Modern consumers are a demanding bunch. We don’t just want bigger screens on our phones with more accurate capacitive touchscreen capabilities, we also want them to have unbreakable glass. We don’t just want our soda to have great flavor, we also want it to have zero calories. In short, we want to have our cake and eat it too. This is especially true in the automotive world. We want a car that rides like a dream while going 200 miles per hour and getting 500 miles per gallon. While we aren’t at a point where we can build a car that accomplishes all of that, modern technology has led to suspension systems that can change to react to different driving conditions, which brings us one step closer to achieving the dream of a car that can do it all.
In this article, we are going to cover the most successful semi-active suspension technology to hit the automotive world in the past decade. To do so, we start with one word: magnetorheological. For most people, that word doesn’t mean much. It sounds like something out of X-Men. Whether you know the word or not, it’s been heralding a change in the world of automotive suspension. Before I can explain what it is and why it’s important, I need to give a bit of a background information.
While there are a seemingly infinite number of different suspension setups and styles, the essence of a suspension system consists of two things: a spring and a damper. The spring is designed to absorb the force that results from the vertical movement of the wheel relative to the chassis, which can be caused by either an irregular road surface or body roll.
The three types of springs are coil springs, leaf springs, and torsion bars. When a spring is released after compression, it will expand to release the stored energy. Without a damper (and frictional losses), the force of this expansion would be transmitted to the body of the car and the spring would continue to bounce back and forth in what is known as simple harmonic motion. As you can see in this video, that doesn’t lead to exceptional stability. Dampers (or shock absorbers, as they are often called), do not actually absorb “shocks.” As mentioned prior, the spring absorbs the force; the shock absorber serves as a damper that reduces the bouncing (oscillation) of the spring. This helps to smooth out the ride and to keep the tires on the road.
Thanks to a gentleman named Earl MacPherson, who pioneered the MacPherson strut seen above, most people have an incorrect concept of suspension components. A MacPherson strut combines both the spring and the shock absorber into one assembly, which is often called a “shock,” as in “Bro, I’m totally going to get some performance shocks for my rusted-out ’95 Civic.”
The two components of the MacPherson strut are still distinct and can be upgraded individually, which will affect the performance of the assembly and the ride of the car. Installing soft springs will give a smooth ride, but will sacrifice performance due to body roll. Alternatively, installing shock absorbers that are very resistant to deflection will limit the springs’ ability to absorb force, by decreasing the period of harmonic oscillation, which can lead to improved handling. What can we do if we want the best of both?
Now that we have a basis for our discussion, let’s get back to the topic at hand. Magnetorheological fluid, often abbreviated as MR fluid, consists of micron-sized iron particles in a hydraulic fluid. Under normal conditions, the iron particles in the fluid are distributed randomly and, because they only make up 20 to 40% of the fluid, the fluid behaves as if there weren’t any particles in it. This means that the viscosity, or resistance to flow, of the fluid is unaffected.
The “magneto” part of the word above should give some clue to what is about to happen: Electromagnets produce a magnetic field, which causes the particles to align into fibrous structures. These structures increase the effective viscosity of the fluid, which increases the damping of the shock absorber. The strength of the magnetic flux can be varied, which allows the effective viscosity of the fluid to be varied to meet changing road conditions.
The most popular system of MR shocks in use today is the MagneRide system, which can also be abbreviated as MR. It was developed by the Delphi Corporation and debuted on the 2002 Cadillac Seville STS. These days, you can find it under the brand name BWIGroup on quite a few cars from brands like GM, Audi, Lamborghini, and Ferrari. There are other styles of active suspension, such as the Kinetic setup on the Maclaren MP4-12C, but that is different from a MR system. MR setups offer a blend of the reliability of traditional suspension with the performance of active systems. They are typically lauded by critics and enjoyed by enthusiasts.