Ford Motor Co. plans to sell less than 20% of its Hertz Corp. car rental unit in an initial public offering. The auto maker told the Securities and Exchange Commission that the offering, which had been long expected, will involve newly issued shares of Hertz common stock. Ford first invested in the Park Ridge, N.J.-based car rental giant in 1987 and acquired full control in 1994. Pricing of the Hertz shares is several weeks away, a Ford spokesman said. Ford wants to keep more than 80% of Hertz so it can continue to consolidate Hertz's earnings on its books for tax purposes, the spokesman said, adding that it's premature to say whether more of the Hertz stake may be sold later.