DRESSTA TD-25M EXTRA, Service Manual

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HYDRAULICS
SECTION 10
Page 7
DRESSTA TD-25M EXTRA
GENERAL
Fig. 10.4. Fan Drive Pump with Control Module (2)
Location
Fig. 10.5. Fan Hydraulic Motor
8. Electro-hydraulic Pressure Control Module
9. Proportional Valve Solenoid
11. Pump Control Cylinder Piston
12. Axial Piston Variable Pump
13. Torque Converter 3. Fan Hydraulic Motor
14. Fan (see SECTION 6)
At engine start-up, solenoid (9) of pump control module (8) is energized through the engine
electronic control module (ECM). At this moment fan hydraulic motor (3) drives the fan with
minimum rotating speed. In case any temperature raises in one of following systems: drive train
system, engine cooling system or engine charge air system, the temperature sensors placed in
respective system lines send the signals to the engine ECM. Next, the engine ECM generates and
send the control signal to the control module solenoid (9).
The control module solenoid (9) controls the variable pressure valve (10). The pressure valve (10)
actuates pump cylinder piston (11). Pump (12) varies oil flow rate passing to the hydraulic motor
(3), which drives the fan (14) from minimum to maximum speed range (refer to SPECIFICATION in
this Section).
The fan drive pump output pressure depends on the current intensity to the control module
solenoid (9). If pump pressure drops below actual pressure, the pump will try to increase its
displacement, hence the flow, to satisfy fan drive system demand. If the pressure reaches this
pressure, the pump will adjust its displacement to the required system flow (no excess).
With the inverse proportional control maximum pump pressure level will go to standby at maximum
solenoid current, and to maximum pressure at zero current (failsafe in case ECM failure).
Overriding the current signal is an adjustable hydromechanical setting of maximum pressure.
For detailed description of the fan electrical control refer to Paragraph 3, MACHINE ELECTRICAL
SYSTEM in SECTION 8, ELECTRICAL.