cannot connect to ppa.launchpad.net

While I was trying to download wine1.7 on Ubuntu, after I add the related repository, and execute sudo apt-get update, I encountered this error.
There is a good link that enlights me.
Use
unset http_proxy
unset https_proxy

Then I try sudo apt-get update again, it still report some link error, but I successfully download wine anyway.
By the way, you can check the settings of proxy of a terminal through env | grep -i proxy