Tech Briefs
Valveless damping suspension system

Cutaway of a MagneRide rear damper.

MagneRide, a suspension-control system developed by Delphi Automotive, is a semi-active system based on fully integrated algorithmic control. According to Delphi engineers, the application of magneto-rheological (MR) fluids enable instantaneous responses, high performance levels, virtually silent operation, and the elimination of electromechanical valves.

MR fluids are produced by suspending carbonyl iron microspheres or other magnetically soft particles in a base fluid of synthetic hydrocarbon or silicon. The Delphi-developed MR fluid used in the MagneRide's dampers feature a "bimodal" particle-size distribution that incorporates two sizes of iron microspheres—large and small. In operation, the system's electronic control unit (ECU) sends electrical currents up to 1000 times per second to electromagnetic coils housed in the dampers. By controlling the current to the coils inside the piston of the damper, the MR fluid's yield is changed, varying the resistance to flow. The applied magnetic field aligns the metal particles into fibrous structures, changing the fluid rheology to a near-plastic state and controlling the fluid's yield stress without affecting its viscosity. The company says that the result is continuously variable real-time damping that provides a flatter ride during cornering and reduced dive and squat during braking and accelerating, with immediate adjustments to a stiffer suspension for more difficult or unexpected driving situations.

The damping actuators are struts or shock absorbers that are gas-charged, monotube designs without valves or any other small moving parts. Delphi says that valveless dampers provide a smooth, laminar flow of the MR fluid that is quiet, unlike valve-based systems that are prone to noisy, turbulent flows in the dampers. Because the performance of laminar flow is very predictable, the mechanical characteristics of the damper can be designed and controlled to accurately meet design specifications to within 2-3%.

MagneRide uses a simplified sensor-set consisting of a displacement sensor at each vehicle corner, a lateral accelerometer, and a steering hand-wheel displacement sensor. These sensors determine absolute velocities of the body heave, roll, and pitch motions. The algorithm and ECU use this input to control the distribution of the normal load through the tire patches by varying the level of damping at each corner of the vehicle depending on the conditions of the vehicle's motion, as well as driver inputs such as steering and braking.

MagneRide is a further improvement of Delphi's valve-based damping systems currently offered by Cadillac (Stabilitrak) and Corvette (Active Handling). Delphi expects the first MagneRide systems to appear on passenger vehicles in 2003.