Catchable fatal error: Object of class SQLite3Result could not be converted to string

This is my Code:

        $bvl = $vbclD->BVL_ID;
        $vbl = $vbclD->VBCL_ID;
        $vpal = $vbclD->VPAL_ID;
        $topleft = $vbclD->Coordinate_topleft;

        $query = "INSERT INTO VBCLDetails (BVL_ID,VPAL_ID,VBCL_ID,Coordinate_topleft) VALUES (". $bvl .",". $vpal . "," . $vbl . ",'" .$topleft . "')";
        $result = $this->query($query);

the error is in line containing insert query. Here vbclD is an object carrying values to enter in database. anybody please help me solve this problem. :)