JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV ELECTRIC AND HYBRID VEHICLES Previous Question Paper (December - 2020 - R16)

Assessing vehicle performance requires mathematical modeling of the longitudinal dynamics and power flow. The primary models used are the tractive effort model, the road load model, and the power plant energy consumption model.

1. Tractive Effort Model: This model calculates the force available at the wheels to propel the vehicle. It is defined by the torque produced by the motor or engine, multiplied by the gear ratio and transmission efficiency, divided by the wheel radius:

Where T_m is motor torque, G is gear ratio, η_t is transmission efficiency, and r_w is wheel radius.

2. Road Load Model: This model accounts for the resistive forces opposing vehicle motion. The total road load force F_rl is the sum of aerodynamic drag, rolling resistance, and grade resistance:

Here, ρ is air density, A is frontal area, C_d is drag coefficient, v is velocity, M is vehicle mass, C_r is rolling resistance coefficient, and θ is road gradient.

3. Vehicle Dynamics (Acceleration) Model: By applying Newton's second law, the acceleration a of the vehicle is determined by the difference between tractive effort and road load, accounting for the vehicle mass and rotational inertia factor λ:

4. Energy Consumption Model: This model relates the power required at the wheels to the electrical or fuel energy consumed by the power plant. It incorporates the efficiency maps of the motor/engine and battery/fuel tank:

These models are integrated to simulate vehicle performance metrics such as maximum speed, acceleration time (0-100 km/h), and gradeability, which are critical for evaluating the design feasibility of electric and hybrid vehicles.