In this paper, a software framework is presented through an application that is able to jointly optimize an electric motor and a gearbox for the design of a drive system for electric vehicles. The framework employs a global optimization method and uses both analytical and finite element method (FEM) models to evaluate the objective functions. The optimization process is supported by a statistical surrogate model, which allows a large reduction of runtime. An earlier version of this framework was only suitable for electric motor optimization. In the application presented in a previous paper, the motor of a belt-driven electric drive system was optimized. In this paper, the optimization of the same drive system is shown, but now with a combined optimization of a gear drive and motor. The objective functions of optimization are minimizing the total loss energy and the weight of the drive system. The optimization results are compared with previous results to demonstrate the further potential of joint optimization.

Earlier, I created a mathematical model of the gear unit, in which the value of the tooth friction was determined during precalculation and then entered into the model as a constant parameter. In this paper, I investigate how much viscosity oil is required at different operating points for a single-stage gear unit with plastic gears to function properly and how this affects the tooth friction and, hence, the loss of energy in the gear unit. Once the investigations are complete, the tooth friction is determined using an automated MATLAB function, which allows the tooth friction to be re-determined at each operating point. This allows for a more accurate strength dimensioning of the plastic gears in the gear unit and a more accurate model describing the gear unit’s behaviour.

In the case of electric vehicles, due to the favorable torque-speed characteristics of the electric motors used to drive the vehicle, the traditional multi-stage gearboxes common in the automotive industry can be omitted, and in many cases it is sufficient to use a single-stage constant ratio gear unit. Different types of gear units are used for vehicles with different performance levels. In the case of low-performance electric vehicles, a typical solution is to drive only one wheel of the vehicle, e.g., electric motors, bicycles, tricycles, electric racing cars, and mopeds. In this case, a typical solution is to use traction drives. Traction drives can be used as the main drive. This article focuses on the creation of a mathematical model for the energetic modeling of electric vehicles built with chain drives among traction drives. The study examines the possibility of supplementing the electric motor drive of the vehicle with a chain drive, assuming that such a supplement can reduce the energy consumption of the vehicle. With the help of the created model, the chain drive can later be integrated into a complex vehicle model at the design level, and thus the vehicle’s drivetrain can be examined from an energetic perspective in the design phase.

The difficulty in designing gears to be installed in electric vehicles is caused by the fact that the efficiency of gears is generally treated as a constant value in the entire operating range, while these show significant differences in different operating ranges; therefore, it is necessary to examine the energy and efficiency of the gear, and to create a mathematical model, which can be optimally fitted into the vehicle’s drivetrain in terms of energy. I have performed this modeling in previous years for a single-stage gear unit. However, this model encounters physical limitations, since a larger gear ratio modification cannot be performed in one stage; the number of stages must be increased as the gear ratio increases. As the number of stages increases, the structure of the mathematical model changes, as changes to the gear unit must be incorporated into the model. In this article, an extension of the mathematical model of the gear unit is presented.