ROSEVILLE, Minn. — Horton Holding Inc. will launch in September new variable-speed fan drives and fan blades designed to improve commercial vehicle cooling system performance and help engine makers meet the increasingly stringent requirements in Phase 2 of the federal greenhouse-gas regulations.

Many in the industry say variable-speed drives, which run only as fast as necessary, are increasingly popular. Variable drives can save on horsepower and therefore save on fuel. However, the more traditional on-off drive also is a popular choice because it’s simplest and cheapest.