neutral, the shuttle valve (located in the hydrostatic
motor manifold) is centered allowing oil from the charge
7-109. SHUTTLE VALVE.
pump to be directed to the cooling circuit by the low-
7-110. When in neutral, the shuttle valve directs oil flow
charge-pressure relief valve. Cooling circuit flow in
to the cooling circuit. The shuttle valve prevents loss of
neutral is not admitted to the motor, but is directed to
high pressure oil when transmission is reversed.
the pumps' drain circuit, through the oil cooler to the
7-111. CONTROL FUNCTION.
7-112. The charge pump provides oil under pressure to
7-105. OIL COOLER.
7-106. The oil cooler is mounted with the engine
radiator. It is connected between the motor case drain
7-113. MAKE-UP CIRCUIT .
port and the hydraulic tank. Excess cooing oil from the
7-114. The charge pump provides oil to the circuit to
low-charge- pressure relief valve enters the motor case,
make up for internal leakage.
then flows through the case drain line through the pump
case to the oil cooler and the tank.
7-115. HYDROSTATIC PUMP ASSEMBLY .
7-116. The hydrostatic transmission employs a variable
7-107. OIL COOLER BYPASS VALVE.
displacement hydraulic pump driving a fixed
7-108. The oil cooler bypass valve prevents high back-
displacement hydraulic motor to transfer engine power
pressure at the pump case. Back- pressure can result
to the final drive.
from cold fluid or a restricted oil cooler passage. The
7-117. The hydrostatic pump assembly is attached to,
valve is set to open at 15 PSI (1.05 kg/cm2) pressure at
and driven by, a hub assembly on the engine flywheel.
normal operating temperature. During cold start
conditions or if flow through the cooler becomes
7-118. VARIABLE DISPLACEMENT
restricted, the valve opens to allow flow from the pump
directly to the hydraulic tank.