That SELECT statement is being constructed from within 'part_equipo_xref', so it can only include automatic JOINs for relationships where 'part_equipo_xref' is the child.
If you wish to modify the SELECT statement which is constructed automatically then you need to follow the instructions at http://www.tonymarston.net/php-mysql/infrastructure-faq.html #faq84, as in the following example:
function _cm_pre_getData ($where, $where_array, $fieldarray=null)
{
// construct default SELECT and FROM clauses using parent relations
$this->sql_select = null;
$this->sql_from = null;
$this->sql_groupby = null;
$this->sql_having = null;
$this->sql_from = $this->_sqlForeignJoin($this->sql_select, $this->sql_from, $this->parent_relations);
// add code to obtain facility_name
$this->sql_select .= ', categoria.fecini, categoria.fecfin';
$this->sql_from .= ' LEFT JOIN categoria ON (categoria.categoria_id=equipo.categoria_id)';
return $where;
} // _cm_pre_getData