As you may know, by using the following url, you can \'ping\' google to update its record of your sitemap:
https://www.google.com/ping?sitemap=URLOFSITEMAP.x
As of 2015, Google no longer suggests a rate limit in their documentation.
It is in Google's best interest to know when fresh articles are created so it is worth pinging them with your sitemap, or at least some kind of "Fresh Articles" sitemap when new articles are published.
Googlebot will request your sitemap every time your ping it. It sends requests headers to check the newness of the resource. So if you plan on submitting a sitemap frequently, make sure your server will handle the request correctly. Otherwise, you might return a 304 (Not Modified) and Googlebot won't actually get the file.