Internal Name: Side-by-Side Helical Spring

What’s New: This push-pull valve-centering spring is a double side-by-side helix bent from a single piece of spring wire, without expensive ground ends. Separate allowed claims cover the spring itself and an inexpensive clamping system to handle the reversing spring force without damaging the spring wire. The spring fits compactly into the rectangular envelope available to electric valve actuators packed side-by-side along a cylinder head. The spring goes in the top of the actuator, working against a conventional-size valve return spring in the cylinder head with standard lash adjustment, thus eliminating the need to re-tool the cylinder head to accept the larger return spring required for use with some electric valve actuators. Operating almost symmetrically about a neutral bias point, the spring wire handles a higher ratio of stored energy to weight, thus reducing moving mass and improving actuator speed.

Status: Issued U.S. Jan. 29, 2002

Why: Compression springs are adapted to provide spring force in one direction. Electric valve actuators use two compression springs preloaded against each other to achieve bi-directional restoration. The preloaded spring metal handles less cyclic stress than metal operating symmetrically about a neutral bias. Thus, a more massive spring is required for a given cyclic energy requirement, leading to slower actuation. Both of the preloaded springs in an electric valve actuator are larger than a conventional valve return spring. The lower of these two springs, pushing up on the valve where a smaller conventional return spring was once located, requires cylinder head rework. A side-by-side helical spring fits efficiently into a rectangular space at the top of the magnetic actuator, reducing overall moving mass and restoring the valve return spring to its original configuration, with reduced force on the lash adjustment interface.

How: As best viewed in the patent drawings or from our photos and solid models, a single length of spring metal is bent into side-by-side helices, each sharing the same helical rotation sense (both right-hand or both left-hand helices), with the two helices joined by an S-shaped bridge. The two ends are held in fixed clamps while the middle of the bridge is captured around the wire circumference in a low-mass compression clamp. This clamp, like the end clamps, is lined with a hard rubber, preloaded so that all highly stressed rubber is always in compression. The large forces that transfer spring force arise almost entirely from differences in compression – pure positive pressure – rather from shear forces. Like a liquid, rubber has an almost unlimited capacity to withstand pressure without damage. Shear forces, which could potentially rip the rubber in shreds, are very small. Perhaps the greatest innovation in this spring design is not the double helix, but a way to transfer a reversing linear force out of a spring wire without damaging the wire or the material that captures the wire. This is an unexpected marriage of a relatively soft polymeric elastomer with hardened steel.

Download: Spring for Valve Control in Engines U.S. 6,341,767 Joseph Seale, Gary Bergstrom

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