By 2020, Beijing says automakers must meet tough new green standards to cut epic pollution in China’s cities. As domestic firms bet heavily on electric cars to meet that goal, foreign peers are set to stay in a different, petrol-driven gear. In the latest sign of caution from global automakers in China, Germany’s Audi last week unveiled a new factory for high-efficiency transmissions in Tianjin, to be used in petrol-powered cars. While Chinese firms go…