Trip Sheet PDF Load Number

[SandDoller]

Okay, I have it where you can click on the button to download the trip sheet in a PDF file to your computer. It pops-up with a rename the PDF. Right now it comes up with Trip Sheet.pdf I want it to have the Load Number at the end. So it would look like this: Trip Sheet 12342.pdf
I can not figure out how to have it put the load number in. I have tried all sorts of ways. Even asked on the PHPRunner Forum. No Help and they closed the thread on me.. Here is the link:

Here is my button codes:

Client Before:

ajax.addPDF( 'pdf', {}, function() {
 
  return ctrl.dialog( {
     title: 'Save results as PDF',
     fields: [{
        name: 'filename',
        value: 'TripSheet.pdf'
     }]
  });
});
return false;

Server:

$record = $button->getCurrentRecord();
$result["trip_number"]=$record["trip_number"];

$filename = str_replace( array( '/', '\\'), '', $params["filename"]);

$dot = strrpos( $filename, "." );
if( strtolower(substr( $filename, $dot )) !== '.pdf' ) {
  $filename .= '.pdf';
}
file_put_contents( $filename, $params["pdf"] );?

Client After:

window.open( params['filename'] );

This button is on the Trip Sheet page and my data value I need is trip_number