(57) An apparatus (10) is described for controlling angular movement of a door (11), the
apparatus (10) including a housing (17) and a piston (20), having a longitudinal axis
(22), slidable in a cylinder (18) in the housing (17). The piston (20) has a transverse
opening (24) therethrough, with an inwardly facing wall (26) of the opening (24) provided
with a rack gear (28) having a plurality of teeth (29) which are substantially transverse
to the longitudinal axis (22) of the piston (20). The apparatus (10) also includes
a pinion gear (30) supported for rotation about its longitudinal axis (34) by the
housing (17) and extending through the transverse opening (24) in the piston (20),
the pinion gear (30) having a plurality of teeth (32) which engage with the teeth
(29) of the rack gear(28), such that rotation of the pinion gear (30) about its longitudinal
axis (34) effects sliding movement of the piston (20) through the cylinder (18). A
top land of each tooth (32) of the pinion gear (30) has two portions (53, 54) each
of which extends towards the longitudinal axis (34) of the pinion gear (30) at a homogenous
gradient as it extends away from the other side portion (53, 54). Alternatively, the
top land of each tooth (32) of the pinion gear (30) has a substantially central portion
(52), which is substantially parallel to the longitudinal axis (34) of the pinion
gear (30), and is provided between the two side portions (53, 54).
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