Seals for Electromobility Applications
HiSpin PDR RT and HiSpin HS40 Rotating Seals
Trelleborg Sealing Solutions Germany, Stuttgart, launches the HiSpin PDR RT and HiSpin HS40, two seals specifically developed for electromobility applications. Engineered to operate at high velocity, they make a significant step in overcoming issues related to sealing at high rotary speeds that limit electric cars being able to meet the ultimate goal of travelling the same distance as a gasoline vehicle on one charge, according to the company.
A major technology in electric vehicles is the e-axle, a combined electric motor and gearbox that fits within the traditional engine space. The motor and gearbox are directly coupled but while the gearbox requires efficient lubrication, it is essential that the motor remains dry and so a highly reliable seal is required between these two components.
Gasoline engines normally run at 2000 to 4000 RPM but the electrically driven transmission runs up to eight times faster typically at 16,000 RPM and in the future this is likely to increase significantly.
The rotational surface speed limit for traditional seals in the e-axle of today’s electric cars is around 30 m per second. The theoretical optimum rotational surface speed of the e-axle would be greater than 60 m per second to maximize efficiency, a speed that is currently impossible to achieve, according to the company.
Another issue that had to be overcome is the lack of lubrication in the system. In the gearbox side of the electric drive system, lubrication can be very limited; there is usually just a mist of lubricant. When there is little or no lubrication, sealing is more challenging. In these conditions rotating seals will be subject to high frictional forces and stick-slip after periods of rest, potentially causing wear and shortening the life of a seal, as well as power loss, lowering the travelling range of the vehicle.
Diversity of lubricants in the electric drive system is also a difficulty and not all sealing materials are compatible with or operate effectively in the media involved. In addition, the trends in lubricants used could bring up unknown challenges when water-based, dielectric and lower viscosity media come into play.
The result of the development program was two solutions that are being launched together as HiSpin PDR RT and HiSpin HS40. They both have the same function but dependent on the operating parameters of the electric drive system and the customers’ preferences, one is likely to suit a system better than the other.
HiSpin PDR RT is constructed from two parts: a precision manufactured metal body and a mechanically retained polytetrafluoroethylene (PTFE) sealing element. It has a custom designed lip with additional features that improve performance and behavior of lip laydown profile on shaft, crimped into a precision-machined body.
Capable of speeds of 60 m per second and beyond, it has both high and low temperature capability. Able to handle pressure, it is universally compatible with chemicals and its low friction coefficient means it is capable of dry running. Prototypes are offered through a recently launched Rapid Prototype Service introduced to support customers. A conductive PTFE based grade is available.
With a unique bi-directional hydrodynamic lip feature HiSpin HS40 has negligible frictional torque at high speeds. As a result of extensive FEA studies, its rubber lip geometry and flexible design give optimum lip contact on the shaft, ensuring optimum static and dynamic sealing performance.
Trelleborg Sealing Solutions Germany GmbH
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