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Digital closed-loop control electronics for the A4VS... axial piston pumps with HS4 variable displacement and A2V... axial piston pumps with EO4 variable displacement VT-VPCD
Digital closed-loop control electronics for the A4VS... axial piston pumps with HS4 variable displacement and A2V... axial piston pumps with EO4 variable displacement VT-VPCD
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Component series 1X
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Digital, Euro-card format
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For swivel angle and pressure control as well as power limitation of a axial piston variable displacement pump
- Control electronics for adjustment of axial piston pumps A4VS…HS4 (NG40 to NG1000) and A2V…EO4 (NG500 to NG1000)
- Pressure controller with subordinate swivel angle controller
- Parameterizable power limitation
- Leakage compensation
- Master/slave capability
- Mooring capability
- PROFIBUS (optional)
Component series |
1X | ||
Type of electronics |
Digital | ||
Design |
Euro-card format |
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).
Functional description of the control electronics
The control electronics is set-up as printed circuit board, fitted on both sides. It comprises a switching power supply unit [1] creating all internally required voltages.
The central unit is a microcontroller controlling the entire process and realizing the controller functions. Data for configuration, command values and parameters are stored in a FLASH in a non-volatile form.
Four binarily coded digital inputs are used to call up parameter sets (command values) from the memory in which you can store a maximum of 16 sets. A call-up activates a command value for the swivel angle, the pressure and the power limitation as well as ramp times for swivel angle and pressure.
More control inputs have the following functions:
"Command value valid":
Enabling of the parameter set addressed by the current call-up (H active)
"Enable":
Activation of the control (H active)
Please note:
H active = activate at high level
Via the differential inputs AI7, AI5 and AI4 [3], the analog command value presetting for the swivel angle, the pressure and the maximum power are specified. With a positive swivel angle command value, the pump swivels in "counterclockwise" swivel direction (= direction of flow P → B). The digital call-up command values are added to the analog command values; the total of both command values is supplied to the controller input via the relevant ramp generators.
The controller output signal controls the output stage [6] depending on the command/actual value differences.
The position of the valve control spool [11], the swivel angle of the variable displacement pump [12a, 12b or 12c] and the system pressure [13] are measured and supplied to the control loop via evaluation electronics [7].
Modes for pressure control
Depending on the configuration, the pressure controller works with one or two pressure sensors.
Open circuit:
1 sensor, optionally current or voltage
Closed circuit:
2 sensors, optionally current or voltage
In the closed circuit, both pressure sensors are evaluated. As soon as the control electronics is in pressure control, the larger of the two pressures determines the control behavior. To compensate control deviations (pressure command value - actual pressure value), the pressure controller can also swivel the pump to the opposite side as well as beyond its specified swivel angle command value.
The switching outputs are configured via BODAC. The following functions may be selected:
DO1: Swivel angle control active
DO2: Pressure control active
DO3: Power limitation active
DO4 Slave mode active
DO5: Swivel angle in the accuracy window
DO6: Pressure in the accuracy window
DO7: Rectangular 32 Hz
The test output (b26 or measuring socket X1) is also configured via BODAC. It is used for the analog output of internal variables.
Enable and error messages
Setting the enable input activates the control. If no command value call-up is activated, parameter set 0 is set.
Error logics identify the following faults:
Cable break or short-circuit in the actual valve value recording
Cable break or short-circuit in actual swivel angle value acquisition
Cable break at the pressure transducer (only current interface)
Closed-loop errors (i.e. control deviations between swivel angle command value and actual swivel angle value)
An error is indicated at output d22. The "OK" message goes out, signal level is 0 V.
Errors are also shown at the display.
Parameterization and diagnosis
Using the serial interface [2], the pump size is selected and the leakage oil correction and the sequence control are activated or deactivated and switching outputs and the test output are configured via BODAC at the front-side D-Sub socket. Via the local bus, up to 32 control electronics can be connected. Via BODAC, every control electronics is assigned a bus address. Reconnection of the serial interface cable is not required. More information in document 30028-01-B.
[ ] = Assignment to the block diagrams
VT-VPCD control electronics in connection with the axial piston pump A4VS…HS4 or A2V…EO4 serves for realization of all electrical functions required for adjustment. Parameterization is effected via a serial interface.