Suspension systems are almost as old as vehicles themselves. But, as with other aspects of vehicle design, they’ve undergone numerous changes, the most recent being a shift from passive to active systems.
A single vehicle may have multiple suspension systems, typically including a primary suspension system, which absorbs inputs from the axles, along with seat and cab suspension systems. Each system is expected to accommodate different frequency inputs, with the end goal of providing the best overall ride experience for the operator and cargo under the majority of driving conditions.
Traditional passive spring and damper systems react to load inputs from a vehicle’s wheels and body. They exhibit relatively constant spring rates and damping forces regardless of the road and load conditions. In contrast, adaptive, or semi-active suspensions, use an onboard system to control spring and damper movement and continuously alter their settings in real time to suit different load conditions, providing improved dynamic stability and comfort.
Vibration loading can be particularly problematic for cabs on heavy equipment—so problematic, in fact, that many governments are requiring OEMs to protect operators from the harmful effects of whole-body vibration. Choosing a cab suspension system that offers maximum protection under such harsh operating conditions, therefore, is vital.
What’s Inside a Cab Suspension System
Traditional cab suspension systems typically compromise between ride comfort and stability, but systems that integrate the air spring, damper, controls, sensors and leveling valves offer a more regulated system.
- The air spring provides a soft suspension for low-frequency vibrations.
- The damper is used only when needed to provide stability and shock protection.
- The leveling valves help keep the cab level during operation to provide optimal suspension performance during most driving conditions.
A Better Damper Makes A Better System
LORD suspension systems use our proprietary magneto-rheological (MR) fluid, which contains magnetic (typically iron) particles. In the presence of a magnetic field, the particles link and quickly change the fluid to a semi-solid. When the magnetic field is removed, the fluid just as quickly reverts back to its natural free-flowing state.
An MR damper contains chambers between which MR fluid moves, converting “shock” energy into heat. Similar in principle to passive hydraulic dampers, an MR damper differs in that an electrical circuit is introduced in the piston assembly, creating a magnetic field that alters the state of the MR fluid. The resistance of the damper, therefore, can be continuously changed in real time by modulating electrical current to the damper.
Control systems that leverage a network of sensors, which continuously monitor the driving situation in a vehicle, deliver this precise control of the damper. Our proprietary “skyhook” and “endstop” control algorithms use data from the vehicle's sensors to adjust the damping force to the optimum level within milliseconds.
With semi-active cab suspension systems, OEMs no longer have to choose between achieving a low-vibration environment and maintaining vehicle stability. Customized controllable damping significantly improves vehicle ride comfort as well as handling and safety.