在高图中改变x轴标签与轴的距离

I want to increase the distance of the x axis title from x axis in highchart.

following is my x axis code.But using this code title is too close to the x axis.

I try with x and y values but no difference in output.

    xAxis:
            {
                categories: [<?php echo $ffdat;?>],
                title:
                {
                    text: 'Overall Average Mean Time Between Failures: <?php echo round($avg, 2);?> Hrs.'
                },
            },

use margin property to provide spacing between axis and title

title:{
   margin: 60
}

here is a working example for it http://jsfiddle.net/5kZbG/

Hope this will solve your issue.