Some auto manufacturers call it “downsizing," others insist on the term “rightsizing” as they doggedly pursue smaller engine designs that also include cylinder deactivation and stop-start systems to help bring radical emissions and fuel consumption improvements.
But there is another word that is associated with both: “compromise." In the automotive realm, compromise almost invariably goes hand-in-hand noise, vibration and harshness (NVH).
Solutions are varied, but some manufacturers consider a fundamental aspect of tackling NVH is to take a fresh and innovative approach to powertrain isolation.
BWI Group, supplier of advanced chassis technologies, believes its second-generation Magneto Rheological (MR) powertrain mounts mitigate compromise by combining effective control of powertrain motion with good attenuation of noise and vibration. The company claims this simultaneously improves vehicle stability while more effectively isolating cabin occupants.
“The first-generation MR mounts prevented large transient powertrain events in the range of 2-22 Hz from reaching the chassis,” explains Tim Schlangen, the Group’s Mounts Engineering Manager. But further research and development had delivered added gains, he said: “Gen 2 retains this capability while also isolating the chassis from smaller-amplitude movements in the range 30-150 Hz. It is this range that is critical for refinement.”
Maintaining control of the vertical force at each tire is a key priority for chassis engineers—but this much-desired control can be affected by powertrain movement unloading the contact patch intermittently, especially during large torque transients or on bumpy roads, he said.
This effect is further complicated by the dynamic interaction between the vehicle’s suspension and engine mountings. Previously, this meant that suspension settings were sometimes compromised in order to cope with specific engine vibration modes.
Conventional engine mounting strategies to limit powertrain movement by increasing the mounting stiffness can lead to NVH issues, as vibrations are transmitted more readily to the cabin.
Schlangen states that BWI’s adaptive powertrain mount was originally designed to improve the performance and handling of premium sports cars. But due to growing demand from its customers, the second-generation MR engine-mount technology has been specifically developed to improve vehicle refinement.
Evolving from sport to luxury
MR technology was first incorporated in the company’s adaptive damper system, MagneRide, in 2002. The technology has been adopted by several major manufacturers including Audi, Jaguar Land Rover and GM and now is in its 4th generation. MagneRide is designed to improve chassis-development compromises between handling and comfort.
As with MagneRide, BWI's new engine mounts use MR fluid to change the damping rate in real time, said Schlangen: “The second-generation mounts can operate over a wider frequency range than their predecessors, partly due to the inclusion of a decoupler system, which provides a secondary path through which the MR fluid can pass to reduce the mount stiffness when required.”
Developing a decoupler to work with MR fluid was particularly challenging because it is notably denser than conventional passive-mount glycol fluid. Much of the technology in the decoupler, such as the rubber and metal component geometry and the rubber formulation drew on “core skills” within BWI to develop solutions that remain proprietary to the company, explained Schlangen.
Together with the decoupler, the refinement of internal components, including the copper coil and magnets of the Gen 2 MR mounts, provide faster response; the mount stiffness can be varied more quickly for more-accurate control. The control software also has increased functionality, designed to provide engineers with enhanced precision and added flexibility. The combined effect of the advances has been to achieve what Schlangen described as a “more streamlined development process that reduces the need for test track time and access to costly, bespoke development vehicles." It also enables the mount to be applied to a wider selection of vehicle segments, not just premium sports models.
By increasing the range of frequencies managed by the system, the Gen 2 technology extends the scope of application beyond high-performance cars to now include those where the emphasis is on refinement.
A C-segment future?
“As with most new technologies, we expect the product to be first used across the more premium end of the market. However, the mounts are a very cost-effective method of improving NVH levels, so we anticipate adoption in D-, and possibly C-segment vehicles too,” revealed Schlangen.
“The standards to which modern cars are engineered are so high that brand differentiation is often linked to refinement because it drives the perception of quality. According to feedback from our drive appraisals with European OEMs, vehicle occupants experience a dramatic increase in the perception of quality, stability and security as a result of reduced vehicle shake when using the new mounts.”
Schlangen added that the company's second-generation MR mounts now are entering production with a (so far unnamed) European vehicle manufacturer in an application where a four-cylinder engine is a direct replacement for a six: “The combination of NVH control and calibration flexibility provided the OEM with the ability to tune the characteristics of the mount to align with brand requirements.”