The
transmission test rig is used for performance and endurance
testing of automobile transmission systems.
The transmission unit
in a vehicle acts as a medium for supplying mechanical
power from the prime mover (i.e. engine) to the wheels.
The transmission to be tested is driven by an A.C induction
motor. The transmission is loaded by means of a hydraulic
powerpack, motor and dummy transmission system. Two
such sets are used to load both sides of the axle either
individually or together. The hydraulic powerpack has
control valves provided to control the torque applied
to the axle. The dummy transmission acts as a torque
multiplier. In its absence, a larger hydraulic powerpack
would be required to produce the same braking torque.
The figure given below may be referred .
A computer based data
acquisition and control system is used to gather test
information i.e. oil temperature, output rpm, applied
torque etc. Through this the operator is able to select
various test cycles for performance or endurance testing.
This test data is then used by R&D to calculate
the transmission efficiency and expected life. In the
setup, the induction motor acts as the prime mover to
drive the transmission. Earlier test rigs used either
a diesel engine or D.C motor/drive system as the prime
mover. However, A.C motor/drive systems are slowly replacing
the older systems.
| 1. |
The test requires
the transmission to be run at various speeds from
850 to 2880 rpm. This necessitates use of a variable
speed drive.
|
| 2. |
Speed holding accuracy
of +/- 0.1%. The accuracy of the test results
depends on the drive system maintaining set speeds
under varying load conditions.
|
| 3. |
High dynamic response.
Some tests call for the transmission to be subjected
to fast load changes. This calls for fast acceleration
and deceleration times. Hence dynamic braking
is essential.
|
| 4. |
Control of torque
at the input of the transmission. It is required
that the drive be operated in torque control mode.
This enables the operator to give a predetermined
torque set point and observe how the transmission
under test responds under varying load conditions.
For this the A.C drive needs to be operated in
closed loop vector control with PG feedback. This
control method is also able to achieve better
dynamic response.
|
| 5. |
Connectivity of
the A.C drive to the computer based data acquisition
and control system. This facilitates exchange
of set points and drive parameters between the
two systems.
|
The speed vs torque requirements
could be arrived at as given in following table based
on test requirements (example) :
Much against the tendency
to arrive at the required motor kW rating of motor by
multiplying highest speed and torque figures , good
judgement is required to arrive at the most economical
combination of motor and drive ratings that would serve
the purpose. Motor may have to be force ventilated and
drive may have to be operated in flux weakened mode
beyond base speed.
L&T Automation has
got good experience in meeting end-user requirements
by proper application engineering.
