Codeigniter - Extending Core Class

hello.php

<?php 

class Hello extends MY_Controller {

	public function index() {

		echo $this->model->foo();
		
	}
}

My_Controller.php

<?php

class MY_Controller extends CI_Controller {

	public function __construct() {

		parent::__construct();

		$controller = get_class($this);
		$model = $controller . '_model';

		$this->load->model($model, 'model');
	}
}