powertrain models
An effective approach for powertrain modelling is to break the full system down two sub-systems; electrical and mechanical.
Electrical Sub-System
The electrical sub-system generally consists of a power convertor, battery, electric motor and controllers for each of these components. One of the most used motors for an EV is the AC Permanent Synchronous Magnets Motor (PMSM) due to its enhanced performance through superior acceleration and torque capability. The power convertor is made up of a DC-DC convertor and an inverter. A DC-DC convertor adapts the voltage of a direct current to a suitable power level for another component within the powertrain, maintaining the current type. The inverter is responsible for supplying the PMSM with 3-phase AC-power, by converting the DC power from the battery into AC.
Mechanical Sub-System
The mechanical sub-system consists of the gearbox, differential, the axle shaft and the wheels. This is connected to the electrical sub-system through the motor clutch, responsible for engaging and disengaging the PMSM with the gearbox. Each of these components takes into account torque, moment of inertia and rotational velocity with the gearbox and differential also being effected by the gear ratio and energy transmission efficiency. Overall, the system represents the reduction in torque from PMSM to wheels due to inertia and damping within each of the mechanical components.
Benefits to the eRallyCross project
The eRallyCross team would be able to make key vehicle design choices based off the information provided by the powertrain simulations. Graphs such as axle shaft torque, vehicle tractive force and vehicle vertical force (front and rear) can be produced along an input track. The power consumed by each individual component can be determined assisting with the development of an energy management system. This would also provide the client with a more realistic overview of how the battery will perform throughout a race, being able to analyse where the majority of energy is being consumed and the state of the battery after race completion.