使用curl更新firebase数据，而不删除已存储的数据

so I have been working on this code and I cant put my finger on it I am using php to send data to firebase. this one send the data how I want it but any data that I already have in it erases it instead of updating it how I want.

  $url = 'https://granted-7cdeb.firebaseio.com/maps.json';
   $arr = array($mapId =>array($bike =>array("coords"=>array("latitude"=>$lat, "longitude"=>$lng), "orientation"=>$ori, 
  "timestamp"=>$time)));  
   $data_string = json_encode($arr);
   $ch = curl_init($url);
   curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "PATCH");
   curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);
   curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
   curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
   curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
   curl_setopt($ch, CURLOPT_HTTPHEADER, array(
   'Content-Type: application/json',
   'Content-Length: ' . strlen($data_string))
   );
   echo $result = curl_exec($ch);

and this is the result I receive when I execute this code

{"2":{"suzuki":{"coords":{"latitude":32.6990593,"longitude":-117.0279802},"orientation":259.61241243675,"timestamp":1536138065}}}

when I try it this way

 $url = 'https://granted-7cdeb.firebaseio.com/maps.json';
   $arr = array($mapId =>array($bike =>array("coords"=>array("latitude"=>$lat, "longitude"=>$lng), "orientation"=>$ori, 
  "timestamp"=>$time)));  
      $data_string = json_encode($arr);
   $ch = curl_init($url);
   curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);
   curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
   curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
   curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
   curl_setopt($ch, CURLOPT_HTTPHEADER, array(
   'Content-Type: application/json',
   'Content-Length: ' . strlen($data_string))
   );
   echo $result = curl_exec($ch);

it uploads multiple arrays but instead of updating its lat and lng it creates a name and upload multiple times

{"name":"-LLcxfR1R7w2j5FcWhdA"}

please help me I am trying to accomplish sending a array of this nature

{"2":{"suzuki":{"coords":{"latitude":32.6990593,"longitude":-117.0279802},"orientation":259.61241243675,"timestamp":1536138065}}}

I have a website that tracks a users location and send it to my firebase table MAPS then I plot the user location so they can view each others location.