(Adds comments, details, background)
PARIS, Sept 15 (Reuters) - The Renault-Nissan alliance pledged on Friday to double savings from closer integration to 10 billion euros ($11.9 billion) by 2022, thanks in part to increasing cooperation with recently acquired Mitsubishi Motors.
Combined annual sales volumes are expected to rise to 14 million vehicles over the same five-year period from about 10 million today, with revenue advancing by one-third to $240 billion, the alliance said in a statement.
With 5.27 million cars and vans delivered in the first half, ahead of Volkswagen and Toyota, Renault-Nissan now claims the mantle of the world's biggest carmaker - although parent Renault has never consolidated the sales of its 43.4 percent-owned Japanese affiliate into its own.
Alliance Chairman Carlos Ghosn has pledged to step up the pace of integration since Nissan took a controlling stake in Mitsubishi last year. The 18-year-old Renault-Nissan pairing has only recently begun rolling out cars on common architectures.
Under existing plans, the alliance is seeking to increase synergies - from costs cut or avoided and revenue enhancements - to 5.5 billion euros next year from 5 billion recorded in 2016.
A fourth common vehicle platform will be shared across the alliance by 2022, the companies said on Friday, providing the underpinnings for a future generation of electric cars.
Twelve new pure-electric models will be launched by that date as Renault-Nissan seeks to defend the head-start it took with the current generation of battery cars, spearheaded by the Nissan Leaf and Renault Zoe, as more competitors join the fray.
"Without a doubt, what we have seen and acted on and executed eight years ago is becoming mainstream," Ghosn told reporters at a presentation in Paris.
As more models are launched on the new platforms by Renault, Nissan, Mitsubishi and their other brands, shared architectures will account for 70 percent of sales by 2022, with common engines installed in 75 percent.
Friday's announcement was thin on details of how closer convergence would be achieved. Relations between Renault and Nissan engineering teams have sometimes been fraught, hampering savings in areas such as engines and transmissions.
Convergence efforts will continue with no radical change to management structures, Ghosn said, suggesting that he had no immediate plans to stand aside. Ghosn's current contract as Renault chief executive expires next year.
"I am intending to execute on the plan as long as it makes sense," he said.
More information on operational and product strategies and financial goals are expected when Renault, Nissan and Mitsubishi each announce their mid-term plans in coming weeks - starting with the French carmaker on Oct. 6.
($1 = 0.8392 euros) (Reporting by Laurence Frost and Gilles Guillaume; Editing by Sudip Kar-Gupta)