Achieving product differentiation without adding significant cost is on the wish list of all automakers. While targets can be reached to some degree by applying clever software changes to sophisticated systems, using purely mechanical solutions as an alternative to those systems may be difficult, particularly in that subjective area categorized as “refinement.”
Ride refinement is a prime example. China-based chassis systems’ supplier BWI Group produces the sophisticated magneto-rheological suspension control, MagneRide, used by a growing list of brands including Audi, Cadillac, Chevrolet (Silverado pickups and Corvettes) and Ferrari. But BWI is also developing what it believes will be a cost-effective system aimed at raising the ride quality of mid-class premium cars.
Enter the HCS
It is doing so by focusing its R&D on the conventional bump stop as a route to improving ride comfort without degrading vehicle handling and safety. BWI engineers plan to extend the performance of conventional passive dampers by replacing hard bump stops with an hydraulic compression stop (HCS) integrated into the damper.
“At the top end of the market, adaptive suspension technology such as MagneRide virtually eliminates the compromise between ride comfort and body control,” explains Roman Bielak, BWI Group’s Technology Development Manager. “The challenge with passive dampers is to retain the price advantage while closing the performance gap to adaptive systems. HCS is an important step towards this.”
It is designed to better optimize damping over the full amplitude of wheel travel to secure improved road isolation: “The new system is not only more tunable than traditional bump stops, leading to better vehicle dynamic performance, but improves NVH by reducing peak forces transmitted to the vehicle body at the limit of travel,” Bielak told Automotive Engineering.
Thinking behind the HCS, due to enter production in 2018, is to soften the load spikes that normally occur at the limit of compression. This would allow chassis designers to make greater use of the available damper travel to improve occupant comfort and chassis refinement. It would also complement and facilitate reduced weight of a vehicle’s body without affecting ride quality or handling, because the strength and stiffness requirements of body structure at the tower would be lower for the same standard of refinement and durability.
“A heavily laden vehicle that is more likely to bottom its suspension on bumpy roads can do so without transmitting damaging loads into the body structure,” says Bielak.
The HCS, now being demonstrated to OEMs, is a development of BWI Group’s established hydraulic rebound stop (HRS) technology, which has been re-optimized for use in compression rather than rebound. Capability of both HRS and HCS is to reduce the shocks transmitted to the vehicle body at the limits of suspension travel by dissipating the energy hydraulically in the damper fluid.
HCS is being developed in two configurations to suit applications requiring either high or low damping levels. The high level is achieved by adding a sealed hydraulic chamber with a by-pass to the damper’s existing compression valve. The separate chamber allows very high damping forces to be generated without influencing damping over the remainder of the suspension travel.
For applications requiring lower levels of damping, BWI Group uses a damper tube swaged to give two diameters. The larger diameter is the main damper valve, the smaller engages a second valve at the chosen threshold of travel, before the limiting stroke is reached.
Hybrid and EV opportunities
Bielak explains this design gives greater opportunity for damper tuning. But he explained that the maximum damping force must be limited so that oil aeration does not degrade the base damper performance.
"We are developing two HCS technologies because different vehicle applications each have specific priorities," he noted. "Both approaches improve the comfort, refinement and durability of the vehicle but one offers greater potential for fine tuning while the other provides higher levels of damping.”
He added that although aimed initially at mid-range premium passenger cars, he believes that HCS could be particularly helpful when applied to hybrid or electric vehicles derived from existing models, because it avoids any major suspension changes. “The technology copes well with the additional weight of a large battery pack," he said, "and satisfies the lower cabin noise levels required when driving in electric mode by ensuring equally low levels of transmitted noise from the suspension.”
Potential customers (at present not named by BWI Group) for the system are currently evaluating the low-damping variant of HCS, which has been confirmed for production in 2018.