Active engine mounts
Active engine mounts reduce the transmission of vibrations from the engine to the crew compartment while ensuring a sufficiently rigid attachment of the power unit to the body.
Rubber mounts are today a traditional way of attaching the unit to the bodywork. However, they must meet two conflicting requirements. On the one hand, it’s about firm attachment of the unit, which will eliminate undesired movements of the unit in the bodywork. On the other hand, it’s about a sufficiently flexible attachment eliminating the transfer of vibrations from the shaking aggregate to the bodywork, and subsequently to the crew. Unlike traditional mounts, active engine mounts allow changing their characteristics while driving, thereby covering more operational states.
Active mounts are nothing new, since 1990, Honda began using them in the Accord model. Several years later, Jaguar XJ 2.7D twin-turbo (2006) also received active mounts. These mounts helped practically eliminate all vibrations caused by the operation of its diesel engine at idle. In 2007, electronically controlled mounts were also installed in the Hyundai Veracruz, not only for diesel engines but also for gasoline ones. The setup consisted of three passive and one active member for vibration elimination.
In 2007, Lexus RX350 and Toyota Camry received a system of active engine mounts called Active Control Engine Mount (ACM). In this case, the rear part of the engine was supported by a hydraulic mount, which eliminated vibrations and noise. The front part of the unit was connected using electronically controlled mounts that adapted to the current conditions. In principle, these mounts utilized a magneto-rheological fluid.
In 2011, the Audi S8 and Audi RS7 received a new 4.0 V8 TFSI eight-cylinder engine, replacing the original 5.2-liter six-cylinder one. The new engine, due to emission limits and consumption, was equipped with a Cylinder On Demand (COD) system. However, running the new eight-cylinder engine on 4 cylinders creates slight vibrations, which a regular eight-cylinder naturally eliminates. To prevent the comfort from deteriorating with the new COD system, it was supported precisely by active mounts, which dampen the engine’s operation and its vibrations with phase-shifted vibrations.
So far, we have described the influence of active mounts on driving comfort and the amount of vibrations transmitted to the cabin. However, Porsche looks at the unit movements also from the perspective of driving dynamics. Porsche engineers named their system of active unit support Dynamic Engine Mount System.
