How can I get an arrangement made in jquery?

I will explain what I want to do, I from a file js create an array in which I will generate associative indexes (if that is how you can call them). After creating the array I try to send it through ajax to a php file, but when trying to receive the array it comes empty, I tried with JSON.stringify () before sending it and receiving it with a json_decode () but it did not work for me.

This is my code in js (diculpen if my code is something murky I'm still a novice in this, thank you)

var array_datos = [];

function llenarArreglo()
{
    if(array_datos[unidad] === undefined) array_datos[unidad] = [];
    if(array_datos[unidad]['Apartado'] === undefined) array_datos[unidad]['Apartado'] = [];
    if(array_datos[unidad]['Apartado']['Fecha'] === undefined) array_datos[unidad]['Apartado']['Fecha'] = [];
    if(array_datos[unidad]['Apartado']['Valor'] === undefined) array_datos[unidad]['Apartado']['Valor'] = [];

    if(array_datos[unidad]['Apartado']['Fecha'][cont] === undefined)
    {
       array_datos[unidad]['Apartado']['Fecha'][cont] = fecha;
    }
    if(array_datos[unidad]['Apartado']['Valor'][cont] === undefined)
    {
      array_datos[unidad]['Apartado']['Valor'][cont] = valor;
    }
};

$('#boton_guardar').on('click', function(){
    var obj = $.ajax({
        method: 'POST',
        url: 'procesar.php',
        data: {
            evento: 'guardar',
            datos: array_datos
        },
        beforeSend: function(){

        }
    }).done(function(data){
        console.log(data);
    });
});

and in PHP I get it this way

$evento = filter_input('INPUT_POST', 'evento');
switch($evento)
{
    case 'guardar':
        $datos = filter_input('INPUT_POST', 'datos', FILTER_DEFAULT, FILTER_REQUIRE_ARRAY);
        print_r($datos);
    break;
}