Atlas Copco air motors - IAG

Torque
[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
Torque
[Nm]
50 100
Speed [100%]
Torque
[100%]
100
Speed [r/min]
Figure 1
10 50 100
Speed [100%]
LZB LZL
6 ATLAS COPCO AIRMOTORS
50
20
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.
Torque
[Nm]
Stall
torque
Min
starting
torque
The use of gear units
Torque
Power
Speed [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.
Torque
[Nm]
4:1
2:1
1:1, 2:1, 4:1 = gear ratios
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
Torque
Power
Speed [r/min]
Figure 4