A lumped-parameter thermal network model, based on the analogy between heat transfer and electric current flow, is presented for hybrid powertrain cooling systems. In order to optimally select the powertrain components that are commercially viable and meet performance, emission, fuel economy and life targets, it is necessary to consider the influence of cooling architecture. Especially in electric and hybrid vehicles, temperature monitoring is important to increase power and torque utilization while preventing thermal damages. Detailed thermal models such as FEA and CFD are considered for component level assessments as they can locate thermal hotspots and identify possible design changes needed. However, for the system level analysis, the detailed numerical models are not suitable due to the requirement of high computation effort. Gray-box modelling technique which is a combination of data driven and physics-based models can be employed to estimate heat rejection from each component and average component temperatures for cooling system design. After preparing the physics based thermal network model, the coefficients are derived based on the temperature readings from test/simulation. Co-simulation of the thermal model with powertrain components can achieve the synergistic optimal solution.
In this paper, a mathematical thermal model of a range extender vehicle cooling system with multiple cooling loops for engine, generator, traction motor, and battery is presented. Thermal inertia of the powertrain components and convective heat transfer to the coolant are defined using equivalent capacitance and resistances, respectively. The energy equations are solved in state space form to calculate component temperatures. This approach reduces simulation setup time and computational effort, approximately 100 times, compared to commercially available 1D simulation tools with an estimated temperature difference of less than 2%. The presented modelling approach is ideal for system level entitlement studies.