BYD made a statement on Monday saying its plug-in hybrid electric vehicles (PHEVs) comply with emission rules thanks to an optimized dual-motor power supply that controls the auto emission of fuel vapor during operation and while parked. 

The Chinese EV giant claimed its PHEVs could drive in parallel or series mode, enabling the engine and electric motor to provide power independently and limiting the evaporation of gasoline while the vehicle runs.

This means the vehicles achieve compliance despite using non-pressurised fuel tanks in some cases worldwide, the Shenzhen and Hong Kong-listed company said in a statement to investors, voicing its willingness to share relevant patents with rivals “for free.” 

The explanation comes after rival Great Wall Motor said on May 25 that it had filed a report with Chinese regulators alleging emission control rules violations by BYD because of the use of cheaper fuel tanks. 

[BYD statement, in Chinese]