Toro Groundsmaster 4500-D Series Service Manual page 143

Forward Direction Fan Operation
Groundsmaster ® 4500-D/4700-D
19245SL Rev A
A four section gear pump is coupled to the piston (traction) pump. The final
gear pump section (farthest from the piston pump) supplies hydraulic flow for
the hydraulic engine cooling fan motor.
The fan control manifold controls the operation of the hydraulic motor that drives
the engine cooling fan in addition to including the flow divider for the steering
and lift circuits. The electronically controlled proportional relief valve (PRV) in
the manifold controls the oil flow to the fan motor. The fan control manifold
controls the speed and direction of the fan motor based on electrical output
from the TEC controller (T1).
Oil flow from the gear pump section to the cooling fan motor is controlled by the
proportional relief valve (PRV) in the fan control manifold. This valve adjusts fan
circuit flow based on a PWM (Pulse Width Modulation) signal from the TEC
controller (1). The controller uses engine coolant and hydraulic oil temperatures
as inputs to determine the proper PWM signal for the PRV valve. The fan circuit
flow determines the speed of the cooling fan motor.
•
The fan motor runs at half speed until coolant reaches approximately 74 ºC
(165 ºF). The fan motor increases to full speed (approximately 2800 RPM)
as coolant reaches 82 ºC (180 ºF).
•
The fan motor automatically reverses if coolant reaches 95 ºC (203 ºF) or
hydraulic oil reaches 100 ºC (212 ºF).
If the cooling fan motor is stalled for any reason, the manifold proportional
relief valve (PRV) has a secondary function as a circuit relief to limit fan motor
pressure to 207 bar (3000 PSI).
When the engine is shut off, the over-running inertia load of the fan blades
keeps driving the fan motor and turns it into a pump. The check valve (CV) in
the fan control manifold will open to keep the motor circuit full of oil so the fan
motor will not cavitate.
Note: If PWM current is not available to the fan control manifold proportional
relief valve (PRV), the cooling fan motor will run at full speed in the normal
(forward) direction.
Oil flow from the gear pump section is sent through the de-energized solenoid
valve S1 to rotate the cooling fan motor. Return flow from the motor re-enters
the manifold (port M2), through the de-energized solenoid valve S1, out of the
manifold (port T) and then is routed through the deck control manifold, oil cooler
and oil filter.
Page 5–41 Hydraulic System: Hydraulic Flow Diagrams