Does
the 4 speed transmission improve the performance?
M1 Abrams tank has 4 speed transmission. This
mechanism makes up for the 2 shaft gas turbine's insufficient torque at
the low rpm range for rail applications.
To demonstrate effects of the 4 speed transmission, design turbo
trains with the four-speed gear box. The consist of each train is same
as that of previously designed.
The next is performance curves of them.
The acceleration force at low
speed range dramatically improves and even the 2M4T turbo train achieves
the performance close to the DMU made up of all motive cars.
The performance curve becomes more close to an ideal curve.
The four speed transmission also improves the fuel consumption
because the turbine can spin at the optimal speed by changing gears when the
train is running at the low speed.
The high acceleration reduces the powering time and the optimal engine
operation increases the efficiency. As a result, the total fuel
consumption decreases.
To understand this feature, notchman mini has a good function. It is
generally called the efficiency distribution chart or map. This is a
color coded map of the combined efficiency of the engine and the
drivetrain as a function of the train speed and the output. In this
map, the white parts are most efficient and the black parts are
worst.
The next is the efficiency distribution map of the single speed
direct drive turbo train powered by the simple cycle two-shaft gas turbine. The
high efficiency is available only in the limited area and the lower the speed
and load, the worse the efficiency is. The optimal rpm of the aero-derivative
gas turbine is designed as the maximum rotation speed and if such a engine used
for the vehicle application, the most efficient speed equals to its maximum
speed and in most cases, not suitable from the point of view of fuel
consumption.
As described in the user's manual of notch man mini, the maximum rpm of gas
turbines designed for vehicles was set to 120 to 160 percent higher than its
optimum rpm. AGT1500 can spin 120 percent rpm and Chrysler turbine car had the
engine that could spin 160 percent rpm against its optimum point. This feature
improves performance of the single gear direct drive. The paid version of
notch man mini has the function to simulate this kind but the free version does
not allow it.
On the other hand, diesel engines demonstrate a good efficiency
in the wide area of the speed and the output. The efficiency of the hydraulic
converter is not good enough but after the engine is directly coupled, the
efficiency is high and still maintains high in the area of low rpm and the partial load as
shown below.
The recuperation of the gas turbine improves the
efficiency at the low load of the engine and 4 speed gear box improves
the efficiency at the low speed of the train as shown below.
The next running curves well demonstrate the effect of 4 speed gear
transmission. The low power 2M4T turbo train runs all motive DMU very
close.
The improvement is also seen when the distance between stations is short.
The required time is shown below.
The next table shows the fuel consumption. About 20 % reduction of the fuel
consumption is achieved by 4 speed gear drivetrain.
Consist
single speed
four speed
2M4T
1232.36 kg
1032.76 kg
3M3T
1399.42 kg
1214.03 kg
4M2T
1556.47 kg
1374.14 kg
DMU 6M
1101.54 kg
The traveling time reduction and the fuel savings are simultaneously
achieved. Especially in 2M4T turbo train, the required time is a few minutes
longer than 6M DMU but the fuel consumption is less. This is due to the
turbine's light weight and high accelerating performance..
The next is the simulation result of scenario 2 done in previous page. The
same tendency is seen in this simulation.
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