robot_localization:fusion of IMU and visual inertial odometry(VIO)

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Hi, I try to use the acceleration x,y,z from IMU and position x,y,z from VIO to estimate linear velocity x,y,z(on the drone).

At first, when the drone is put on the ground, the result of the estimated linear velocity is normal(linear velocity x, y and z are all approximately zero.) But when I move the drone, the linear velocity starts to jump to large value. And the estimated linear velocity is no longer correct.

However, I try to only use x and z dimensions, and it works well. I also try to only use y dimension, it works well, too. Is there anything wrong with my data or parameters? The following is my sensor data and parameters:

IMU:

header: 
  seq: 1682
  stamp: 
    secs: 1523248805
    nsecs: 647093568
  frame_id: "base_link"
orientation: 
  x: -0.0122626064765
  y: 0.00367087394292
  z: 0.916815569843
  w: -0.399105809831
orientation_covariance: [1.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 1.0]
angular_velocity: 
  x: 0.000395756680518
  y: -0.000165232922882
  z: -0.00103721336927
angular_velocity_covariance: [1.2184696791468346e-07, 0.0, 0.0, 0.0, 1.2184696791468346e-07, 0.0, 0.0, 0.0, 1.2184696791468346e-07]
linear_acceleration: 
  x: -0.0284779034555
  y: 0.0534957796335
  z: 9.84046649933
linear_acceleration_covariance: [8.999999999999999e-08, 0.0, 0.0, 0.0, 8.999999999999999e-08, 0.0, 0.0, 0.0, 8.999999999999999e-08]

VIO:

header: 
  seq: 2277
  stamp: 
    secs: 1523248919
    nsecs:  87182999
  frame_id: "odom"
pose: 
  pose: 
    position: 
      x: -0.0103095776711
      y: -0.0177321412212
      z: -0.00803798318176
    orientation: 
      x: 0.054222564786
      y: -0.0293635843474
      z: -0.0371067739578
      w: 0.997407028604
  covariance: [2.807622030235894e-05, -2.058458623309457e-05, -3.3721156419156076e-06, 0.997407028604045, -0.010309577671119459, -0.017732141221179724, -0.00803798318175729, -0.0, -0.05422256478599025, 6.95230206988004e-310, 5e-324, 1.91256606e-316, 6.95236747896094e-310, 6.95235731875666e-310, 6.95235117641476e-310, 6.95241666970836e-310, 6.9523573187701e-310, -3.02085629259538e+94, 6.95235117641476e-310, 6.95230206988004e-310, 6.95230206988004e-310, 6.95230206988004e-310, 5e-324, 1.91256606e-316, 6.95236747896094e-310, 6.95236735079744e-310, 2e-323, 6.9523573187598e-310, 6.95235731876377e-310, 6.9523573187527e-310, 7.65732518758802e-207, 6.9523573187602e-310, 6.95235731875666e-310, 6.9523573187551e-310, 6.95230206987925e-310, 6.95230206988004e-310]

Params:Bellow is part of the parameters. If you want to check all the parameters, please see the link. parameters

odom_frame: odom           
base_link_frame: base_link  
world_frame: odom           

pose0: /svo/pose_imu2
pose0_config: [true,  true, true,
               false, false, false,
               false, false, false,
               false, false, false,
               false, false, false]
pose0_differential: false
pose0_relative: false
pose0_queue_size: 1
pose0_rejection_threshold: 2  # Note the difference in parameter name
pose0_nodelay: false

imu0: /drone2/mavros/imu/data
imu0_config: [false, false, false,
              false, false, false,
              false, false, false,
              false, false, false,
              true, true, true]
imu0_nodelay: false
imu0_differential: false
imu0_relative: true
imu0_queue_size: 1
imu0_pose_rejection_threshold: 5                 # Note the difference in parameter names
imu0_twist_rejection_threshold: 5               #
imu0_linear_acceleration_rejection_threshold: 8  #