Etesia HYDRO 124D Technical Training Manual page 37

4.3) The drive transmission circuit
All the results are given for operation at max. engine rate (2850 rpm).
The maximum cubic capacity of the axial-piston pump is 20.3 cm3/rev. This pump is coupled
with crankshaft of the diesel engine. From that we can determine the flow:
Max. flow of the drive transmission pump : 58 l/min
The volumetric efficiency of the pump is 96%, that is of 100 litres that pass through the pump, 4
litres are "lost" and return to the tank via the drain. With a flow of 58 litres/minute, this means
2.4 litres/minute return to the tank.
In the same way, the volumetric efficiency of a wheel motor is 90%. Assuming that a wheel
motor receives half the flow of the drive transmission pump (that is 29 litres/minute), this means
about 3 litres/minute per motor return to the tank.
In total, the leakage is estimated at : 2.4 + 3 + 3 = 8.4 litres/minute, that is 14% of the 58
litres/minute
Such a system could not operate without a regular addition of oil. This is done by the charge
pump whose cubic capacity is 6.9 cm3/tr. Hence its flow :
Flow of the charge pump : 20 l/min
The charge pump can compensate for leaks representing 20/58 = 34 % of the max. flow of the
pump.
The external leakage is all the bigger :
- the higher the engine speed
- the higher the pressure on the wheel motor connectors (for example : movement on a slope)
ETESIA sells a manometer kit under the reference number 30075. It includes a manometer
graduated up to 15 bars, another graduated up to 250 bars as well as the couplings allowing the
measurement of all the pressures. The latter can also be used with the MVEHH (Hydro 100).
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