Why does seesion expire too soon?

[eluser]behnampmdg3[/eluser]
Hello

Why does the session expire in a few minutes? Sometimes 5 minutes, sometimes 1, sometimes 10? This is how I create it:

Code:

$user_data = array('email'=>$results['email'], 'id'=>$results['id'], 'login'=>true);
$this->session->set_userdata($user_data);

Thanks