BWIGroup, a leading global supplier of ride control systems, has recently introduced into production a powertrain mount using magneto-rheological technology. Magneto Rheological (MR) fluid has magnetically soft particles suspended in a fluid base. These align themselves proportionally to an applied magnetic field and thus changes the shear stress required to move the fluid. This property can be used to control stiffness and viscous damping in automotive components.
The mount contains an electromagnetic coil that can generate a variable magnetic flux across the fluid passages. When the coil current is off, the MR fluid is not magnetised, the iron particles are randomly dispersed within the fluid, and the fluid behaves like conventional hydraulic oil. When the coil is energized, the magnetic field causes the particles to align into fibrous structures in the direction of the magnetic flux. The strength of the bond between the particles in the structures is proportional to the strength of the magnetic field, so changing the current provides real-time variable damping with a very large range of force variation.
Mount Stiffness and Damping can be adapted to multiple vehicle conditions giving greater attribute performance for refinement, dynamics, and driveability.
Unlike conventional hydraulic mounts, which provide peak damping at a single frequency and amplitude, the MR Mount provides high damping over a broad frequency and amplitude range. The MR technology also allows for the dynamic rate to be instantly changed between the base dynamic rate of the rubber-moulded assembly and the moulded assembly’s bulge rate. Most applications can benefit from using a softer base rate moulded assembly as the required stiffness increase under large amplitude events can be achieved by altering the force required to push the fluid through the orifice.
The MR Powertrain mount, under microprocessor control, adjusts mount damping and dynamic stiffness as a function of vehicle state. An onboard controller receives information about vehicle state and feedback from mount’s pressure sensor, and outputs a predetermined optimal amount of current.