You should be able to not enclose the fields in anything and just use the pipes to separate the columns. If you have to enclose it in something, use single quotes, then strip them out on import with:
$column_data = trim( $column_data, '\'' );
When you create the file, also make sure your actual data doesn't include any pipes. You can escape them (replace any pipe with a backslash then a pipe), or replace them with some kind of placeholder, like:
$column_data = str_replace( '|', '[PIPE]', $column_data); //do the opposite when displaying