Appeal 2007-0388
Application 10/337,459
Harvey addresses the problem of "creep," which can cause the billet to
deform and create a hole in the passage without the billet changing from
solid to liquid, thereby letting pressurized air from the tire flow through the
passage, such flow also potentially cooling and hardening the billet and
reclosing the hole, preventing the fuse device from operating in its intended
manner to avert danger (Harvey, col. 1, ll. 46-56). Harvey does this by
forming the device with a cruciform housing 11 comprising a branch 14
aligned with a branch 16 and having a longitudinal bore 12, for locating the
billet of eutectic material 19 and a piston 20 provided with O-ring 21, and a
transverse bore 13 for venting tire pressure (Harvey, col. 3, l. 38 to col. 4, l.
9). The eutectic material is selected to have a melting point corresponding
to a potentially dangerous temperature for a tire mounted on the wheel. If
such a temperature is reached, the eutectic material of billet 19 is converted
from a solid to a liquid state and piston 20 will displace the eutectic material
through the opening 17 of longitudinal bore 12 under the influence of tire air
pressure. When the O-ring 21 clears the inner end of bore 12, the
pressurized air from the tire is vented through the two branches of the
transverse bore 13. (Harvey, col. 3, l. 65 to col. 4., l. 9.) An annular step or
shoulder 18 at the free end of the branch 16 is provided to define a reduced
end opening 17 in bore 12 and to abut billet 19 (Harvey, col. 3, ll. 48-54).
Flat surface 18 tends to prevent the billet from progressively losing its shape
as a result of being brought repeatedly to a temperature approaching its
melting point, thereby preventing the billet 19 from discharging air from the
tire unless the billet is fully changed from a solid to a liquid state (Harvey,
col. 4, ll. 13-19). Since the melting eutectic material flowing through
opening 17 is isolated from pressurized air venting from the tire by piston
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