Performance Characterization of Automotive Lubricant Used in Electrical Vehicles and Hybrid Electrical Vehicles

By Raj Shah, Blerim Gashi, Simon C. Tung, Andreas Rosenkranz

Global automotive industries have recently switched their developments trends from powertrain mechanical components into digital electrification components in advanced propulsion vehicles thus creating an innovative technology for propulsion systems such as electric vehicles (EVs) and hybrid electric vehicles (HEVs) [1]. These advanced propulsion systems have significantly improved vehicle fuel efficiency thus minimizing pollution emissions from transportation vehicles. Many EVs and HEVs still have automotive lubricants, such as drivetrain fluids or coolants, which have been integrated with electrification components operating in a wide temperature range and under various operating conditions.

This article aims at summarizing the state-of- the art and future trends in electrification and the required lubricants for advanced Hybrid/EV vehicles. Moreover, different failures modes caused by the electromagnetic and electrostatic effects are addressed. To further understand these phenomena, shaft voltages (the main source of electrical failures) must be studied and evaluated upon. In this paper, the main causes of shaft voltages are divided into 3 parts: the magnetic flux asymmetry, electrostatic effects, and inverter-induced voltage effects.

In an EV/hybrid systems, the automotive driveline fluid or coolant is not in contact with the e-motor, but it still needs to maintain all the traditional driveline fluid properties such as aeration, oxidation, frictional properties and gear/bearing pump wear durability. In order to meet these new requirements for electrification components in hybrid vehicles, fluid formulations must be carefully balanced with the need to optimize driveline performance and protection, particularly in a lower viscosity environment, all of which introduces new requirements for the driveline fluid or coolants considerations for these applications.

The authors have reviewed all current bench tests developed for characterization of electrical and thermal heat transfer properties for automotive lubricants or coolants used in EVs and HEVs. Among those bench tests, several ASTM Test Standard Tests for lubricant properties have been reviewed including the following basic lubricant properties: viscosity, density, thermal conductivity, electrical conductivity, andheat capacity / specific heat. All bench test methods have been summarized in this review paper. In addition, the other industrial standard tests for evaluation of tribological properties of automotive lubricants will be described to supplement their required performance characterization.

At the end of this paper the authors provide an overview of relative compatibility between various interface materials and the required coolant options. The polymer or metal materials interfaced with cooling fluids under the extreme operating conditions must be managing carefully to assess fluid and material interactions at specific temperatures, pressures, and other environmental conditions. Those fluid-material compatibility studies in this review paper can definitely provide helpful solution that is optimized for your requirements in EV/Hybrid thermal management systems.

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The above paper and the information contained therein are solely the work of the authors.