yii session 设置过期时间不起作用 [ 1.1 版本 ]

先描述一下我遇到的问题，我的session’__userInfo‘ 总是无缘无故消失，
造成Yii::app()->user->getIsGuest() 还是登录状态，
但是Yii::app()->user->__get('u_id')就报错了。
然后我设置了session 过期时间是3秒,但是它过很久也不过期。
我研究了好久，我错过了什么配置吗？

class WebUser extends CWebUser 
{ 

    public function __get($name) 

    { 
        if ($this->hasState('__userInfo')) { 
            $user=$this->getState('__userInfo',array()); 
            if (isset($user[$name])) { 
                return $user[$name]; 
            } else {
                return null;
            }
        } 
        return parent::__get($name); 
    } 

    public function login($identity, $duration) { 
        $this->setState('__userInfo', $identity->getUser()); 
        parent::login($identity, $duration); 
    } 
} 
class WebUserIdentity extends CUserIdentity
{

    private $_id;
    private $_isssd;
    public $realname;
    public $is_login;
    public $user;

    public function authenticate()
    {
        $record = User::model()->findByAttributes(array('email'=>$this->username));
        if($record===null)
        {
            $this->errorMessage = '用户名不存在';
            $this->errorCode=true;
        }
        else if($record->password!==md5($this->password))
        {
            $this->errorMessage = '密码不正确';
            $this->errorCode=true;
        }
        else
        {
            $this->_id=$record->u_id;
            $this->_isssd=$record->u_id;
            $this->errorCode = false;

            $this->setUser($record);
        }
        return !$this->errorCode;
    }

    public function getId()
    {
        return $this->_id;
    }

    public function getUser()
    {
        return $this->user;
    }

    public function setUser($record)
    {
        $this->user=$record;
    }

}

user model

public function check_user($attribute,$params)
{
    $this->_identity = new WebUserIdentity($this->email,$this->password);
    $res = $this->_identity->authenticate();	
    if($res == true){
    	$duration=Yii::app()->params['sessionTimeoutSeconds'];//(=3)
    	Yii::app()->user->login($this->_identity,$duration); 
        return true;
    }else{
        return false;
    }
}

main.php

'session'=>array(
    'class'=>'application.components.WHttpSession',
    'timeout'=>3,
),