They are gradually becoming a more common sight on our roads. Sometimes, they startle pedestrians as they draw near at low speeds and even lower noise. We are talking about electric vehicles, of course: the BMW i3, Nissan Leaf, Renault ZOE, Tesla Model S or hybrid cars in electric mode, for example. Do these vehicles need different lubrication concepts?

New vehicle concepts with old and new lubricant applications.

Many electric vehicles are part of a company fleet, included for reasons of image, economic efficiency or simply out of a genuine belief in electromobility. Anyone who has operated a fully electric car knows that it feels completely different to driving with a combustion engine. The vehicles offer powerful acceleration without any interruption of tractive force, high torque right after starting and pleasantly low noise levels.

This market segment is headed for growth. The pace of growth depends on different factors: price trends, range, charging infrastructure, charging duration and, not least, psychological aspects that influence buying behavior, such as concerns about range. But recent e-car models achieve a range of 400 kilometers, some considerably more, which finally consigns the latter issue to the past. Regardless of the pace at which the European charging infrastructure and availability of rapid-charging options will develop, China – the world’s most important automotive market – is highly likely to remain the main driver of demand for BEV.

Do new vehicle concepts also require new lubrication concepts? Hybrid systems will continue using combustion engines. Considering the lubricants and consumables involved, the lubrication technology remains virtually unchanged. In certain cases, interaction between the different drive systems can result in special lubrication requirements.

In vehicles with a lower cubic capacity and more compact engines, downsizing effects can cause a slight reduction in volume of, for instance, the engine oil. The use of lubricants for mechanical parts will not change. Special non-friction coatings remain highly significant, too. These special coatings optimize the performance of the components to which they are applied (e.g. engine pistons) and allow them to withstand extreme operating conditions, which typically exist inside combustion engines. The smaller size of components in hybrid drives increases the strain on piston aggregates. This will make non- friction coatings even more necessary – have a look at our article “Some like it hot” on page 6 for more details.

Besides the bearing lubrication of the electric motor, even fully battery-operated vehicles* have a lot of mechanical components that need lubrication, including those in the chassis. BECHEM uses a multitude of special lubricants for conventional interior and chassis parts; these will be required just the same in electric cars. Some fields of application will become obsolete, however – the starter and drivetrain, for instance. Touchscreens will inevitably replace some mechanical switches.
Interior actuators, on the other hand, are likely to grows non-essential applications that used to be limited to the luxury range are gradually becoming widespread in lower vehicle classes.

*This report is not concerned with fuel cell vehicles that generate electric energy for their electric motor from a hydrogen tank by means of a chemical process.

Anti-friction coatings, fluids and pastes for noise reduction will become more central.

The lower noise level of electric motors make interfering noises developing due to vibration or stick-slip, e.g. as a result of chassis torsion, more notable. This requires compatible noise insulation media. There may also be demand for special non-friction coating products in this segment. These could be used on the coiled wire of the electric motor in order to dissipate heat. Another potential function of such products is the reduction of friction in plug and clutch systems. Special dispersion coatings could also be applied to the actual plug contacts.

High-voltage technologies in electric vehicles raise further questions for the field of lubricant development. Automotive developers are increasingly shifting their focus to 48-Volt onboard power systems as voltage supplies, as they can power more electric devices in a single vehicle. This requires smaller cable diameters, which reduce the overall weight of the vehicle, just as reduced component sizes do. Experts have emphasized further advantages of this technology: shorter engines without belt drives for aggregates, rapid engine starts, regenerative brakes and “sailing mode”, i.e. driving with the clutch disengaged.

Fully electric vehicles have a voltage of 400 Volt or more. Such drive systems, which include electric motors, high- voltage generators and other vehicle systems, generate considerably more powerful alternating fields than conventional systems or vehicles that do not work with high voltages. In power controllers, which regulate the output of the electric motor, parasitic stray currents can cause electric discharge and send current through anti-friction bearings. The heat generated during such events can lead to discharge craters, selective welds, melting marks as well as oxidation and burning of the lubricant grease. This damages and ultimately destroys the bearing. Anti-friction bearings have extremely narrow lubricating clearance gaps (5–25 μm). The frequent occurrence of flashover voltage between the race and the anti-friction bearings causes long-term damage. At the current state of technology, carbon brushes are used to discharge voltage from the electric motor and, in turn, the anti- friction bearings of the drivetrain. This requires encapsulation: the brushes do not work unless they are dry. The main shaft has a clearance gap of 1–2 mm. Any damage to its bearings will soon render the entire electric motor irreparable.

Inverters currently have a frequency of 8 kHz. Manufacturers are considering other materials that will achieve a considerably higher frequency, which is likely to increase the problem of electric discharge.

Hybrid vehicle. Smaller burner dimensions will increase the strain on piston aggregates. This makes non-friction coatings more significant. Depending on the aggregate, the use of transmission and engine oil will decrease slightly.