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The electrical-motor
driving system, which has been popular for the engine
cooling fan system, is not adequate for constructing
a cooling fan system of small size and light weight
while achieving a reduced fan noise and a large
air flow. For satisfying these requirements, a new
hydrostatic driving system for cooling fans has
been developed. This system is composed of a hydraulic
pump driven by an engine, a hydraulic motor driving
a cooling fan, a reservoir tank, hoses, and an electronic
control unit. The fan speed is controlled by an
electro-hydraulic pressure control valve in the
hydraulic pump. However, the pressure fluctuation
with extremely large amplitudes and relatively low
frequencies were observed to occur in this hydraulic
system when operated at low oil temperatures.
In this study, the
cause and mechanism of the fluctuation along with
the countermeasures were clarified by utilizing
a simulation analysis technique.
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