How to pass object in ajax call to function

@model IEnumerable<HitecPoint.BlackBox.Models.SMSReportModal>     
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js"> </script>


<script type="text/javascript">

var MyAppUrlSettings =
{

    DistanceReportURL: '@Url.Action("SmsReport", "SmsReport")',

}
</script>


 <script type="text/javascript" >
   $(document).ready(function () {

    alert('hi');
    //Initialize Page
    initializePage();
    //Distance link click
    $("#SearchS_R").click(function () { getDistanceReport(); });

 });
 function initializePage() {
  $("#SmsReport").html('');
   }


  </script>

 <script type="text/javascript">

function getDistanceReport() {

var obj = {};
obj.BBID = "D527";
obj.Interval = 0;

$.ajax({
    type: "POST",
    url: MyAppUrlSettings.DistanceReportURL,
    data: "{obj:" + JSON.stringify(obj) + "}",
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    success: function (data) {
        if (data.Html) {
            $("#SmsReport").html(data.Html);
        }
        else {
            $("#SmsReport").html("<p style='color: #AFAEAE; font-family: status-bar; font-size: 16px; font-weight: bold; margin: 30%;'> No Data available </p>");
        }
        $("#overlay").fadeOut();
        $("#loading").hide();
    },
    error: function (request, status, error) {
        alert(error);
        $("#overlay").fadeOut();
        $("#loading").hide();
    }
});
}

and my function is below. I have made a class of SMSReportModal in which i have declared all properties of object

public ActionResult SmsReport(SMSReportModal _SMRobj)
    {
        string k = _SMRobj.BBID;
        return Json(true);
    }

I am using razor in Mvc .I want to pass data object to function using ajax, but function returns me null value of object.What mistake I have done.Please help