Fluid Control By Wire

Lord Corp.'s orders for its Tactile Feedback Device rose sharply this year, a result of surging interest in the devices for x-by-wire applications, says Jim Toscano, manager of global sales and marketing for the company's materials business. What Lansing Linde in the U.K. started a few years ago in forklift steer-by-wire systems moved into the powerboat market last year. AB Volvo Penta introduced a steering system that uses the Lord device to provide helm "feel" for a steer-by-wire rudder. Lord now offers the device to industrial designers in two torque configurations, 12 and 5 Nm, for immediate integration or evaluation, Toscano says.

MR, or magnetorheological, fluids change from liquids to near solids in the presence of magnetic fields. Lord uses the fluid in its feedback system to mimic the resistance a driver steering a linked system would feel as he turned the wheels sharply. The fluid exhibits a "yield stress that's proportional to the magnetic field strength," explains Marketing Manager Doug LeRoy, "while providing fast response time and a fine degree of control."
The devices can generate variable feedback, detents, or hard stops as haptic indications of a reach truck's wheel orientation, for example, which the operator ordinarily can't see.

By-wire applications of the device are not limited to steering, Toscano adds. Brakes, clutches-joysticks, even-use the devices. Sales of the MR fluid itself has increased this year as well. Delphi Automotive uses it in its line of Magneride shocks. Military vehicles apply it for their wheel and track suspensions. European agricultural equipment makers are looking at the technology for cabin mounts, LeRoy says.

MR fluids had their start in the early 1990s, Toscano says, after the company experimented for a few years with electrorheological fluids. They languished as solutions in search of problems until 1998 when they began showing up in seat suspension dampers. They've now "moved from curiosities to viable tools in the engineer's toolbox," Toscano says.

Lord manufactures MR fluids in hydrocarbon-, water-, and silicon-based varieties. The company recommends oil-based fluid for dampers, shocks, and struts; water-based for mounts, demonstration devices, and toys; and silicon-based for mounts and dampers.

MR tactile feedback may one day accompany steer-by-wire systems in our cars, he speculates. Before they do, though, there'll be an expanse of regulatory terrain to cross.