Section E - Hydraulics
Operation Description
Transmission Pump Operation - Series 2 Machines
E-21 E-21
9803-9340-8
Charge Pump
The charge (or boost) pump 8 is a gear pump which
provides the control pressure for the internal pump control
circuits.
Filtration is provided in the charge pump circuit by an
external filter F.
Displacement Angle (DA) Control Valve
Control pressure is applied to the swash control piston 2 by
means of the DA control valve via solenoid operated
directional control valve 3. Pump displacement is
steplessly variable in each direction of flow. Each direction
of flow is assigned to one of the two solenoids 3a or 3b.
Increasing drive speed generates a higher control
pressure through the DA valve, which in turn increases the
pump displacement.
Pressure in the high pressure lines causes the pump to
swivel back towards a smaller displacement, i.e.
increasing operating pressure gives reduced
displacement.
Any additional power requirements, e.g. the service
hydraulics, may lead to engine ‘pull down’ occurring. This
leads to a reduction in control pressure and therefore
pump displacement. The power thus released is then
available to supply that demand.
Automatic power division and full utilisation of power
available is thus achieved for both the transmission and
the service hydraulics.
Swash Control Piston
Pilot pressure oil causes movement of the control piston 2,
which is directly linked to the swash plate. Changes of pilot
pressure thus cause corresponding changes in swash
angle.
429520-C1
Fig 14.
429530-C1
Fig 15.
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