[{"my_object":{"1":{"seq":"1","time":"xyz",},"2":{"seq":"2","time":"abc","sub_aray":{"0":{"value":10},"1":{"value":10},"2":{"value":-10}}}}}]

db.collection.aggregate([{$project:{"array":{"$objectToArray":"$my_object"}}},{"$unwind":"$array"},{$project:{"k":{"$objectToArray":"$array.v.sub_aray"},"seq":"$array.v.seq"}},{"$project":{"sub_array":{$sum:"$k.v.value"},"_id":0,"seq":1}}])