by Jim Kerr
Shock absorbers are a key component of all automobiles. They control the vehicle’s suspension movement to provide a stable, comfortable ride. Since they were installed on the first automobiles, the principle of shock absorber operation has remained essentially the same. Now a new type of shock absorber is entering the market, and it may change the way suspensions are controlled. They call it MagneRide.
Designed by Delphi’s Energy and Chassis Systems division, MagneRide first appeared on General Motors’ 2003 Corvette Anniversary Edition and the 2003 Cadillac Seville STS. MagneRide is a continuously variable shock absorber that uses simple magnetic principles but very high technology to control suspensions.
Conventional shock absorbers (or struts on many cars) use oil passing through orifices to dampen suspension movement. When a tire hits a bump, the suspension moves up, moving the body of the shock absorber up too. A rod, connected to the top of the shock and mounted to the body or frame, passes through a seal in the top of the shock and has a piston mounted on the bottom end. This piston has small ports in it that allow oil contained in the shock body to flow from one side of the piston to the other. Different size ports allow different flow rates, so larger ports allow the suspension to move easier and smaller ports slow the movement.
Conventional shock absorbers use check valves on the ports so that fluid can pass easier one way than the other. Typically, the wheel is allowed to move up quickly, but let back down slower. This prevents the suspension from bouncing; the effect you get when the shocks are badly worn.
Gas-filled shocks use pressure inside the shock to reduce oil foaming as it passes through the ports. Suspension control becomes very erratic with foamy oil inside the shock. Vehicles with selectable shock dampening vary the size of ports by turning a shaft inside the piston rod that changes port size to change vehicle handling. MagneRide makes mechanically varied systems obsolete.
The heart of a MagneRide shock is the Magneto-Rheological (MR) fluid. It is a suspension of magnetically soft particles such as iron microspheres in a synthetic hydrocarbon base fluid. Place a magnet near the fluid and the particles form a fibrous structure, increasing its shear factor. In simple terms, the fluid gets thicker so it doesn’t flow through the shock’s piston ports as easy.
By using an electromagnet placed in the shock piston, the MR fluid only changes viscosity where it passes through the ports. Wires run down the hollow piston rod so a computer module can vary the strength of the electromagnet and the dampening of the shock continuously. The system is five times faster than mechanical ride control systems.
In fact, the system is so quick, it performs 1000 calculations per second. This is equal to one calculation for every inch of vehicle travel at 60 miles per hour. MagneRide can react to every little bump in the road.
Several sensors provide input to the MagneRide computer. Wheel to body sensors are used at each wheel to determine wheel travel and vertical acceleration. Vehicle speed and outside temperature come via data communication from other vehicle computers. The temperature data is used so the computer can compensate for fluid viscosity variations due to temperature. MagneRide also improves vehicle stability control systems and uses a steering wheel angle sensor, yaw rate sensor and lateral acceleration sensor for accurate vehicle control.
For the auto engineers, MagneRide allows quicker calibration and suspension tuning for new vehicles. For drivers, MagneRide offers a flatter, smoother ride, enhanced lateral and longitudinal control of body movement, and better road isolation from the passenger compartment. While MagneRide has limited availability now, I predict we will see this feature on a wide range of automobiles in the near future.