Rivian has devised a way to cool electric motors to ensure consistent performance and longevity.
In its quest for optimized EV efficiency, Rivian has created a way to control the heat load in critical areas of electric motors. According to a patent discovered by CarBuzz at the United States Patent and Trademark Office (USPTO), this new Rivian motor cooling system promises more-consistent performance and improved reliability for future versions of the R1S and R1T.
Battery packs have fairly well-developed temperature management systems. Because battery range drops at low temperatures and batteries can chemically degrade at high temperatures, systems are in place to keep battery core temperatures around 25 degrees Celsius (77 degrees Fahrenheit). This is close to the optimal battery temperature for the best blend of efficiency and durability and is usually achieved using fluid-based closed cooling systems.
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Electric motors also work best within a prescribed temperature range but are particularly sensitive to high temperatures. Simplicity is often cited as a major advantage of electric motors, mainly because they don't need pressurized lubrication, but their sensitivity to heat control needs to be managed.
This means that battery and motor cooling must be kept separate, as the two component sets have different temperature tolerances. There are some difficulties with introducing conventional temperature management systems to electric motors, however, with the intricacy and density of their winding construction being one of the major obstacles. Existing methods do go some way to addressing the challenge.
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Current standard practice regarding EV motor cooling mainly concentrates on cold base plate cooling, where the electric motor is mounted on a cooled base plate (heat sink). Air cooling is another option, but when the electric motors become very powerful, it becomes near-impossible to shed enough heat to keep the motors working at their peak efficiency. As another example, Tesla uses its transmission and reduction gear oil to extract heat from the motor's stator (the part with the electrical windings that makes it work), but this is also a design compromise.
Conventional closed-circuit cooling of an electric motor is difficult to achieve, partly because coolant flow through the dense windings is challenging to manage. And, unlike a battery pack, moving components in an electric motor could cause sealing issues and more complex construction.
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The new Rivian patent proposes using coolant sprayers on the outer stator windings to solve this problem. The coolant can be an oil-based electric motor lubricant or a special dielectric (insulating) fluid derived from purified synthetic oil. Spraying the stator windings with this coolant drenches the windings with this coolant.
An oil sump will catch the coolant after it has passed through the windings, from where it will be pumped to a heat exchanger to shed the absorbed heat before being returned to the stator windings via an electronically-controlled pump. Electronic control enables more accurate management of the motor's temperature and will ensure more consistent performance, as well as reduce the risk of thermal shock damage to the stator coils. The end result is a longer motor life as well as consistent performance, regardless of how hard the electric motor has been working.
Perhaps these updates will come to new versions of the company's existing products, or maybe they'll only be seen in a few years to come. If EVs are to take over, they need to get more efficient, and Rivian is working overtime to make that happen.
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Keyword: Rivian Knows How To Make Electric Motors More Reliable