A Mankato-based company that has been family owned since it was created 55 years ago has been sold to a German company.

The owners of Katolight, Kay and Lyle Jacobson, made the formal announcement Tuesday that the business, which builds generator sets to supply power for large buildings and for various portable needs, has been sold to Tognum, a worldwide supplier of diesel engines based in Friedrichshafen, Germany.

Both parties have agreed to not disclose any details about the price paid for the company, which employs about 360 people at multiple Mankato facilities.

Katolight was spun off of Kato Engineering by Cecil Jones, Kay’s father, in 1952. Jones had already built Kato Engineering into a large generator building company that flourished during World War II. That company was sold to Reliance Electric in 1978 and has been owned by Emerson Electric since 1999.

There has been rapid growth at Katolight during the past four years. Its revenues have expanded from about $59 million in revenues four years ago to about $140 million last year. The number of employees at the business has more than tripled from less than 100 a decade ago.

Tognum executives including Armin Groeber, the company’s new chief executive officer, said they expect the business to continue expanding rapidly in Mankato as its existing generator set business is moved to the Katolight location. Tognum also is looking at ways to build generator sets that use renewable fuels such as soy diesel and synthetic soy diesel.

“I hope that in the next 12 months or 18 months down the road we’ll have some good stories to share,” said Christof von Branconi, Tognum executive vice president.