Contoured air spring adds NVH quality to McPherson struts

Denver, Co--For years, premium automakers have known a simple way to optimize the performance of McPherson struts: Use dual path isolation mounts, which separate spring vibrations from shock absorber vibrations.

Unfortunately, dual path mounts haven't been compatible with air springs. As a result, automakers who wanted the high performance and light weight of an air spring in a McPherson strut were denied the luxury of dual path mounts.

Now, however, that may be changing. Engineers from The Gates Rubber Co. have developed a technique that enables them to combine air springs with dual path mounts on McPherson struts. By contouring the springs--thus placing more volume where it's needed and less where it's not--Gates engineers solved the problems that kept air springs out of those applications. As a result, automakers who use strut-type suspensions can now offer premium quality isolation with an air spring.

Key to the new development is the shape of the spring. By employing a proprietary technique that allows engineers to vary the helix angle of the spring's reinforcement, Gates has created an air spring that has a controllable and variable diameter along its length. As a result, the company's engineers can add or subtract diameter from the so-called "volume portion" of the spring, and do the same with its "rolling lobe."

That's critical because it enables Gates engineers to customize the air spring to meet the specific needs of McPherson strut suspensions. Up to now, air springs have not served well in such applications. The reason: They weren't good at compensating for side loads. What's more, they didn't allow for use of dual path mounts.

The contoured air spring solves those problems because it can be customized to compensate for side loads and it can be applied with dual path isolation mounts. In tests, Gates engineers say their AirSpring has achieved 100% side load compensation while using dual path isolation mounts. In contrast, past efforts with air springs in McPherson struts resulted in less than 70% side load compensation.

Gates engineers accomplish that by employing a large diameter near the top, or volume portion, of the spring. At the bottom, or rolling lobe, they employ a much smaller diameter.

In that sense, Gates' AirSpring distinguishes itself from conventional air springs. "With conventional air springs, you have a choice of diameters," notes Mike Crabtree, the Gates engineer, who invented the system along with colleague Dick Stieg. "It can be one diameter, or it can be another, but it can't be both."

By offering variable diameters, the Gates design allows the spring to serve specific functions. The large diameter portion helps handle side loads. The spring's smaller rolling lobe enables the AirSpring to more easily meet packaging constraints. It also prevents the spring's stiffness from growing so great that it would change the performance of the suspension. "If you make the diameter large over the entire length, the spring rate could be as much as four times too high," Crabtree says.

As a result, the Gates design allows automakers to obtain the capabilities that air springs can provide, while also supplying them with the NVH advantages of dual path isolation mounts. "The shape of the AirSpring is the key to this," Crabtree concludes. "If we didn't have the ability to control the inflated shape, we couldn't do it."

Additional details...Contact Steve Obrand, The Gates Rubber Co., 990 South Broadway, P.O. Box 5887, Denver, CO 80217, 303-744-1911.

Other Applications

- Motorcycle suspensions

- Rear automotive springs

- SUV suspensions