Page 473 - Mechatronics with Experiments

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JWST499-c07
JWST499-Cetinkunt
ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 459
To load
Directional A High pressure
control valve
A B
P = P B
A
A A
Pump (low p)

B Low pressure

FIGURE 7.42: Pressure intensifier circuit.

Notice that the intensified pressure in the forward cycle of the cylinder is equal to the area
ratios between the cylinder head-end and the intensifier ram (i.e., 10),
p A A B
= (7.147)
p A
B A
During the forward stroke, the pressure in chamber A is amplified by the area ratios defined
by the above equation. During the retraction stroke, the intensifier and rod-end of the
cylinder are filled with hydraulic fluid and are not considered a work cycle.

Example Consider a pump that supplies Q = 60 l∕min constant flow to a double acting
p
cylinder. The cylinder bore diameter is d = 6 cm and rod diameter d = 3 cm. Assume the
2
1
rod is extended through both sides of the cylinder. The load connected to the cylinder rod
is F = 10 000 Nt. The flow is directed between the pump and the cylinder by a four way
proportional control valve. Neglect the pressure drop and losses at the valve. Deterimine the
pressure in the cylinder, velocity, and power delivered by the cylinder during the extension
cycle. Assuming 80% overall pump efficiency, determine the power necessary to drive
the pump.
We need to determine Δp , V, and P for both the extension and retraction cycle. Let
L
us determine the areas of the cylinder.
( )
2
d − d 2 2 (6 − 3 )
2
2
1
2
A = = cm = 19.63 cm 2 (7.148)
c
4 4
= 19.63 × 10 −4 m 2 (7.149)
The pressure during the extension stroke that must be present as differential pressure
between the two sides of the cylinder in order to support the load force,
F =Δp ⋅ A c (7.150)
L
F 10 000
Δp = = (7.151)
L
A c 19.63 × 10 −4
2
6
= 5.09 × 10 N∕m = 5.09 MPa (7.152)
The linear velocity is determined by the conservation of flow,
Q = A ⋅ V (7.153)
c
3
Q 60 l∕min 10 −3 m ∕l ⋅ 1min∕60 s
V = = (7.154)
A 19.63 × 10 −4 m 2
c
= 0.509 m∕s (7.155)