DESCRIPTION OF HYDROMATIK A 4 VG..DA/A 6 VM..DA TRANSMISSION UNIT OPERATION
GENERAL By its principle, hydrostatic transmission adapts the torque provided by the IC engine to the wheels according to the resistance encountered by the vehicle and the speed at which the driver wishes to travel. The transmission ratio varies continuously and automatically. The agent enabling the power to be transmitted is mineral oil which is practically incompressible and which is able to withstand substantial loads. The HYDROMATIK A 4 VG..DA/A 6 VM..DA transmission system consists of two separate organs. 1°
An A 4 VG axial piston pump of a plate design, flange-mounted on to the diesel engine and driven directly by the flywheel by means of a flexible coupling.
2°
An A 6 VM hydraulic axial piston motor of bent axis design, flange-mounted on to a coupling case and a transfer case and driving the two axle shafts via a differential.
The pump and the hydraulic motor are linked together by a series of hoses, as are various accessories required for operation of the system: reservoir, filter, drain return to the cooler, etc. The pump absorbs the maximum power supplied by the IC engine and converts it into hydraulic power (product of the pressure generated and the delivery rate). The hydraulic motor receives the hydraulic power and absorbs it completely. The output shaft is then given a torque and speed which is transferred to the axle and distributed to the wheels. The variation in the transmission ratio is obtained by the variation in the displacement of the pump and the hydraulic motor. The pilot pressure acts against the high pressure on the servo positioner in a set ratio (1/3). The preponderance of one in relation to the other determines whether the motor is controlled or not. The minimum motor displacement is limited by a butt screw. A control system sets the motor switching time.
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