Atlas Copco Air Motors

Par
[100%]
100
Introducing the air
motor
The air motor is one of the toughest and most
versatile power units available to today´s
design engineer. It is easy to control over a
wide speed range, and it produces maximum
torque where it is often most needed – at start
up.
The performance of an air motor is dependant on the inlet
pressure. At a constant inlet pressure, ungoverned air
motors exhibit the characteristic linear output torque/speed
relationship. Figure 1.
However, by simply regulating the air supply, using the
techniques of throttling or pressure regulation, the output of
an air motor can be easily modified.
The free speed and torque can be regulated down to 50%
for an LZB air motor. The free speed for an LZL can be regulated
down to 10% and the torque can be regulated down to
20%. The shaded areas in figure 2 illustrate this.
50
Par
[Nm]
50 100
Velocidad [100%]
Par
[100%]
100
Velocidad [r/min]
10 50 100
Velocidad [100%]
LZB LZL
6 AT L A S C O P C O A I R M O T O R S
50
20
Figure 1
Figure 2
It should be noted that all vane air motors produce a variable
starting torque, due to the position of the vanes in the motor
when it is started. The variation differs between motor types
and must be checked on an individual basis.
The power that an air motor produces is a function of torque
and speed. All ungoverned air motors produce the same characteristic
power curve, with maximum power occurring at
around 50% of the free speed. The torque produced at this
point is often referred to as ”torque at maximum output.”
The performance curves for an ungoverned air motor operating
at a constant air pressure are illustrated in figure 3.
Par
[Nm]
Par de
ahogo
Par de
arranque
mín.
The use of gear units
Par
Potencia
Velocidad [r/min]
Figure 3
Air motors operate at high speed and, although they can be
controlled over a wide speed range, the output characteristics
are not always suitable for the application. To achieve the
required output an appropriate gear unit can be selected. The
ability to change the output by use of a gear unit is illustrated
in figure 4.
Par
[Nm]
4:1
2:1
The planetary and helical gear units used by Atlas Copco
have a high level of efficiency that can be assumed to be
100%. The power output remains virtually unchanged also
when gears are used.
Note. The above does not apply to worm drive gear units, which can have
high frictional losses and, therefore, loss of power output.
1:1
Par
Potencia
1:1, 2:1, 4:1 = relaciones de engrane
Velocidad [r/min]
Figure 4