TOKYO, Feb. 20 Japanese truck maker Nissan Diesel Motor Co. said Tuesday it accepted a billion-dollar buyout from Sweden's Volvo Group.Volvo will make Nissan Diesel a subsidiary, the companies said.Volvo has owned 19 percent of Nissan Diesel after buying Nissan Motor Co.'s 13 percent in 2006. Nissan Motor divested the truck maker to focus on lighter vehicles.Volvo has meanwhile concentrated on trucks, after selling its auto division to the Ford Motor Co. in 1999.Tuesday's deal will let the combined company increase its investment in research and development to meet tighter vehicle-emissions regulations that go into effect in the United States, Japan and much of Europe in the next three years, Volvo said.Nissan Diesel said the offer represented a 32 percent premium on the company's average price on the Tokyo Stock Exchange over the past three months.The Swedish company said it would pay for the purchase with cash and by taking on debt.Copyright 2007 by UPI