Page 465 - Mechatronics with Experiments

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JWST499-c07
JWST499-Cetinkunt
ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 451
P
P s
t
P
desired

P
P Control desired
c pressure
(a)

Pump outlet pressure P P
s t

Control piston for
swash plate actuation
Swash plate

P
c

P
Piston s

P
t
Slipper Tank pressure

Bias piston for swash plate actuation

Tank
(b)

FIGURE 7.36: Hydraulic circuit diagram for a pressure compensated (pressure controlled)
variable displacement piston type pump using a pressure regulating valve. (a) Symbolic
representation of the pressure control valve. (b) Hydraulic circuit diagram of the pressure
control valve and variable displacement piston pump. The desired pressure setting can either
be adjusted by the screw-spring to a constant value, or through a remote pilot pressure control
mechanism for variable pressure regulation applications.

The flow-pressure curves for a flow compensated pump control look as shown in
(Figure 7.37b). In order to maintain a stable output flow, the mechanical input speed of the
pump may also have to be above a minimum value.
(3) Load compensated (load sensing) pump control: control the pump displacement
such that the difference between the actual pump output pressure and the load pressure is
regulated about a desired differential pressure (Figure 7.38),

cmd = offset + K ⋅ (ΔP cmd − (P − P )) (7.130)
s
L