Computer Aided Match Method for Matching the Electrical Motor and the Gearbox of the Pure Electrical Vehicle - Advanced Research on Computer Education, Simulation and Modeling - page 12

The climbing capacity and the accelerating capacity should be considered while
choosing the maximum ratio. The climbing force that required during the climbing
process is:

F rmax =F f +F imax . (2)

Where, the F f is the roll resistance, the F imax is the gradient resistance.
According equation (2), the required climbing force whose value is 5895.6N is
calculated using MATLAB.
The accelerating resistance during the accelerating process is:

F j = δ mdu/dt . (3)

Where, the δ which equals to 1.35 is the rotating mass conversion coefficient.
According equation (3), the accelerating resistance whose value is 3750N is
calculated using MATLAB.
Then the required maximum driving force is 6600N. So the maximum ratio of the
gearbox is 14 in accordance with the maximum output torque of the motor while the
pedal voltage is the largest which shown in Fig. 6.
Based on the method to drawing the mapping characteristics whose vertical axis is
pedal voltage, the maximum and the minimum ratio designed in the foregoing
paragraphs, the contour which depicts the 80% efficiency area is shown in Fig. 12.

Fig. 12. 80% Efficiency area of two gears Fig. 13. 80% Efficiency area of three gears

It can be seen from Fig. 12, the 80% efficiency area of the minimum ratio and the
80% efficiency area of the maximum ratio does not coincide. So the difference
between the efficiency before shift and the efficiency after shift is large, the economy
of the vehicle is not high using two gears gearbox, the gears should be more.
Then, a three gears gearbox is adopted. The ratio of the middle gears is 6.07 while
the geometric progression is adopted to distribute the ratio of all gears. The contour
which depicts the 80% efficiency area drawn by MATLAB is shown in Fig. 13.
It can be seen, that the 80% efficiency area of the minimum ratio and the 80%
efficiency area of the middle ratio has a large concurrent area, so does the 80%
efficiency area of the middle ratio and the 80% efficiency area of the maximum ratio.
The economy of the vehicle could be increase if the gearbox is shifted in the
concurrent area.