Route::set('post', 'post/<year>/<month>/<day>/<title>', array('year'=>'\d{4}', 'month'=>'\d{2}', 'day'=>'\d{2}'))
->defaults(array(
'controller' => 'post',
'action' => 'index',
));
Controller function
public function action_index($year, $month, $day, $title){
//Your code here
}
or
Request::instance()->param('year') ...
Enjoy