Page 71 - ATZ11 November 2019 Professional

1 INTRODUCTION AND BASICS To determine the efficiency of a gearbox, speed and torque have
2 MODULAR EFFICIENCY TEST SYSTEM FOR SMALL GEARBOXES to be measured at the input and the output shaft. This can be
3 ADJUSTMENT CONCEPT done with integrated speed and torque sensors. A drive motor and
4 MEASUREMENT DEVIATION AND CALIBRATION CONCEPT a brake are also required to generate a power flow. In order to
5 EFFICIENCY MEASUREMENTS approach operating points, it makes sense to control the motor
6 SUMMARY speed and braking torque. If the test setup is extended by a mea-
suring amplifier and a measurement data acquisition, the arrange-
ment shown in FIGURE 1 will result.

2 MODULAR EFFICIENCY TEST SYSTEM
FOR SMALL GEARBOXES
An essential objective of modular test systems is the possibility of
easy interchangeability of the main components and the associ-
ated high flexibility in the redesign of the test setup. This means
that a wide variety of gear types and arrangements can be tested
by using the same cost-intensive components.
With regard to efficiency tests, this means that it is useful to
use a standardized measuring sliding carrier to connect the input
and output shafts of the test gearbox. The combination of the
measuring sliding carrier concept, FIGURE 2, with a universal mea-
suring amplifier and evaluation software has proved as a very use-
ful solution. This makes it possible to record other parameters,
such as temperature, electrical power consumption, bearing
forces, etc. In combination with thermal isolation, the system
allows to analyse the influence of temperature on efficiency. Fur-
thermore, the modular design can be used to measure the cogging
torque and power characteristic of electric motors. These motor
parameters are needed for the design of the gears. However, expe-
riences with the described system show suitable usage in the
torque range from 0.001 to 25 Nm.

1 INTRODUCTION AND BASICS
3 ADJUSTMENT CONCEPT
The efficiency (η) of a gearbox results from the ratio of the power As FIGURE 1 illustrates, the power flow of the test arrangement
output (P Out ) to the power input (P In ). Further, the power of a rotary starts from the speed-controlled drive unit and goes through the
motion can be described by the product of rotational speed (n) first torque and speed sensor into the gearbox. From the gearbox,
and torque (T), so that the following relationship results: the power flow passes the second torque and speed sensor and
goes to the brake. To avoid the influence of axle misalignment and
P Out 2 ⋅ π ⋅ n Out ⋅ T Out angular error at each interface, compensating couplings of differ-
___
__________
Eq. 1 η = − = −

P In 2 ⋅ π ⋅ n In ⋅ T In ent designs are usually used [1]. If there is an axle misalignment

Adjustable drive Speed and torque sensor Gearbox test specimen

Speed and torque sensor

Measurement data logging Adjustable brake

FIGURE 1 Schematic test setup Measurement data evaluation
to determine the efficiency
of gearboxes
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