TotalEnergies last-generation EV Fluids validated under real-life conditions

The new environmental challenges drive industrials to come up with alternatives encouraging the transition towards carbon neutrality. Hence the fast development of hybrid and electric vehicles. This changeover implies specific needs and criteria especially in terms of lubrication and thermal management [1]. Indeed, the EV-fluids need to be durable, dielectric, compatible and thermally stable. Therefore, in 2019 TotalEnergies has launched its brand-new range of EV-fluids for passenger cars meeting those requirements: Quartz EV Fluids [2].

EV-Fluids in the Automotive industry:

While EV-fluids are a completely new concept, testing methods are developed to evaluate their performances and set certain limits. Yet, very few specifications are available within the industry to approve the EV-fluid efficiency and more importantly long-lasting performances. That is precisely why TotalEnergies selected GETEC to carry out one of the first internal trial on EV-fluids under real-life conditions.

The main goal of this fleet campaign is to evaluate the aging behavior of TotalEnergies EV-Fluids during high mileage accumulation set, as a first step, at 100,000km by both corporations. More than that, this project is a unique opportunity to assess the impact of the lubricant on an e-transmission system as well as on electrical and electronic components such as eMotor Copper windings.  

Mileage Accumulation EV Test principle:

Vehicles		Range [km]	E-motor
			Type	Cooling	Power [kW]	Torque [Nm]
4x US EV model	AWD	675	Front: Induction Asynchronous Rear: PMSM	Direct-oil-cooling	357 Front: 137 Rear: 220	659 Front: 219 Rear: 440
4x CN EV model	AWD	600	Front: PMSM Rear: PMSM	Direct-oil-cooling	360 Front: 180 Rear: 180	700 Front: 350 Rear: 350

Table 1: Vehicle parameters

The fleet test has been conducted on two distinct driving cycles with the same profile: one in Europe (Germany) and the other one in Asia (China). In total, 8 vehicles have been selected: 4 are from US electric car manufacturer for the German cycle and 4 from Chinese state-owned electric car manufacturer for the Chinese one. The vehicles were tested on the road at least 6 days a week with two shifts per day and multiple drivers in constant rotation reducing any statistical bias. During the night, vehicles were charged by slow chargers and during the day by fast chargers.

For each group of vehicles, two were equipped with the original manufacturer lubricant and the two others with a lubricant from the Quartz EV Fluid range of TotalEnergies: Quartz EV-Drive MP 3.2, specially designed for electric drive units and having a low viscosity profile (see table below) assuring the repeatability of the protocol.

Parameter	Dexron® VI specs	US EV model*	CN EV model**	TotalEnergies Quartz EV-Drive MP 3.2
Kinematic Viscosity at 100°C [mm²/s]	≤6.4	5.9	5.5**	4.6
Brookfield Viscosity at -40°C [mPa.s]	≤15,000	9,210	≤15,000	5,400

Table 2: Oils physical-chemical properties

*Based on US EPA Certificate of Conformity

**Based on CN EV model Owner's Manual

In order to ensure a relevant monitoring of fluid performances, every 20,000km 30 mL of oil was sampled and analyzed by TotalEnergies.  At the end of the 100,000km accumulation, the electric drive unit (EDU) is entirely dissmantled. In addition to usual signal acquisition, GETEC installed specific sensors on all vehicles to monitor closely mechanical, electrical, and more importantly thermal behavior of the sub-systems of the vehicle (electric powertrain, battery…).

 

Physical-Chemical properties:

Physical-chemical properties of the oil are key and relevant parameters to measure on fresh oil and monitor all along the test (that is precisely why sampling was considered). Oil analysis provides a glimpse inside the electric powertrain to gauge lubricant and component condition without disassembling mechanical parts. In this specific case, determining the condition of oil inside the EDU offers thanks to the frequent sampling, such as metal contents (either coming from additives or wear) and contaminants, is a meaningful tool. Indeed, the idea was here to identify early warning signs of mechanical failure or increased gears or bearings wear.

During the fleet test, TotalEnergies measured many others as part of a full list of physical and chemical properties that must be evaluated. The results presented hereafter are extracted from the full dataset generated and are demonstrating  the technical benefits of optimized EV Fluids for such type of applications.

Using a low-viscosity fluid generally offers low friction coefficient, that is precisely why TotalEnergies chose Quartz EV-Drive MP 3.2 for the very fleet campaign. As shown in the graph below, the tested fluid displays the lowest kinematic viscosity at 100°C and remains stable along the 100,000km compared to the Factory-Fill product.

Figure 1: Evolution of the kinematic viscosity at 100°C for the rear part of US EV model Vehicles with and without TotalEnergies lubricants

The evolution of fluid viscosity is one of the key parameters to be monitored throughout the entire run. This type of low-viscosity fluid represents huge challenges for gears and bearings durability, it is relevant to present it here. Therefore, to check the impact of the fluid on mechanical parts a teardown is realized at the end of the accumulation test conducted by GETEC and the continuous analysis of the oil samples throughout the whole project conducted by TotalEnergies.

Durability:

Long-term reliability of the EDU is highly impacted by the fluid lubricating and cooling performances. Therefore, analyzing both the fluid itself as well as mechanical parts such as gears and bearings is key. The durability of the parts can be assessed through oil analysis by various methods, and here the most relevant method is presented and consists of counting the iron dissolved in the fluid every 20,000km.

 

Figure 2: Evolution of the iron dissolved in the oil (ppm) for the rear part of US EV model Vehicles with and without TotalEnergies lubricants

This graph confirms similar Fe accumulation rates between TotalEnergies EV Fluid and the Factory Fill product, with slight advantage for Quartz EV-Drive MP 3.2 as it led to very low amounts of iron particles at the end of the fleet tests. This is consistent with the pictures below of main mechanical parts subject to wear within the EDU (gears and bearings) and for which, internal & third-party experts validated very low level of wear for both products, after 100,000km accumulated on each vehicle.

Figure 3: Mechanical check of main transmission parts

Material Compatibility:  

The compatibility of the fluid with the materials within the EDU, especially with Copper, is one critical challenge that EV Fluids need to overcome. Hence, the amount of dissolved Copper has been measured each 20,000km to get an insight of the corrosive impact of the fluid itself on the Copper wires).

Figure 4: Evolution of the copper dissolved in the oil (ppm) for the rear part of US EV model Vehicles with and without TotalEnergies lubricants

This graph illustrates the presence of copper in the fluid in the rear axle (which is the main driving axle for the US EV model). The green curve is remarkably low at 100,000km, corresponding to Quartz EV-Drive MP 3.2. This is also consistent with the pictures of electric motors the reader will find below, which show no sign of corrosion on wiring or any damage on insulation materials (papers, coatings…).

Figure 5: Wiring lubricated by TotalEnergies lubricant

That justifies again the performances of the EV-fluid in terms of compatibility, and this cannot be achieved with conventional transmission fluids.

Efficiency:

The Mileage Accumulation program was also the opportunity to evaluate and compare the gain in energy that such specific fluids can bring. Therefore, to gather an indication of the EDU efficiency of CN EV model, GETEC evaluated the accumulated energy in kWh/100km in average during the fleet test. In the case of the CN EV model vehicles, the front axle is the main driving one and it is the part where the gain of energy is noticed with TotalEnergies EV fluid.

Figure 6: Gain in energy on the front axle for CN EV model vehicles*

*Based on the fleet test only

For all driving conditions the vehicles with TotalEnergies oil have shown a lower energy consumption compared to the vehicles filled with the manufacturer lubricant. Yet, the results are missing precision with the fleet test hence the realization of an efficiency test following CLTC (China Light Duty Vehicle Test Cycle) using the same EDU which highlights a similar tendency as in the fleet test with 0.382Wh saved with the Quartz-EV Drive MP 3.2 over original manufacturer lubricant.

Conclusion:

It has been shown, thanks to this study, that lowering viscosity for the next generation of fluids for Electric Vehicles can be achieved without compromise on component durability (despite the multiple challenges such as the risk of thin lubricating oil film). TotalEnergies Quartz EV-Drive MP 3.2 has demonstrated very stable performances over the 100,000km test and can be considered as “fit-for-use”, at the same level as original manufacturer oil on both German & Chinese electric cars and cycles. Having low viscosity profile induces lower resistance to flow and exhibition of low internal friction, which is beneficial for energy efficiency that-is-to-say increased ranges for the electric cars. Besides that, viscosity is one of the main contributors for enhanced thermal properties which will be critical for electric machine heat removal.

On top of that, TotalEnergies conducted a thorough optimization of Quartz EV-Drive MP 3.2 technology which went beyond viscosity decrease. The whole additive systems have been designed to offer best-in-class Copper corrosion and oxidation control performances with optimized dielectric and thermal properties.