6Modeling and Analysis of Electric and Hybrid Electric Vehicles' Propulsion and Braking

6.1 Introduction

Propulsion and braking performances, such as maximum speed, accelerating time, gradeability, and stopping distance, are among the most important factors to judge in a car. During designing, analyzing and sizing of vehicle powertrain and braking systems, the calculation of these performances at the early stages of the vehicle development process is essential. For this purpose, it is necessary to develop vehicle dynamics models to address vehicle longitudinal dynamics behavior. Such models are based on the following assumptions:

  • The model should be simple. Simplicity is beneficial as it helps us solve the model analytically, and makes the model an effective design and optimization tool. In this regard, only those degrees of freedom that significantly affect the vehicle's longitudinal dynamics are considered. In addition, it assumed that the vehicle accelerates or brakes during straight line driving.
  • During straight line accelerating or braking, the longitudinal velocity and the wheels' angular velocities are the most effective degrees of freedom. As such, the model's degrees of freedom are selected from these.
  • The model does not consider the lateral motion, yaw, roll, pitch, and vertical motions; as their effects on longitudinal motion are negligible.
  • While accelerating on dry roads, longitudinal wheel slips are small, however, during braking; the wheel slip is no longer ...

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