Page 457 - Mechatronics with Experiments

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JWST499-Cetinkunt
JWST499-c07
ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 443
Cylindrical
Swashplate Port
Shoeplate barrel plate
Shaft
hole
Piston Shoeplate Shaft Outlet
shoe Piston bias spring Inlet
port port
Pump function Motor function
Swashplate
Port B angle Port B
Outlet
Outlet w out w out
Inlet
Inlet
Port A Port A
(a) (d)
Swashplate
Port B angle Port B

Inlet Inlet
w out w out

Outlet Outlet
Port A Port A
(b) (e)
Swashplate
Port B angle Port B

Inlet Inlet
w out w out
Outlet
Outlet
Port A Port A
(c) (f)
FIGURE 7.32: Axial piston pump and motor: components and operating principles. (a)
unidirectional pump function, (a) and (b) over-center controlled pump functionality, (a) and (c)
bidirectional pump functionality, (d) unidirectional motor function, (d) and (e) over-center
contolled motor functionality, (d) and (f) bidirectional motor functionality.

provide output shaft rotation in either direction. Over-center control allows the motor output
speed direction to be changed even though the input flow direction does not change.

7.3.2 Pump Performance

A variable displacement pump provides the most flexibility, but with additional control
complexity. In this case, the input speed of the pump can be left to be determined by
other conditions (i.e., operator may control engine speed for other considerations, such
as vehicle travel speed), and the desired pump output is controlled by manipulating the
swash-plate angle. The swash-plate actuation logic may be based on regulating the flow
rate, output pressure, or other variables of interest (Figure 7.33). Figure 7.34 shows the
typical steady-state performance characteristics of a pump in terms of its size and efficiency.