rotating object joystick rotation direction current object independently

All respondents found here related to my question no get what I want. I need to rotate an object in the direction of joystick initially angles of the object is zero and if I move the joystick horizontally or vertically right turns but when you change the rotation no longer follows the direction of the joystick, I need regardless of the angle rotation that already has the object continue turning horizontally or vertically, is in the rotation that is currently subject.

The code does not work properly:

 function Update() {
      transform.Rotate(Vector3(-Input.GetAxis("Vertical")*0.5,0,Input.GetAxis("Horizontal2")*0.5));        
 }

Thank you very much in advance.