Effects of Efficient Greases on the Operating Range of BEVs

The use of lubricating greases in hybrid (HEV) or fully electrified passenger cars (BEV) may have a positive impact on their operating range. Here, Fuchs Schmierstoffe explains the prioritization of individual vehicle components for the topic friction minimization, the advantages of efficient greases as well as the special demands electrified vehicles impose on these automotive fluid class.

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Fuchs Schmierstoffe

In order to be able to classify individual greased components in Battery Electric Vehicles (BEVs) or Hybrid Electric Vehicles (HEVs), Fuchs Schmierstoffe carried out an analysis and assigned priorities based on degrees of efficacy relevance. They are defined by the duration of the power supply to the individual components from the vehicle’s battery. The longer a component taps into the battery energy, the higher the electricity consumption.

An efficient or in other words low friction lubrication can improve the degree of effectiveness, thus reduce the energy demand and therefore make an important contribution to the extension of the vehicle’s operating range. Consequently, components that consume more electricity also have a greater operating range boosting potential as a result of increased efficiency. Three efficiency degree relevant priorities generated by optimized grease lubrication were defined which are presented in the next paragraphs.

First Priority: Drive Train

Components that are either parts of the drive trains or directly connected to it are allocated to drive train priorities. While the vehicle is in operation, they take on the role of constant direct or indirect automotive battery electricity consumers. Among the first priorities considered are for instance the greased bearings in the traction electric motor, the wheel bearings or the joint shafts. The potential energy savings of these components as a result of the increased degree of effectiveness are high, since their operation utilizes the largest share of the battery supplied energy. Consequently, a boost of these component efficiencies has the potential of delivering the largest operating range extension. Currently, the focus in the development of low friction greases is on first priority components.

TABLE 1 Grease applications based on priorities and components (*only relevant for HEVs) (© Fuchs Schmierstoffe)

Second Priority: Permanently Servo-Actuation Supporting Components

The second priority comprises components that also continuously embedded into the operation of the vehicle, while assuming supporting roles only. Among these are, for example, the steering system, the brake booster, or the cooler fan. The optimized degree of effectiveness of these components, which can be achieved if low friction greases are utilized, does not have as strong of an impact on the vehicle’s operating range as a first priority improvement of the drive train. However, these components most certainly offer potentials for energy savings, too.

Third Priority: Temporarily Servo-Actuation Supporting Components

Components that are only used for a limited period of time and thus tap into the vehicle battery’s energy supply merely temporarily, are categorized as third priority components. This category includes, for instance, the parking brake or the seat adjustment. Given that these parts are only temporary electricity consumers, their operating range extension potential is much smaller than that of the other two priorities. Nonetheless, even third priority components do have the capability to have a positive impact on the passenger car’s operating range if efficient greases are used. This objective is primarily attained through synthetic greases, which deliver reduced breakaway and driving torques even in low temperature conditions (up to -40°C) and thus demand a lower electrical deployment output.

Evaluation And Advantages Of Degree Of Effectiveness Relevant Priorities

The described categorization into the three designated priorities translates into a focused evaluation of the lubricant applications in HEVs and BEVs. TABLE 1 allocates the greased automotive components to these three priorities.

The friction minimization of grease lubrications can be achieved through a low base oil viscosity as well as special, optimized thickeners and additive technologies. The reducing friction is of particular importance primarily for the degree-of-effectiveness-relevant first priority components. The vehicle’s electricity consumption can be reduced thanks to the decreased power losses in the drive train, which can also be attributed to the lower friction in these components. Among other things, the coefficient of friction μ describes the interior friction of the lubricant that has a significant impact on the degree of effectiveness of the components in the hydrodynamic lubrication area.

The development of efficient greases mandates the precise measurement of the grease dependent friction in model and component test stands under load conditions that are as actual application proximate as possible. One available option is the so-called Mini Traction Machine (MTM) from PCS Instruments. FIGURE 1 includes the measuring results of an MTM test run and clearly identifies the difference in the friction patterns of a standard and a friction-optimized wheel bearing grease. It is clear that the coefficient of friction of the optimized grease has been reduced by 50 % compared with the standard wheel bearing grease (μ = 0.015 instead of 0.030) and thus a positive influence can be exerted on the efficiency of the component.


2023-02-03