Problem of accents in the name of a file with codeigniter

I am trying to upload files to my server with codeigniter 3, the program uploads the files without accent like tilde or Latin characters like Ñ, but when uploading a file with an accent like tilde or Ñ the name and shape me problem when downloading, because when I save it, it is named after me Chapter_11 the name would be Chapter_11, and when trying to download it, it does not find the file and it sends it to me with read error, it tells me if a pdf file can not be opened, in case of a document office can not read or open the file because it is damaged.

The data sent by ajax and e checked that sent correctly with accents and everything.

Here is my code to upload a file to the server:

public function document()
{
    $config['allowed_types']    = 'docx|xlsx|pdf';
    $config['upload_path']      = './assets/archivos/doc/';
    $config['remove_spaces']    = TRUE;
    $config['max_size']         = '20048';
    $this->load->library('upload', $config);
    if(!$this->upload->do_upload('file')){
         $error = $this->upload->display_errors();
         $result = array('error' => true, 'mens' => $error, 'estado' => 3);
         echo json_encode($result);
    }else{
         $data = array(
                 'nom_doc'  => $this->upload->data('file_name'), 
                 'doc_size' => $this->upload->data('file_size'),
                 'type_doc' => $this->upload->data('file_type'),
                 'ruta_doc' => $this->upload->data('full_path'),
                 'id_conf_sist' => 1
                 );
         $res = $this->Config_model->insertDocument($data);
        if($res){
              $result = array('error' => false, 'mens' => 'El archivo '.$this->upload->data('raw_name').', a sido guardado correctamente.', 'estado' => 1);
             echo json_encode($result);
         }
      }
 }

Someone could help me to solve this problem.