TM 9-2350-256-34-2
under the crew compartment. The main engine drives the mechanical transmission in one direction of rotation
only, through a propeller shaft and universal joints. The transmission has a single-speed reduction and
consists of herringbone tooth gears, a lubrication and pressure pump, a high and low pressure valve and a
hydraulically operated disk clutch. The transmission housing provides a reservoir for the oil which is used for
lubrication and actuation of the disk clutch. The output shaft of the transmission is coupled to the input shaft of
the vane-type, fixed-displacement, hydraulic pump. Mounted on top of the pump is a relief and unloading
valve, which consists of spring-loaded valves opposed by hydraulic pressure.
Figure 1-11. Mechanical transmission and main hydraulic pump assembly right rear view.
(2) Operation. When the main engine is operating, the input propeller shaft rotates, supplying input
power to the transmission gear train and drive to the lubricating pump. When the power control valve is placed
in the ON position, hydraulic pressure from the pressure pump is directed to the pressure valve to the clutch
cylinder, overcoming the clutch spring force, and engaging the clutch disks. With the clutch disks engaged,
rotational force is supplied to the output shaft of the transmission, which is coupled to, and drives, the pump
shaft. Spline mounted to the drive shaft are two rotors, complete with vanes, which are spring-loaded in the
slots of the rotors. These vanes follow the elliptical internal contour of the cam rings. As the vanes move
across an inlet in the body, the radius of cam ring's elliptical contour increases to create a space between the
rotor and the cam ring contour. Fluid flows into this space and is
1-14 Change 2