Feedback-controlled adjustment:
According to the specification above, only those adjustment processes in which the output variable is the control variable (b) are feedback-controlled.
For hydraulic pumps it comprises the pressure reduction and delivery flow control, where it measures a flow rate. It can then take place using a sensor (e.g. flow rate measurement) or the rotation speed of the consumer. The pressure/flow control can be assigned here, but not the "power control", which is only a power limiter.
For hydraulic motors, there is a feedback-controlled adjustment if the speed or the torque is determined and fed back. Therefore the secondary feedback control uses this term correctly, while the secondary adjustment is a control.
Figure V 22: Order of adjustment possibilities for displacement machines
Figure V 23: Controlled adjustment with an internal control circuit (a) and controlled adjustment (b)
Preliminary note :
The traditional language of hydraulic engineers takes particularly little notice of the difference between control and . Therefore, adjustment processes frequently involve talk of "controls" which are actually "feedback controls" Equally "controlling" should not be equated to "adjusting", as this is a measure of the pump, which is necessary for controls and feedback controls. This is taken from an order in accordance with (Figure V 22).
The term "feedback controlling" is only correctly applied to adjustment processes if it relates to output variables of displacement units (pressure and flow rate in pumps and moments and rotation speeds in motors).
If, however, only the travel distance of the adjustment equipment or the pivoting angle of the pump is feedback controlled, there is an internal with the position-controlled setting piston, whereas the output variable of the pump or motor is still subject to interference, e.g. leakage losses - and is therefore controlled.
In practice, this method of observation does not correspond to the standard terms, but it is necessary, as otherwise in light of the increasing use of actual feedback controls in hydraulic systems this would raise false expectations in the case of a "controlled" pump.
Controlled adjustment:
Here a distinction must be made between adjustments with and without an internal control circuit. The latter work only with a control over the entire subsystem (these are still predominant today), while in the case of adjustment using an internal control circuit, a variable (normally the travel distance) is treated as a control variable i.e. here there is a controlled adjustment with a positioned controlled adjustment travel (Figure V 23 a).
It allows a more accurate and reproducible adjustment.
The adjustment process can be performed in different ways:
- mechanically using a hand lever, spindle, cam disc, etc. ,
- electrically using an electric motor,
- or hydraulically (by far the most common group). It is pressure-controlled or travel-controlled with or without a cam disc. Volume-controlled adjustment no longer plays a role;
- electro-hydraulic adjustment with proportional valve or servo valve.
For hydraulic motors there is also the option of
- rotation speed-dependent and
- torque-dependent activation of the set piston.