes use fluid pressure to apply the brakes. They are more common in smaller lorries.

Parking brakes

Parking brakes, also known as handbrakes, are used to keep the vehicle stationary when parked. There is some risk with a cardan shaft handbrake that the driver doesn’t apply enough force, and it can release, causing the lorry to roll away. These are only used on small lorries, and are activated using a lever like a regular mechanical handbrake in a car.

• Mechanical handbrakes: In older or smaller vehicles, you might find a mechanical handbrake that directly engages the brake mechanism on the rear wheels via a cable.
• Spring brakes: These are typically used in conjunction with air brakes. When the parking brake is engaged, air is released from a chamber, allowing a spring to push the brake shoes against the drum or disc, holding the vehicle in place. This system is failsafe because it relies on spring tension rather than air pressure to stay engaged.

Retarder brakes

Retarder brakes are auxiliary braking systems designed to assist the service brakes, particularly on long descents where continuous braking is required.

• Exhaust brakes: Commonly found on diesel engines, exhaust brakes work by restricting the engine’s exhaust flow, creating back pressure that slows the engine and, in turn, the vehicle.
• Engine brakes (‘Jake Brakes’): Often used on heavy lorries, these work by altering the timing of the exhaust valve openings, effectively turning the engine into a compressor and providing substantial braking force.
• Electric retarders: These are mounted on the drive shaft and work by generating electromagnetic resistance, slowing down the vehicle.

Trailer brakes

When towing a trailer, it’s crucial that the trailer has its own braking system, which works in tandem with the lorry’s brakes.

• Air-operated trailer brakes: These are the most common on heavy trailers. The lorry’s air braking system is extended to the trailer via air lines. When the driver applies the brakes, air pressure is sent to the trailer’s brake chambers, operating the brakes just like on the lorry.
• Electric trailer brakes: More common in smaller trailers, these brakes are controlled by an electric signal from the lorry. The driver can usually adjust the braking force via a control box in the cab.
• Breakaway brakes: This is a safety feature on trailers where, if the trailer becomes disconnected from the lorry, the breakaway cable pulls tight, activating the trailer’s brakes to bring it to a stop.

5. Anti-lock braking system (ABS)

ABS is a crucial safety feature that prevents the wheels from locking up during hard braking, helping maintain control of the vehicle. In the UK, ABS is required on most lorries and trailers. It works by rapidly pulsing the brakes when the system detects a lockup, allowing the driver to maintain steering control.

6. Electronic braking systems (EBS)

EBS is an advanced system that electronically controls the braking force at each wheel for optimal braking performance. This system can integrate with ABS and other safety features, providing more efficient and responsive braking. Trailer EBS is particularly useful in preventing rollover accidents.

These braking systems work together to ensure the lorry and its trailer can stop safely, even under heavy loads or in emergency situations. Understanding and maintaining these systems is crucial for safe lorry operation.