The results are not shown in the iframe

I have this code and I do not know why the results are not shown in the iframe. I have hardly any knowledge and what I am reading on the web does not help anything. Thanks.

<script>
function enviar(){
  dato1 = document.getElementById('dato1').value;
  dato2 = document.getElementById('dato2').value;
  document.getElementById("myform").target = "iframeUpload";
  document.myform.action = 
  "http://www.google.es/maps/search/"+dato1+"+"+dato2;
 document.myform.submit();
}
</script>
<form name="myform" action="" method="get">
<input type="text" value="" id="dato1" />
<input type="text" value="" id="dato2" />
<input type="button" value="enviar" onclick="enviar();" />
 </form>
 <iframe id="iframeUpload" name="iframeUpload"></iframe>