Week 7 Challenge

VEHICLE BODY

The vehicle body is the part where all the forces acts on the vehicle except some inertial force. The modelling of the vehicle body is thus essential part of vehicle design. The various forces acting on the vehicle body are rolling resistance force, air drag, grading force, etc. These forces are all acting on the vehicle body as the vehicle body are in direct contact with the environment. The vehicle body considers all the inputs like

• Mass of the vehicle and payload (`M`), frontal area of vehicle (`A_f`).
• Environment factors like air density(`rho`), wind speed, grade of road (`alpha`)etc.
• Vehicle details like coefficient of drag(`mu_(rr)`), coefficent of rolling resistance (`C_d`) etc.

By considering all the vehicle body is modelled as shown below.

The variables used in the model are stored in init files.

The model calculates the total effective force (= traction force - total force acting on vehicle), then its divided by mass of the vehicle (kerb+payload) to give acceleration of the vehicle as output. The acceleration is integrated to give velocity as the output.

The model also calculates the various force like

Rolling resistance force: force due to friction between the tire and road

`F_(rr) = muMgCos(alpha)`

Air drag: force due to air density and wind speed + vehicle speed (V)

`F_(ad) = frac(1)(2)rhoA_(f)C_(d)V^(2)`

Grade: The force due to grade of road and mass of the vehicle

`F_g = MgSin(alpha)`

To analyse the performance of the model, a drive cycle is required to create. These can be created using a signal builder, follow the steps

1. Open signal builder.
2. Change the time range to 600s
3. Next create a new custom signal. Enter "t_cyc" for time and "v_cyc" for y limit.
4. Click ok to generate the signal.

The genrated signal is as follows

For analysing the result we are giving this input to the forces acting on the vehicle. The result of total force acting on the vehicle are

OBSERVATION:

• The rolling resistance is constant and becomes zero when the vehicle is stoppped.
• The air drag force on the vehicle is more compared to rolling resistance force, the force is proportional to the square of velocity. The velocity is time changing and thus force also changes with respect to velocity.
• The grade is zero, so that the grade force is zero.
• The total force acting on the vehicle is sum of air drag and rolling resistance.

The MATLAB model is attached with this: vehicle_model.slx

Init files: US06.mat, VEH_Data.mat, ENV_Data.mat