Functional description using the A4VS axial piston pump with HS4 control as example
The swivel angle and pressure control as well as the power limitation of the A4VS… variable displacement pump are realized by an electrically controlled proportional valve (1). Via the actuating piston (2) of the pump, this valve determines the position of the swash plate (3).
If the pump does not rotate, in case of depressurized high pressure and actuating system and if enable is not operated, the swash plate is held in the “Zero” swivel angle position by the spring centering.
The position of the swash plate is determined by an inductive position transducer (4), the actual pressure value is recorded by a pressure transducer. Both actual values are supplied to the VT-VPCD control electronics and linked with each other by the software.
The actual power value is calculated from the product of actual pressure value and actual swivel angle value. The controller software ensures by means of a minimum value generator that the controller corresponding to the working point is always active.
In the static condition (i.e. swivel angle command value equals actual swivel angle value, power command value equals actual power value or pressure command value equals actual pressure value) the valve control spool is in central position.
If the superior controllers demand e.g. an increase in the swivel angle (corresponds to an increase in the flow), the valve control spool must be deflected out of the central position until the swivel angle has reached the required value.
The sectional drawing shows the A4VS… variable displacement pump with HS4 control; the proportional valve (1) is controlled using the VT-VPCD control electronics.
Notice for the HS4 control:
With de-energized proportional valve and pump with clockwise rotation and if the set pressure is available, the pump swivels to swivel angle α = 0 (A4VSO design) or α = –100 % (A4VSG design).