MECHANICAL TRANSMISSION AND MAIN HYDRAULIC PUMP ASSEMBLY
The mechanical transmission and main hydraulic pump assembly (Figures 7 and 8) provide hydraulic pressure for powering
the winches, hoisting the boom and spade. It is mounted in the rear of the winch compartment, 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. 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 the 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 trapped between adjacent vanes as they move
past the inlet chamber. The fluid is then carried along a path of constant radius to the outlet chamber in the pressure plate. At this
point the radius of the cam ring's elliptical contour decreases, forcing the fluid into outlet chambers through pressure plate ports
and through outlet ports. Pump output high pressure is directed to the winches and cylinders to operate them.
Figure 7. Mechanical Transmission and Main Hydraulic Pump Assembly--Left-Front View.