“Drivers don’t want to accept a trade-off between better handling and comfort, and not all are prepared to invest in an adaptive suspension system,” said Slawomir Dzierzek, BWI Group’s Damper Module Engineering Manager, based at the company’s Krakow, Poland, Technical Center.
“Because of this, we see real opportunities for passive suspension to make significant further advances that can reduce the performance gap with adaptive systems. By improving each of the key areas that limit the damping performance of a passive system, such as the rebound stop, we will produce a better overall result,” he added.
Applications include SUVs, D-segment (large) cars, and armored versions of regular vehicles used for VIP security, the increased weight of which places additional demands on the dampers.
The chassis and braking system specialist company, which acquired the business of Delphi Chassis Systems in 2009, has designed what it describes as a new, more tunable, internal hydraulic rebound stop that allows chassis engineers to use the damper extension stroke more effectively.
The technology is part of the company’s strategy to reduce the compromise between ride and handling by improving passive dampers and offers an alternative to the typically used deformed tube and flexible rubber parts, with a molded plastic sleeve, elastic ring, and piston.
The work complements BWI’s development of adaptive suspension systems to reconcile the conflicting requirements of ride comfort and handling precision, because the company is confident that there remains considerable scope for improvements in passive technology. BWI states that its advances in passive damper valve technology demonstrates an ability to produce damping curves similar to those achieved with adaptive systems.
Hydraulic rebound stops use hydraulic fluid to dissipate energy when the damper approaches its full extension. The technology can reduce the peak force by two to three times compared to a traditional mechanical rebound stop, producing a smoother ride and preventing damage to the vehicle or suspension, explained Dzierzek.
“With a growing number of vehicles using softer suspension settings to provide improved ride comfort, rebound and bump stop performance has an increasing influence on both NVH and durability,” he said. “But this cannot be achieved at the expense of body control. The hydraulic rebound stop allows more effective use of the entire damper stroke and provides superior control of deceleration at the end of the stroke.”
BWI’s rebound stop incorporates bypass slots that allow modification of its damping characteristic, providing higher levels of damper control. The bypass slots in the sleeve and the use of a self-sealing ring allow BWI to increase the damping force at the end of the piston stroke even when the rod speed is decreasing.
The system deactivates when the stroke reverses, allowing immediate buildup of compression damping forces.
“The plastic sleeve provides high levels of geometric accuracy for precise tuning,” added Dzierzek. “The switching point, when the additional hydraulic load appears, can be adjusted to suit different vehicles and suspension configurations. The level of damping force and the rate at which it increases can also be modified to provide optimum ride comfort for each application.”
BWI’s work on valve design to extend the performance range of passive dampers also includes a “super-progressive valve” for the compression stroke. The smarter valves in the company’s dampers produce curves that allow the suspension to react differently to inputs of various amplitudes and speeds. The action reduces the severity of any shocks transmitted through the rubber mounts to the vehicle body and occupants.
The new internal hydraulic rebound stop has been designed to simplify the component’s assembly and to integrate into standard dampers.
BWI states that the first application will be on an armored vehicle to counter the effects of added weight on its dampers.