Science / Medicine : Revolutionary Hydraulic Fluid Considered a Technological Boon

Automobile clutches with no moving parts. High-performance shock absorbers that adjust instantly to changing road conditions, yet cost no more than conventional shocks. Robotic arms that are much more sensitive and responsive than those now in use.

Those are but a few of the potential applications of a revolutionary new hydraulic fluid patented last week by University of Michigan researchers.

The fluid solidifies when an electric field is applied, then returns to its liquid form when the field is released. This ability would allow fluid switching devices, clutches, transmissions and other devices to be controlled directly by a computer without intermediate mechanical components.

The first such fluid was developed 40 years ago, but neither it nor others developed since have had practical applications, primarily because they break down at the temperatures encountered in cars and other machinery. The Michigan material is the first to overcome that problem. Experts say that potential applications of the technology represent a $20-billion annual business.

The new fluid represents “real product innovations that are very feasible very soon,” said David D. Hunter, vice president of Acustar Inc., a Chrysler Motor Corp. subsidiary that has licensed the technology for use in four-wheel drive vehicles.

Fluids like the new material are called electro-rheological fluids because they thicken in the presence of an electrical field. Those developed in the past typically consisted of a fine powder such as baking soda, glass or even corn starch dispersed in an electrically non-conductive fluid such as kerosene or silicone oil. They always contained water, which limited their operating temperature.

In the absence of an electrical field, such fluids typically look like milk. As an increasing electrical field is applied, the fluid thickens to the consistency of cream, then of butter. At very high fields, the congealed solid can withstand large forces of shear, tension and compression, said physicist Frank E. Filisko, the new material’s inventor.

Although a field of several million volts is required to congeal the fluids, virtually no current passes through the material. Thus, if the fluids could be used in an automobile, for example, its battery could furnish the required power. When the field is turned off, the material instantly reverts to its fluid form.

Filisko’s discovery was that a family of materials called aluminosilicates--made from aluminum, silicon, and oxygen--would work in such fluids in the absence of water.

Not Sure How Fluids Work

Scientists are not really sure about how the electro-rheological fluids work. “We have a new theory that helped us select the aluminosilicates, but I am not going to talk about it until we study it more and publish a paper,” Filisko said. He noted that his group was fortunate that the aluminosilicates were one of the first materials they tried; other materials they have tried since do not work as well as predicted by the theory.

Filisko estimated that the new materials could cost as little as $3 per quart, compared to $40 or more for existing electro-rheological fluids.

One potential use of the new fluids might be in shock absorbers where they could change from normal to viscid and back again in a fraction of a second under the control of a microcomputer. It would thus be possible to alter the damping effect of individual shock absorbers independently in response to changing road conditions.

Such shock absorbers could be built for a fraction of the cost of conventional independent suspension systems, Filisko said. Used in brakes, the fluid would allow smooth braking with no lockups because the brake on each wheel could be controlled independently by microcomputers, he said.

In hydraulically powered robotic arms, use of the new fluid would eliminate the need for solenoids--mechanical switches for controlling the fluids--and would greatly decrease the response time of the devices, he added.

The primary licensee of the new technology is Tremec Trading Co. of Farmington Hills, Mich., which manufactures manual automobile transmissions and which supported Filisko’s research. The company is already studying the fluid’s use in a variety of mechanical devices, said Ed Kaiser, Tremec’s manager of technical sales, but he could not predict which products would be first to market.

“It’s completely changing the way we think about products, so we’re not sure yet which is going to be best,” he said.