JLG E300 Service Manual - Manual (Page 72)

SECTION 3 - CHASSIS & TURNTABLE
3-38 – JLG Lift – 3120772
3.9 HELAC ROTARY ACTUATOR
Theory Of Operation
The rotary actuator is a simple mechanism that uses
the sliding spline operating concept to convert linear
piston motion into powerful shaft rotation. Each actua-
tor is composed of a housing with integrated gear
teeth (01) and only two moving parts: the central shaft
with integrated bearing tube and mounting flange (02),
and the annular piston sleeve (03). Helical spline teeth
machined on the shaft engage matching splines on the
in-side diameter of the piston. The outside diameter of
the piston carries a second set of splines, of opposite
hand, which engage with matching splines in the hous-
ing. As hydraulic pressure is applied, the piston is dis-
placed axially within the housing -similar to the
operation of a hydraulic cylinder while the splines
cause the shaft to rotate. When the con-trol valve is
closed, oil is trapped inside the actuator, preventing
piston movement and locking the shaft in position.
The shaft is supported radially by the large upper radial
bearing and the lower radial bearing. Axially, the shaft
is separated from the housing by the upper and lower
thrust washers. The end cap is adjusted for axial clear-
ance and locked in position by set screws or pins.
NOTE: Bars indicate starting positions of piston and shaft.
Arrows indicate direction they will rotate. The hous-
ing with integral ring gear remains stationary.
As fluid pressure is applied, the piston is displaced
axially while the helical gearing causes the piston
and shaft to rotate simultaneously. The double helix
design compounds rotation: shaft rotation is about
twice that of the piston.