BERLIN/FRANKFURT (Reuters) - An investigation commissioned by Volkswagen <VOWG_p.DE> into its emissions test cheating scandal has found no evidence against the head of its Audi luxury car division, three people familiar with the matter said.

Audi Chief Executive Rupert Stadler was questioned earlier this week by U.S. law firm Jones Day, which is conducting the investigation, about when he found out about the use of test-cheating software, the people said.

The findings are due to be discussed by Volkswagen's (VW) supervisory board on Friday, they added.

Audi and VW declined to comment, while Jones Day's German office did not respond to a request seeking comment.

Audi, the main contributor to VW group profit, has admitted its 3.0 liter V6 diesel engine was fitted with emissions-control software, deemed illegal in the United States where VW's diesel emissions scandal broke a year ago.

The questioning of Stadler, who has led Audi since 2007, coincided with media reports that the brand was more deeply entangled in the VW scandal than previously thought. Audi has declined to comment on those reports.

"Nothing burdensome against Stadler was found," a source close to VW's supervisory board said on Friday.

Two sources close to Audi also said the questioning by Jones Day had yielded no evidence against Stadler, who joined VW group's nine-member executive board in 2010.

Other investigations are ongoing.

Three U.S. states alleged in their civil lawsuits against VW published in July that senior executives had covered up evidence about rigged U.S. emissions tests for years.

Ingolstadt-based Audi last November denied accusations that its 3.0 liter engines were implicated, only to admit weeks later to using illicit emissions-control devices.

Unlike parent VW which has reached a settlement with U.S. authorities on 2.0-litre engines, Audi has yet to find a technical solution for about 85,000 3.0-litre engines used in Audi, Porsche and VW brand models.

(Reporting by Ilona Wissenbach, Andreas Cremer, Irene Preisinger and Jan Schwartz; Editing by Tina Bellon and Mark Potter)