MOBILE TRANSMISSIONS USE A4VG,,DAD WITH A6VM,,DA

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#DA_Hydraulic_Control, Speed Related
In relation to the drive speed, control pressure is applied to the
positioning cylinder of the pump by means of the DA control valve
via a 4/3 way directional valve. Pump displacement is steplessly
variable in each direction of flow. Each direction of flow is assigned
to one of the two solenoids on the directional valve.
Increasing drive speed generates a higher control pressure through
the DA valve.
Increasing control pressure increases the pump displacement.
Dependent upon the pump operating curve, pressure in the high
pressure lines causes the pump to swivel back towards a smaller
displacement.
Increasing operating pressure gives reduced displacement.
A constant torque input to the pump is achieved by this combination
of de-stroking of the pump as the operating pressure increases and
in response to the “pull-down” of the prime mover (leading to a
reduced control pressure).
The least possible pull down leads to optimum usage of the drive
power. This is achieved by “partial inching”. In this form of the control,
the DA valve is mechanically coupled to the accelerator pedal. This
means that on reaching a certain speed (movement of the accelerator
pedal), the control curve is offset parallel to the engine speed curve.
Any additional power requirements, e.g. the service hydraulics, may
lead to engine pull down occuring. This leads to a reduction in control
pressure and therefore pump displacement. The power thus released
is then available to supply that demanded. Automatic power division
and full utilisation of power available is thus achieved for both the
vehicle transmission and the service hydraulics.
In an automative transmission, the DA control valve is used in
conjunction with the directly controlled hydraulic “DA control”.
However, pumps with EP, HW or HD control devices can also be
equipped with a DA control valve. In this way, the automatic
transmission function (speed related high pressure/flow increase with
load limiting control) may be overridden.
The maximum flow will then be determined by the setting of the
relevant control module fitted.
Function and Control of DA Valves
(Unit dimensions see page 32...34)
DA control valve, fixed setting, (2)
#DA Hydraulic Control, Speed Related
Control pressure is generated in relation to drive speed. When
ordering, please state in clear text: Start of control (set at factory).
DA control valve, mechanically adjustable with control
lever (3)
Control pressure is generated in relation to drive speed. When
ordering, please state in clear text: Start of control (set at factory).
Control pressure may be reduced (independently of drive speed) as
required by operation of the control lever (inch function).
Max. adm. operating torque at the control lever ____ Tmax = 4 Nm
Max. angle of lever operation 70°. The position of the lever is optional.
Variation 3L _ operation direction of the control lever anti-clockwise
Variation 3R ____ operation direction of the control lever clockwise
Hydraulic inch valve, (4, 5, 8, 9)
(only for pumps with DA control device)
- for inch function; for use in conjunction with DA control
valve, fixed setting (4, 8) or mechanically adjustable (5, 9)
Model with throttle valve sizes 28, 40, 56, 71
Model with pressure reducing valve sizes 90, 125, 180, 250
Permits the control pressure to be reduced independently of the drive
speed via hydraulic control (port Z).
Master controller as inch valve, (7)
- for inch function; for use in conjuction with DA control
valve, fixed setting
Any reduction of control pressure, independent from the input speed
through the mechanical operation of the master controller.
The master controller is installed separately from the pump (for
instance in the driver’s cabin) connected with the pump by 2 hydraulic
control lines at ports PS and Y.
A suitable master controller is to be ordered separately and is not
included in delivery volume.
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#MOBILE_TRANSMISSIONS