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.
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 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.
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
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 simulated route is the same as the route used in the previous scenario 1. The performance of the simplest turbo train
The next running curves well demonstrate the effect of 4 speed gear
transmission. The low power 2M4T turbo train runs all motive DMU very
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.
|DMU 6M||1244.28 kg|
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