<td><%= button_to '+', {:controller => "votes", :action => "create", :car_id => car.id, :user_id=> session[:user_id]} , :method=>:post %></td>
This will make params[:car_id] and params[:user_id] available in VotesController create action.
<td><%= button_to '+', {:controller => "votes", :action => "create", :car_id => car.id, :user_id=> session[:user_id]} , :method=>:post %></td>
This will make params[:car_id] and params[:user_id] available in VotesController create action.