BERLIN (Reuters) - Audi has appointed the research and development (R&D) chief of Swedish carmaker Volvo as its new head of technical development, filling a key post as the Volkswagen-owned (>> Volkswagen AG) brand grapples with the fallout from the group's emissions scandal.

Peter Mertens, senior vice president for R&D at Volvo Car Corporation who has previously held senior positions at General Motors (>> General Motors Company) and Audi's German rival Mercedes-Benz (>> Daimler AG), will take up his new post as soon as possible, a spokesman for Audi said on Thursday, without being more specific.

Mertens will replace Audi's former R&D chief Stefan Knirsch, who left the premium brand in September.

A source familiar with the matter has told Reuters Knirsch's departure was related to Volkswagen's (VW) investigation into its emissions test cheating scandal, without giving details. Audi and VW have declined to comment. Reuters has not been able to contact Knirsch for comment.

Audi, VW's biggest profit engine, has come under increasing scrutiny for its role in the scandal after VW said earlier this month that Audi cars with automatic transmissions had technology capable of distorting emissions when tested.

With Mertens, Audi is seeking stability after losing four heads of R&D in as many years at a time of intense competition with Mercedes-Benz and BMW (>> Bayerische Motoren Werke AG) in new technologies.

"That (Mertens's appointment) is a good decision," Audi labour boss Peter Mosch said on Twitter. "It's important to further push digitalization and electric mobility."

(Reporting by Andreas Cremer; Editing by Ludwig Burger and Mark Potter)