How Haldex trailer suspension systems work
With features such as height control, raise and lower, reset-to-ride, second ride height and lift axle control, Haldex suspension systems offer trailer users a valuable set of options in a modular system.
Here is how they work.
Haldex offers air (pneumatic) trailer suspension systems that complement its range of brakes. Air suspensions guarantee a standard ride height by transferring all of the variations between a full consignment and empty load as a difference in pressure within the trailer’s air bags (normally one is fitted per wheel end).
Mechanical suspensions consist of leaf springs whose mechanical deflection under load helps cushion the trailer from the worst of the bumps on the road. The deflection is proportional to load, and it is easy to see how much weight is on the vehicles by the closeness of the body to the axles. Mechanical suspensions are now restricted to a minority of the market, primarily construction vehicles.
By comparison, air suspensions offer a much greater cushioning effect, leading to greater riding comfort, more stable driving and cornering characteristics, plus the possibility of extra features.
The Haldex single-circuit air suspension system links air bags in all of the axles in the circuit in parallel, not in series. The simplest system feeds all trailer axles in a single circuit from an air tank, supplied via a pressure protection valve by the service brake circuit. A more common architecture is a dual-circuit system, each one linking wheel ends on one side of the vehicle. In either case, the system automatically compensates for load imbalances across or along the trailer bed through the flow of air, which naturally works to equalise pressure through a levelling valve.
For increased trailer stability, restricted airflow is required in the air suspension when turning at high speeds. Under these conditions, centrifugal forces tend to increase suspension air pressures in the side of the vehicle on the outer radius of the turn, which could destabilise the trailer. To minimise this natural effect, Haldex’s dual-circuit height control system has included a cross-flow limiter.
An integral part of many trailer suspension circuits is a raise and lower valve, which allows the height of a trailer bed to be manually adjusted by turning a lever; Haldex’s system is called COLAS+. It works with both single and dual-circuit suspension systems, fed in series from a levelling valve. Mainly used to adjust the trailer deck height to fit a loading dock, it is also used to lower the trailer on ferry journeys to minimise trailer sway. Users turn the handle anticlockwise to raise, and clockwise to lower. Inside, a piston raised or lowered by an extender is attached to the handle. Turning the handle to the right, and pushing it again, locks it in the down position.
COLAS+ offers two safety functions. First, a dead-man control, a safety feature to protect a worker underneath the trailer, means that actuation stops as soon as the handle is released; the spring-loaded handle automatically returns to neutral position. Second, setting off on the road before restoring the correct riding height could damage the air bags (if the bed is too low) or risk a collision with a low-clearance bridge, or pose other potential problems. To prevent this, an optional reset-to-ride function, first invented by Haldex more than 20 years ago, automatically returns the bed to the correct ride height, using a signal sent to an actuator solenoid. This feature automatically releases the COLAS+ handle when in the locked-down position. COLAS+ can also incorporate an ISO3585 test point in the handle assembly, rather than having to venture underneath the trailer to attach diagnostic tool leads.
Speaking of inventions, more than 25 years have passed since Haldex first launched a lift axle system, which raises or lowers an individual axle with air pressure. It is still called ILAS (Integrated lift axle system). Raising an axle can save tyre wear and fuel when travelling empty.
Such an arrangement limits the amount of lifting of a lift axle. In cases where greater height is required, Haldex offers another variant of a levelling valve with a second port that provides a second, higher, ride height. This raises the entire chassis – including the lift axle – for greater clearance.
The latest version, ILAS E+, is controlled with a load-dependent signal from EBS systems and offers a very simple installation.
Haldex modular suspension systems provide a diverse feature set to support the safe and efficient transport of goods for operators with simple or complex needs.
