After a decade of only partially fulfilled promises, global platforms are finally demonstrating their true value. With similar vehicles now built in Europe, Asia, the USA and Russia, opportunities for cost saving and avoiding the proliferation of parallel specifications have never been greater.
As OEMs turn increasingly to global platform strategies, they walk a tightrope between two conflicting challenges: too great a commonality of components compromises the individuality and competitiveness of the individual regional models; too little commonality undermines the goal of platform sharing, as multiple specifications increase the parts count and reduce economies of scale.
This is perfectly illustrated by the dilemma facing chassis engineers. The drive towards global platforms has shifted the emphasis of damper development beyond improving specific damper performance to developing sufficient dynamic range, so that chassis engineers have the elbow room to meet global requirements with common hardware. “We are giving the vehicle engineers a bigger sand pit in which to play,” says Olivier Raynauld, Manager of Global Technology and Business Development at BWI Group, the Tier 1 suspension and braking system supplier.
The ‘sand pit’ Raynauld refers to is the system operating envelope, which must be big enough to satisfy different regional preferences and road conditions. “A system with insufficient bandwidth effectively ‘locks up’ at higher frequencies, meaning the control of wheel-hop motion is no better than with a passive damper,” explains Raynauld. “The challenge for any controlled suspension is therefore to minimise the time spent operating as a passive system; the lower the available bandwidth, the earlier the point at which the system must rely on its passive characteristics, making wheel control and ride comfort harder to achieve. This explains why there are fundamental differences between the on-paper performance of some systems and their capabilities in practice.”
Stable tyre forces are essential for predictable vehicle handling and improved safety: their effective management requires control of wheel-hop frequencies around 10-15Hz. Ride comfort depends on good body control when subjected to road features, typically involving frequencies in the range of1-2Hz. Disturbance from the wheels must be minimised – this is the basic requirement of effective Skyhook semi-active damping control – so the wheel frequencies really should be actively controlled. And that, in turn, dictates the required bandwidth of a successful system.
Equally important is the response time of the system: if too long, the appropriate damping force is not provided when required. The response speed, from firm-to-soft and soft-to-firm, must be short enough to ensure the selected damping coefficient is kept in the correct phasing in order to provide the required damping at all times. “It is important to achieve times below 20ms for the soft-firm, firm-soft damper transitions, combined with the necessary bandwidth to separate body control and wheel control effectively,” says Raynauld.
“The key to greater hardware commonality, across different regions and markets, and between different models, is to eliminate the need to change the passive hydraulic damping,” Raynauld continues. “Once this point is reached, all the differences can be accommodated through fine tuning by wire, enabling the OEM to accommodate the variations in road types and surfaces that occur in different markets without introducing regional variations in damper hardware.
“One OEM, for example, produces an exclusive, long wheelbase variant for China, which required a recalibration of the software, while the hydraulic damper hardware remained the same” he says. “With shared platforms, the calibration is often changed between models such as the Audi A3 TDI and TT RS, but all the hardware remains common.”
The use of regional assembly plants, building products in parallel and supported by local supplier networks, further complicates the picture. “In order to ensure uniformity of hardware performance between regions, common specifications alone are not enough; global quality standards for every manufacturing step must be maintained,” says Raynauld. “In this respect, the role of quality and manufacturing engineers can be as crucial as that of the original development team.”
In a global market, where product differentiation is often paramount in achieving and retaining market share, controlled or semi-active suspension systems can help by delivering ride and handling performance that is optimised for each market, and on every model variant, while minimising expensive hardware proliferation. Aligning with recent trends and public expectations for infinitely configurable products, controlled suspension that can be individually configured by the customer may be just around the corner.
