The only way to prevent your oak tree from fruiting is to inhibit the flowering and pollination of your tree (other than cutting down the tree, which may or may not be a valid option).
There are growth regulators on the market (e.g., Florel) that "may" be used to inhibit flowering and pollination. Unfortunately, the product application window is extremely small.
My personal suggestion would be to install a small tarp or canopy to re-direct the acorns dropping on your vehicle(s). It's not an ideal fix to your problem, but it will likely be cheaper than reapplying growth regulator every year :-)
Best of luck!