Page 459 - Mechatronics with Experiments

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JWST499-Cetinkunt
JWST499-c07
ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 445
The primary performance measures of a pump are specified by the following
parameters:
3
1. displacement in in ∕rev which defines the size of the pump, D ( ),
p
2. rated flow, Q , at rated speed and rated pressure,
r
3. rated pressure, p ,
r
4. rated power (derived quantity from rated pressure and rated flow),
5. dynamic response bandwidth of the pump displacement control system if the pump
is the variable displacement type.
The secondary peformance specifications include:

1. efficiency: volumetric, mechanical, and overall,
2. maximum speed,
3. weight,
4. noise level,
5. cost.
The volumetric efficiency ( ) refers to the ratio of the output fluid flow to the volumet-
v
ric displacement of the pump. It is a measure of the leakage in the pump. Mechanical
efficiency ( ) refers to the losses due to factors other than leakage, such as friction and
m
mechanical losses. The overall efficiency ( ) refers to the ratio of the output hydraulic
o
power to the input mechanical power of the pump. Let the units of each term be as follows,
2
3
D m ∕rev, w shaft rev∕s, p N∕m . These efficiency measures are functions of the pressure
p
and speed of the pump,
Volume out
= (7.80)
v
Volume
disp
Q out
= (7.81)
D ⋅ w shaft
p
and
Power ∗ out
= (7.82)
m
Power
in
p out ⋅ D ⋅ w shaft
p
= (7.83)
T ⋅ w shaft ⋅ (2 )
p out ⋅ D p
3
= ; for D in units of m ∕rev (7.84)
p
2 T
and
Power out p out ⋅ Q out
= = (7.85)
o
Power in T ⋅ w shaft
= ⋅ (7.86)
v m
3
Notice that if the unit of D is in m ∕rad, then mechanical efficiency would be defined as
p
p out ⋅ D p
3
= ; if D unit is m ∕rad (7.87)
m
p
T
The difference in the definition of the mechanical and overall efficiency is the definition
of output power. The mechanical efficiency defines the output power as the power if there