Toyota Motor North America executive Chris Reynolds said the investments represent yet more examples of the company's long-term commitment to build where it sells, irrespective of trade uncertainty due to tariffs.
Toyota most recently announced an expansion in 2017.
The plant was built as Toyota's first "wholly-owned vehicle manufacturing plant" in the United States.
Toyota announced Thursday that it will add 450 new jobs in Huntsville and exceed its 2017 pledge to invest $10 billion over five years with a new commitment to reach almost $13 billion over the same period.
Toyota President Akio Toyoda will be in Washington Friday to deliver a speech in which he is expected to tout the new investments.
The West Virginia-made hybrid transaxles are to be used in Highlander Hybrids that are built at Toyota's Princeton, Ind., manufacturing plant.
Toyota has 10 U.S. manufacturing facilities and a year ago announced a $1.6 billion joint venture with Mazda to build a plant also in Huntsville that will eventually employ 4,000 workers.
The $288 million investment is going to drive up production 35%, increasing the plant's annual engine capacity from 670,000 to 900,000 by the end of 2021.
Toyota will be one of and more than 200 employers at a job fair planned from 11 a.m.to 3 p.m. on March 22 at the Charleston Coliseum and Convention Center. "Overall, the plant represents an investment of more than $7 billion". The plant has the capacity of 12,000 units.
"Today's exciting announcement shows Toyota's recognition and continued trust in the high-level skills and expertise of our fantastic team here in Kentucky", said Susan Elkington, president of Toyota's Kentucky facility.
Toyota also is spending $62 million on equipment to boost production of Toyota and Lexus cylinder heads at its Bodine Aluminum facility in Troy, Missouri, as part of its cost-saving New Global Architecture production strategy to share common parts and components among different vehicles.
"Toyota has been a wonderful partner for West Virginia. This significant announcement puts the company in position to better serve its customers for years to come, and we look forward to Toyota, Scott County and Kentucky continuing to grow together".