Insert portfolio post by php code

Hi, I have a script to insert automatically 500 portfolio posts with
– the content generated automatically
– the title, the url and the
– attached image also generated automatically
– the associated category exists already

If I insert a normal post, just by saying
$my_post=array(
‘post_title’ => $title,
‘post_date’ => $time,
‘post_date_gmt’ => get_gmt_from_date( $time ),
‘post_content’ => $content,
‘post_type’ => portfolio
);
$pid= wp_insert_post( $my_post );
wp_set_object_terms( $pid, $categorien[$cat], ‘portfolio_entries’, true );
set_post_thumbnail( $pid, $thumbnails[$j] );

the post is not really a portfolio post. Which functions should I use instead?
Thanks