TOKYO, JAPAN — Isuzu Motors Ltd. expects to increase sales of CNG vehicles in Japan this year by 50 percent over last year — to about 2,000 units, according to the Natural Gas Vehicle Coalition. Isuzu has been promoting the vehicles as a way to lower emissions of NOx and CO2 and will focus on sales of CNG vehicles that use its Elf small truck as their base. In 2006, Isuzu will attempt to top 10,000 units in cumulative sales.