Freudenberg Sealing Technologies is developing a new generation of conductive sealing materials to make the electrical connection between the housing and shaft of the power transmission system permanent and stable, and to prevent bearing damage caused by electricity and electromagnetic radiation.
Under many operating conditions, the shaft and housing in the electric drive system are electrically insulated by the lubricating film in the contact area of the bearing and shaft seal. In order to keep the system working for a long time, it is necessary to maintain lubrication. The alternating current and its electromagnetic field change the electric potential between the rotor and the stator, so that the rotor is charged. Current can only be discharged from the drive shaft through the grounding system. If there is no grounding channel, current will flow to the bearing with the least resistance. When the current flows from the inner ring of the bearing to the outer ring, an instantaneous large current will be generated, resulting in surface burns and material damage, causing permanent damage to the system. At this time, in order to prevent the power system from malfunctioning, the bearings must be replaced. If you want to easily avoid the current impact, it is necessary to form a durable and reliable electrical contact between the shaft and the housing, to promote the continuous flow of current, to prevent excessive accumulation and sudden discharge.
The huge challenge facing R & D personnel is to find suitable system components to conduct current through continuous contact between the housing and the shaft. Generally speaking, seals are made of insulating materials and are not suitable for this purpose. For many years, Freudenberg has been producing conductive non-woven discs. The disk is tightly connected to the shaft sealing ring, requiring little additional installation space. The conductivity of the nonwoven fabric is realized by special fibers embedded in the matrix. This component can effectively prevent bearing damage and has been used in electric vehicles for many years. With this method, the resistance will be at a very low level.
In the future power transmission system, the power density will continue to increase, making current, voltage and destructive electromagnetic fields continue to increase. To provide a reliable solution, the company is developing a new generation of conductive seals. The first proven functional model will be available in a few months. Dr. Tim Leichner, head of strategic product development at Freudenberg, said: "Our goal is to achieve a constant resistance value over a long period of operation, even under adverse conditions."
In order to meet the new sealing requirements of electric drive systems, Freudenberg has developed suitable test procedures to evaluate and compare the functions of current-loss components. Test bench tests show that in actual dynamic use, static measurements of component resistance cannot predict conductivity. Therefore, German development engineers have developed a dynamic test program that can provide AC current according to the frequency of the car.
It is worth mentioning that the exit point of the shaft at the housing is usually a position that is difficult to "seepage-proof". At this position of each motor, there is a shaft seal, which is conducive to shielding. In this way, the oil and other media can be sealed and combined to resist electromagnetic radiation without adding another layer of non-woven fabric. Francois Colineau, head of product development at Freudenberg, said: "High conductivity helps shield destructive electromagnetic radiation. We may produce more conductive seals."