I am overriding Usa\Model\Shipping\Carrier\Ups.php but its not working. i want update this function collectRates() code below

what's the problem

app/etc/modules/TechnikExpert_Usa.xml
<?xml version="1.0"?>
<config>
  <modules>
    <TechnikExpert_Usa>
      <active>true</active>
      <codePool>local</codePool>
    </TechnikExpert_Usa>
  </modules>
</config>


app\code\local\TechnikExpert\Usa\etc\config.xml
<?xml version="1.0"?>
<config>
  <modules>
    <TechnikExpert_Usa>
      <version>0.1</version>
    </TechnikExpert_Usa>
  </modules>
  <global>
    <models>
      <usa>
        <rewrite>
          <shipping_carrier_ups>TechnikExpert_Usa_Model_Shipping_Carrier_Ups</shipping_carrier_ups>     
      </usa>
    </models>
  </global>
</config>

app\code\local\TechnikExpert\Usa\Model\Shipping\Carrier\Ups.php

<?php
 class TechnikExpert_Usa_Model_Shipping_Carrier_Ups extends Mage_Usa_Model_Shipping_Carrier_Ups
{
   
    const CODE = 'ups';

    /**
     * Delivery Confirmation level based on origin/destination
     *
     * @var int
     */
    const DELIVERY_CONFIRMATION_SHIPMENT = 1;
    const DELIVERY_CONFIRMATION_PACKAGE = 2;

    /**
     * Code of the carrier
     *
     * @var string
     */
    protected $_code = self::CODE;

    /**
     * Rate request data
     *
     * @var Mage_Shipping_Model_Rate_Request|null
     */
    protected $_request = null;

    /**
     * Raw rate request data
     *
     * @var Varien_Object|null
     */
    protected $_rawRequest = null;

    /**
     * Rate result data
     *
     * @var Mage_Shipping_Model_Rate_Result|null
     */
    protected $_result = null;

    /**
     * Base currency rate
     *
     * @var double
     */
    protected $_baseCurrencyRate;

    /**
     * Xml access request
     *
     * @var string
     */
    protected $_xmlAccessRequest = null;

    /**
     * Default cgi gateway url
     *
     * @var string
     */
    protected $_defaultCgiGatewayUrl = 'http://www.ups.com:80/using/services/rave/qcostcgi.cgi';

    /**
     * Default urls for XML
     *
     * @var array
     */
    protected $_defaultUrls = array(
        'Rate'        => 'https://onlinetools.ups.com/ups.app/xml/Rate',
        'Track'       => 'https://onlinetools.ups.com/ups.app/xml/Track',
        'ShipConfirm' => 'https://onlinetools.ups.com/ups.app/xml/ShipConfirm',
        'ShipAccept'  => 'https://onlinetools.ups.com/ups.app/xml/ShipAccept',
    );

    /**
     * Container types that could be customized for UPS carrier
     *
     * @var array
     */
    protected $_customizableContainerTypes = array('CP', 'CSP');

    /**
     * Collect and get rates
     *
     * @param Mage_Shipping_Model_Rate_Request $request
     * @return Mage_Shipping_Model_Rate_Result|bool|null
     */

    public function collectRates(Mage_Shipping_Model_Rate_Request $request)
    {
         die('function called');  
    }
}