A smoother ride for vehicle seats

A 1940s technology is being used to provide a smoother and more comfortable ride for truckers. Design Engineering investigates

Driver comfort has long been a major concern in the heavy-duty truck market. User fatigue along with a growing awareness of the connection between vehicle design and the operator has led equipment designers to look at many new technologies.

Recently, Lord Corporation has developed a magnetic fluid ride damping system for truck seating, that uses Rheonetic fluid in an electronically controlled damper in place of conventional hydraulics to absorb vibration. Called the Motion Master Ride Management System, it allows driver selectable ride modes (soft, medium, or firm) to provide a smoother, more comfortable ride on suspended seats found in large vehicles. This damper system has proven to smooth over the roughest suspension-challenging roads in the trucking world.

Rheonetic magnetic fluid shock absorbers use technology first discovered in the 1940s. Researchers discovered that by creating a suspension of magnetically polarisable particles it would be possible to change fluid viscosity by subjecting the fluid to a magnetic field. These fluids were termed, magnetorheological fluids or MR fluids. Until recently, the challenges involving particle settling and research into other fully active systems had kept the magnetic fluids from finding a market.

Rheonetic fluids typically consist of micron-size, magnetically polarizable particles dispersed in a carrier medium – most commonly mineral oil or silicone oil. Particle chains form when a magnetic field is applied. In the presence of a shear force, the equilibrium between the forming and breaking of particle fibrils corresponds to the fluid’s yield strength.

As the particles react to the magnetic field they form a dense network of chains, changing the fluid from a liquid to a near solid and back to liquid in a matter of milliseconds. When the fluid is used in a shock absorber application and coupled with electronic micro controls, a system may be created that instantly provides varying levels of softness or firmness to match changing levels of shock and vibration. The stronger the magnetic field, the thicker the fluid and the greater the vibration/shock suppression. The first commercial adaptation of this concept is in the Motion Master product for truck seating.

ELECTRONICALLY PROFILED

Creating a damper system that can be electronically profiled simply by changing the current applied to a magnetic field offers several advantages. First, customising the damper for a specific application requires only the modification of the magnetic field control algorithm. Second, fluid damping provides a quick response – 10ms to 15ms – and smooth performance for greater comfort (especially important in seat applications). The response curve is proportional to the applied current to the damper.

Semi-active Rheonetic products only remove energy from the system; they do not add energy. This fail-safe condition is similar to a passive shock. The semi-active approach requires little power – the peak is 4W. Average consumption is in the 1W RMS range. Also, low voltage power, typically 12V, is all that is required. Damping performance is independent of velocity providing high or low damping at any velocity.

By simply changing the amount of current through a coil in the rheonetic shock and vibration damper design, a process of resistance or dampening can be increased or decreased. In heavy vehicles, the driver seat is a suspension seat, complete with a passive shock absorber and air spring.

In passive systems, it is difficult to obtain the damping performance required at low velocity while maintaining a smooth ride at high velocity. The Motion Master ride management system avoids this problem because of the non-velocity sensitivity of the rheonetic damper. Accordingly, the Motion Master system provides a flat-velocity curve that can create the appropriate force at any velocity. In the real world, if high damping is required at low velocity, simply applying the appropriate algorithm magnetic field will cause the damper to provide the desired result. This level of performance is not available with traditional hydraulic dampers.

There are four basic components to the Motion Master ride management system. The ride mode switch allows the operator to choose from three different ride settings providing the desired comfort through all driving conditions. The position sensor maintains movement of the seat caused by changing road and operating conditions. The controller electronically updates information on seat position up to 500 times per second.

In response to information from the position sensor, the controller determines the intensity of magnetism to be applied to the fluid in the magnetic damper. The magnetic damper contains MR fluid which responds to the controller with an appropriate fluid thickness within seconds, and delivers the exact amount of force needed to counteract the occurring shock or motion. Drivers particularly notice the improved response to shock and vibration that would normally send the seat into violent topping and bottoming. With the Motion Master system, the bumps are smoothed out no matter how rough the road.

While the rheonetic technology has initially been applied to a ride management system for heavy truck seating, the technology has promise for far reaching applications in a wide variety of areas within industry.

Lord Corporation Tel: 919-468-5979