The design, development and applications of MagneRide suspension

How much force is required depends on how much damping effort the suspension engineers want, and that will relate to factors like the strength of the springs and whether the car is designed primarily for performance or comfort. 

The design of the valves and viscosity of the fluid determine how much effort it takes to move the dampers. Most dampers are fixed rate but cars with ‘sport’ settings are often equipped with electrically adjustable valves to change them from a harder to a softer setting by increasing the size of the opening that the fluid has to flow through.

The mechanical design of the MagneRide damper is less complicated. There are no valves, just passages to allow the fluid to pass through the piston as it moves. 

What changes to adjust the damper from soft to hard is the fluid. The secret behind MagneRide lies in a technology called magnetorheological (MR) fluid, a kind of synthetic oil containing tiny particles of iron in suspension. 

The latest MagneRide system is equipped with electric coils which, when energised, create an electromagnetic field. When that happens, the iron particles align, effectively increasing the thickness of the fluid by creating rigid structures, making it harder to push the fluid through the channels in the piston when it moves. This increases the damping force.

The stronger the field, the more the particles align and the greater the damping force. When the electrical current is switched off, the magnetic field collapses, the iron particles separate and the MR fluid passes easily through the pistons, reducing the damping force.

Again, the concept sounds simple, but one of the challenges when the fluid was first developed was to come up with a formulation that didn’t allow the iron particles to settle out, especially if the damper was unused for a period of time.  

Olivier Raynauld, BWI technical specialist, says: “MagneRide is a system. The dampers themselves are actuators but they are driven by a complex control system.” 

Like the car’s powertrain, MagneRide has its ECU, which monitors the car’s dynamic state and driver input, usually through existing sensors used for functions like ESP, pre-crash systems and ABS, as well as sensors which monitor the vertical movement of the dampers.

The third-generation MagneRide differs from previous versions by having two coils instead of one for each damper piston. Two coils allow the system to react faster, not when it’s activated, but when it’s de-activated. 

When a single electromagnet is turned off, electrical eddy currents cause the magnetic field to linger, only for a few milliseconds, but enough to prolong the damping force longer than is required.

“We’re only talking tiny increments here but it’s enough,” explains Raynauld. By using two coils wound in opposite directions, eddy currents cancel each other out and the magnetic field collapses almost instantaneously, improving the reaction time of the damper from 25 milliseconds to just 13 milliseconds. 

As the MagneRide control system has the potential to react to the car’s movements and issue a new command every single millisecond, this improvement made a difference. 

“Nobody believed 12 milliseconds was going to be significant until we put it in a car and people were able to experience the difference,” says Raynauld.